Author Topic: Space Solar Power with BFR  (Read 70550 times)

Offline alexterrell

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Space Solar Power with BFR
« on: 05/01/2018 12:07 pm »
(This might be a topic for elsewhere, but SpaceX might be a game changer for this, to the annoyance of Musk)

Certainly, space solar power has long been dismissed, primarily due to
1. High launch costs (the original idea killer - coupled with falling oil prices)
2. A lack of space capability meaning we can't make the power sats from asteroids or lunar material.

And here is what Musk said, a few year back:
Quote
You see, that's the point I'm making. Take any given solar cell: is it better to have on Earth or in orbit? What do you get from being in orbit? You get twice as much sun, best case. But you've got do do a conversion. You've got incoming photons that go to electrons, but you have to do two conversions you don't have to do on Earth. You've got to convert it to photons and then convert those photons back into electrons.

And that double conversion is going to get you back to where you started basically! So why are you sending them to bloody space?

And by the way, electron to photon converters are not free, nor is sending stuff to space. So then it obviously super-doesn't work.

Case closed! You'd think case closed! But no, I guarantee it's gonna come up another ten times! I mean, for the love of god!

Case closed? Now, I know questioning Musk is unwise these days, but could BFR prove him wrong?

For starters, Musk badly gets his facts wrong above (reality distortion fields can be dangerous). A solar panel in space will deliver ten times as much energy per square metre as most fixed panels on Earth (maybe a steerable array in the Atacama desert could get one third of an orbital array's output - but solar PV is almost always fixed - in orientation and latitude).

And ... two big changes:
- Solar panels can be made lighter in space. How light? Thin film technology is talking about better than 1000W/kg (http://www.spacefuture.com/archive/early_comme
rcial_demonstration_of_space_solar_power_using_ultra_lightweight_arrays.shtml).
- BFR is promising an order of magnitude reductions in launch cost (and orders of magnitude increase in supply).

Let's consider a 6 GW array, delivering 4GW to Earth's grid.
Mass of solar system 6,000 tons
Total mass 10,000 tons in LEO, including fuel for electric thrusters to move sections to GEO. (Assuming the microwave transmitter is light enough)

BFR is being discussed as having a launch cost, once fully operational, of below $100/kg. That means the 10,000 ton solar station would have a launch cost of only $1 billion.

4GW on Earth - average power - could be delivered by about 30GW of solar arrays (Low latitude USA - would need 40GW in Europe). Solar cell prices are stabilising but 30GW of capacity might be installable for $30 billion. (The Saudis are talking about 200GW for$200 billion - https://www.bloomberg.com/news/articles/2018-03-28/saudi-arabia-softbank-ink-deal-on-200-billion-solar-project).

And that of course is for highly intermittent power - especially in higher latitudes where solar is not much use in winter, when electricity demand is higher.

The 6GW of solar cells in orbit will also cost. Traditionally, you'd say that they would cost a lot more than 6GW of Earth cells, but since a large part of Earth cell costs is now supporting aluminium and protective, that may not always be the case.

Let's say Space Power Sat at $1 billion launch plus $6 billion structures, plus $3 billion ground array, total $10 billion, compared to $30 billion, plus a huge amount of storage, for the Earth based solution.

Space Solar Power being baseload - it makes sense to compare it to nuclear. Hinkley C is costing $8,000/KW, or $32 billion for 4GW. OK - that one's expensive, but even with a better PWR 4GW will cost $20 billion. (Barakah in UAE is about $25 billion for 5.38GW - but would cost more in the USA or EU).

These space figures are of course optimistic. But there is a lot of leeway to rise, and still it turns out cheaper.  I'm very sceptical of the claims for BFR, but even it costs $1000/kg - that would add $9 billion: Still affordable. 

So I think the original reason why space solar power turned out too expensive will be gone within a decade. Of course, there will be plenty of other reasons why Space Solar Power might not work, but the economics could start to add up. Thanks to SpaceX.
« Last Edit: 05/01/2018 07:40 pm by Chris Bergin »

Offline JBF

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Re: Space Solar Power with BFR
« Reply #1 on: 05/01/2018 12:27 pm »
What are your losses both in transmission and conversion?
"In principle, rocket engines are simple, but that’s the last place rocket engines are ever simple." Jeff Bezos

Offline alexterrell

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Re: Space Solar Power with BFR
« Reply #2 on: 05/01/2018 01:26 pm »
My losses? None :)

I think the original NASA / Glaser studies assumed a fairly high DC-DC efficiency of about 80%.

This link
https://www.allaboutcircuits.com/news/wireless-power-transmission-of-solar-energy-from-space/ suggests:
Quote
The solar arrays attached to a typical satellite generating 1.6GW in space and an average of 1GW on Earth would measure about 5 to 6 square kilometers and use a transmitting antenna array with a diameter of about 1 km.

https://spectrum.ieee.org/green-tech/solar/how-japan-plans-to-build-an-orbital-solar-farm
This talks about >70% for DC to microwaves, and >80% for microwaves to DC.
(Also interesting stuff about Japanese R&D on this area. Their missing ingredient might be cheap launch costs).

Anything above 50% (DC to DC) is not a major issue if BFR is as cheap as Musk hopes.

Offline Elmar Moelzer

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Re: Space Solar Power with BFR
« Reply #3 on: 05/01/2018 01:42 pm »
I don't understand how you get to 10 times more in orbit than on the ground. The solar intensity at 1 AU is 1.36 kW. On the ground it is about 1 kW, depending on where you are, the weather, etc. A space based solar power station would have to be in a geostationary orbit. So the BFS would have to be refueled for getting the panels into a high enough orbit, since its payload to GEO is relatively small.

Offline NuclearFan

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Re: Space Solar Power with BFR
« Reply #4 on: 05/01/2018 01:57 pm »
You should take into account the development costs of building the transmission system, which needs to be about 10,000x longer range than current technology, building such an enormous satellite that can survive debris impact/puncture and point at the sun while keeping the transmitter pointed at Earth, and the massive expanding solar sheets.  Even satellites today are more expensive than their launch costs, several ton communication sats are >$100 million.  Sure, a solar panel farm will be cheaper/kg by far, but also 1000s of times heavier.

Offline alexterrell

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Re: Space Solar Power with BFR
« Reply #5 on: 05/01/2018 02:00 pm »
I don't understand how you get to 10 times more in orbit than on the ground. The solar intensity at 1 AU is 1.36 kW. On the ground it is about 1 kW, depending on where you are, the weather, etc.

Because capacity factors for fixed solar on the ground are between about 0.1 (Germany, England) and 0.2 (Atacama desert).

In GEO, assuming steering, it will be >0.99.

So 5 to 10 times the CF, and 1.36 times the intensity, gives 7 to 14 times the output.

Quote
A space based solar power station would have to be in a geostationary orbit. So the BFS would have to be refueled for getting the panels into a high enough orbit, since its payload to GEO is relatively small.
I would assume modules would be assembled in LEO - perhaps 100MW at a time. Then, with massive amounts of electricity available, electric propulsion would be optimum, with the highest possible Isp.

In this respect, the architecture is very much as outlined by Peter Glaser in 1968, but with BFRs instead of Shuttles.

Offline philw1776

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Re: Space Solar Power with BFR
« Reply #6 on: 05/01/2018 02:02 pm »
I don't understand how you get to 10 times more in orbit than on the ground. The solar intensity at 1 AU is 1.36 kW. On the ground it is about 1 kW, depending on where you are, the weather, etc. A space based solar power station would have to be in a geostationary orbit. So the BFS would have to be refueled for getting the panels into a high enough orbit, since its payload to GEO is relatively small.

This cost, and neglecting conversion losses are precisely why Musk eschews space solar.
This thread is moot given Musk's stated objections un-addressed by proponents.  Why in a SpaceX thread?
If space solar ever happens, which I doubt, it will be done via a lunar construction base.  Bezos?
It's an act of faith on my part bolstered by advances in powerful magnets containment et. al. but fusion power in the 2030s will finally kill the Rube Goldberg scheme of space solar and its ground rectennas.
« Last Edit: 05/01/2018 02:03 pm by philw1776 »
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Offline speedevil

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Re: Space Solar Power with BFR
« Reply #7 on: 05/01/2018 02:11 pm »
I don't understand how you get to 10 times more in orbit than on the ground. The solar intensity at 1 AU is 1.36 kW. On the ground it is about 1 kW, depending on where you are, the weather, etc. A space based solar power station would have to be in a geostationary orbit. So the BFS would have to be refueled for getting the panels into a high enough orbit, since its payload to GEO is relatively small.
I assume it's the weather, but 10* is too pessimistic.

Neglecting spectral effects (some of the 1.36kW is not going to be useful) and assuming that's claiming 136W/m^2 average insolation to solar panels. Or put another way, 1191kWh/year.
Multiplying by a possibly optimistic 20% loss, that comes out to 900kWh/m^2/year.


900kWh/m^2 is beaten even in most of Scotland.

In my part of Scotland, fixed panels get 1240kWh/m^2/year, 2 axis trackers 1600.
In more moderate climates (middle of France) it's around 1520kWh/m^2/1990.
And in Arizona/north-Africa like climates, 2110/2960.

In the best climates, with trackers, it's much closer to 3* than 10*.

10* is only gotten in places where people basically don't live.

Offline LM13

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Re: Space Solar Power with BFR
« Reply #8 on: 05/01/2018 02:31 pm »
My losses? None :)

I think the original NASA / Glaser studies assumed a fairly high DC-DC efficiency of about 80%.

This link
https://www.allaboutcircuits.com/news/wireless-power-transmission-of-solar-energy-from-space/ suggests:
Quote
The solar arrays attached to a typical satellite generating 1.6GW in space and an average of 1GW on Earth would measure about 5 to 6 square kilometers and use a transmitting antenna array with a diameter of about 1 km.

https://spectrum.ieee.org/green-tech/solar/how-japan-plans-to-build-an-orbital-solar-farm
This talks about >70% for DC to microwaves, and >80% for microwaves to DC.
(Also interesting stuff about Japanese R&D on this area. Their missing ingredient might be cheap launch costs).

Anything above 50% (DC to DC) is not a major issue if BFR is as cheap as Musk hopes.

I'm not an electrical engineer and so am out of my depth when discussing antenna dimensions, but is there any way to use a smaller antenna?  How does antenna diameter relate to electrical power, and to distance, and the size of the receiving rectenna? 

Offline Elmar Moelzer

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Re: Space Solar Power with BFR
« Reply #9 on: 05/01/2018 02:41 pm »
I assume it's the weather, but 10* is too pessimistic.

Neglecting spectral effects (some of the 1.36kW is not going to be useful) and assuming that's claiming 136W/m^2 average insolation to solar panels. Or put another way, 1191kWh/year.
Multiplying by a possibly optimistic 20% loss, that comes out to 900kWh/m^2/year.


900kWh/m^2 is beaten even in most of Scotland.

In my part of Scotland, fixed panels get 1240kWh/m^2/year, 2 axis trackers 1600.
In more moderate climates (middle of France) it's around 1520kWh/m^2/1990.
And in Arizona/north-Africa like climates, 2110/2960.

In the best climates, with trackers, it's much closer to 3* than 10*.

10* is only gotten in places where people basically don't live.
That is what I thought as well. I have seen similar math exercises and there never was a factor of 10 improvement.

Offline alexterrell

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Re: Space Solar Power with BFR
« Reply #10 on: 05/01/2018 02:48 pm »
This cost, and neglecting conversion losses are precisely why Musk eschews space solar.
This thread is moot given Musk's stated objections un-addressed by proponents.  Why in a SpaceX thread?
If space solar ever happens, which I doubt, it will be done via a lunar construction base.  Bezos?
It's an act of faith on my part bolstered by advances in powerful magnets containment et. al. but fusion power in the 2030s will finally kill the Rube Goldberg scheme of space solar and its ground rectennas.
Why a SpaceX thread? Because BFR will carry cargos not made by SpaceX. It might even carry cargoes that Elon Musk doesn't approve of.

Personally, I was keen on Space Solar Power as a teenager, decades ago. Then I parked it as "something for after a lunar or asteroid base".

But the point is, with BFR, "launch costs" are no longer an objection. Sure, there are plenty of other hurdles. But if it's to be built, I suspect it'll be a Japanese company buying BFR launches.

Offline alexterrell

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Re: Space Solar Power with BFR
« Reply #11 on: 05/01/2018 02:59 pm »
I assume it's the weather, but 10* is too pessimistic.

Neglecting spectral effects (some of the 1.36kW is not going to be useful) and assuming that's claiming 136W/m^2 average insolation to solar panels. Or put another way, 1191kWh/year.
Multiplying by a possibly optimistic 20% loss, that comes out to 900kWh/m^2/year.

900kWh/m^2 is beaten even in most of Scotland.

In my part of Scotland, fixed panels get 1240kWh/m^2/year, 2 axis trackers 1600.
In more moderate climates (middle of France) it's around 1520kWh/m^2/1990.
And in Arizona/north-Africa like climates, 2110/2960.

In the best climates, with trackers, it's much closer to 3* than 10*.

10* is only gotten in places where people basically don't live.
That is what I thought as well. I have seen similar math exercises and there never was a factor of 10 improvement.
In England, you will normally get 1000KWh per year per KW(peak) of capacity.

In GEO, you will get 365 * 24 = 8,760KWh per year per KW(peak) of capacity.

You will also get more KW(peak) per m2 in space. Maybe not 1.36 times, but certainly more than 1. 

So your solar cells will deliver at least 10 times the energy of solar cells in England. In the months of December and January, when the energy is most needed, they'll deliver about 40 to 60 times as much energy. Northern Europe or Japan would be the most likely target markets.

Offline whitelancer64

Re: Space Solar Power with BFR
« Reply #12 on: 05/01/2018 03:08 pm »
(This might be a topic for elsewhere, but SpaceX might be a game changer for this, to the annoyance of Musk)

Certainly, space solar power has long been dismissed, primarily due to
1. High launch costs (the original idea killer - coupled with falling oil prices)
2. A lack of space capability meaning we can't make the power sats from asteroids or lunar material.

And here is what Musk said, a few year back:
Quote
You see, that's the point I'm making. Take any given solar cell: is it better to have on Earth or in orbit? What do you get from being in orbit? You get twice as much sun, best case. But you've got do do a conversion. You've got incoming photons that go to electrons, but you have to do two conversions you don't have to do on Earth. You've got to convert it to photons and then convert those photons back into electrons.

And that double conversion is going to get you back to where you started basically! So why are you sending them to bloody space?

And by the way, electron to photon converters are not free, nor is sending stuff to space. So then it obviously super-doesn't work.

Case closed! You'd think case closed! But no, I guarantee it's gonna come up another ten times! I mean, for the love of god!

Case closed? Now, I know questioning Musk is unwise these days, but could BFR prove him wrong?

*snip*


You've completely ignored Elon Musk's point: conversion and transmission losses. That's the number one problem with beamed space based solar power.
"One bit of advice: it is important to view knowledge as sort of a semantic tree -- make sure you understand the fundamental principles, ie the trunk and big branches, before you get into the leaves/details or there is nothing for them to hang on to." - Elon Musk
"There are lies, damned lies, and launch schedules." - Larry J

Offline alexterrell

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Re: Space Solar Power with BFR
« Reply #13 on: 05/01/2018 03:18 pm »

You've completely ignored Elon Musk's point: conversion and transmission losses. That's the number one problem with beamed space based solar power.
I specifically covered it. Conversion and transmission losses are much smaller than capacity factor loss. Which is why Space Solar power was originally proposed and studied in the 1960s.

Offline speedevil

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Re: Space Solar Power with BFR
« Reply #14 on: 05/01/2018 03:30 pm »
In England, you will normally get 1000KWh per year per KW(peak) of capacity.

In GEO, you will get 365 * 24 = 8,760KWh per year per KW(peak) of capacity.

You will also get more KW(peak) per m2 in space. Maybe not 1.36 times, but certainly more than 1. 

So your solar cells will deliver at least 10 times the energy of solar cells in England. In the months of December and January, when the energy is most needed, they'll deliver about 40 to 60 times as much energy. Northern Europe or Japan would be the most likely target markets.
More coffee needed - sorry.

Offline whitelancer64

Re: Space Solar Power with BFR
« Reply #15 on: 05/01/2018 03:50 pm »

You've completely ignored Elon Musk's point: conversion and transmission losses. That's the number one problem with beamed space based solar power.
I specifically covered it. Conversion and transmission losses are much smaller than capacity factor loss. Which is why Space Solar power was originally proposed and studied in the 1960s.

Power loss from conversion and transmission through the atmosphere is something like 60%

That's hardly trivial, and it's the cornerstone of why beamed space-based space power is not going to happen anytime soon.

It works out to be about as effecitve to have solar panels on the ground rather than in space, without spending the billions needed to send them there.

That's the entire point Musk is making - and you do not address it at all.
"One bit of advice: it is important to view knowledge as sort of a semantic tree -- make sure you understand the fundamental principles, ie the trunk and big branches, before you get into the leaves/details or there is nothing for them to hang on to." - Elon Musk
"There are lies, damned lies, and launch schedules." - Larry J

Offline aero

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Re: Space Solar Power with BFR
« Reply #16 on: 05/01/2018 04:06 pm »

You've completely ignored Elon Musk's point: conversion and transmission losses. That's the number one problem with beamed space based solar power.
I specifically covered it. Conversion and transmission losses are much smaller than capacity factor loss. Which is why Space Solar power was originally proposed and studied in the 1960s.

Power loss from conversion and transmission through the atmosphere is something like 60%

That's hardly trivial, and it's the cornerstone of why beamed space-based space power is not going to happen anytime soon.

It works out to be about as effecitve to have solar panels on the ground rather than in space, without spending the billions needed to send them there.

That's the entire point Musk is making - and you do not address it at all.

How do those calculations work out for Mars high latitude facilities and for equatorial facilities on the Moon?
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Offline whitelancer64

Re: Space Solar Power with BFR
« Reply #17 on: 05/01/2018 04:19 pm »

You've completely ignored Elon Musk's point: conversion and transmission losses. That's the number one problem with beamed space based solar power.
I specifically covered it. Conversion and transmission losses are much smaller than capacity factor loss. Which is why Space Solar power was originally proposed and studied in the 1960s.

Power loss from conversion and transmission through the atmosphere is something like 60%

That's hardly trivial, and it's the cornerstone of why beamed space-based space power is not going to happen anytime soon.

It works out to be about as effecitve to have solar panels on the ground rather than in space, without spending the billions needed to send them there.

That's the entire point Musk is making - and you do not address it at all.

How do those calculations work out for Mars high latitude facilities and for equatorial facilities on the Moon?

Much better, since there's little atmosphere on Mars and none on the Moon. The problem with the Moon is there are no lunar-stationary orbits, they are unstable because that altitude is outside the Moon's hill sphere. So you'd need a series of solar arrays orbiting the Moon that beam power when in sight of the Lunar station. It makes more sense if you have a lot of locations on the Moon that could benefit from these arrays, but then that becomes a cart-horse issue.
"One bit of advice: it is important to view knowledge as sort of a semantic tree -- make sure you understand the fundamental principles, ie the trunk and big branches, before you get into the leaves/details or there is nothing for them to hang on to." - Elon Musk
"There are lies, damned lies, and launch schedules." - Larry J

Offline alexterrell

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Re: Space Solar Power with BFR
« Reply #18 on: 05/01/2018 04:34 pm »

You've completely ignored Elon Musk's point: conversion and transmission losses. That's the number one problem with beamed space based solar power.
I specifically covered it. Conversion and transmission losses are much smaller than capacity factor loss. Which is why Space Solar power was originally proposed and studied in the 1960s.

Power loss from conversion and transmission through the atmosphere is something like 60%

That's hardly trivial, and it's the cornerstone of why beamed space-based space power is not going to happen anytime soon.

It works out to be about as effecitve to have solar panels on the ground rather than in space, without spending the billions needed to send them there.

That's the entire point Musk is making - and you do not address it at all.

How do those calculations work out for Mars high latitude facilities and for equatorial facilities on the Moon?
In both instances, you have a problem of scale. This only works from about 4GW upwards on Earth.

Mars is better as a Aerostationary orbit is only about half as far as GEO, so you can scale down to 2GW.

The moon is a bit harder as you'd have to go to L1 or L2, which is actually further - I think 60,000km. On the moon, and perhaps Mars, with no/less atmosphere, lasers might be worth looking at. You drop from a DC to DC efficiency of about 60% (for microwaves) to perhaps 20% (for monochromatic lasers and PV cells), but minimum size would be MW rather than GW.

 

Offline alexterrell

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Re: Space Solar Power with BFR
« Reply #19 on: 05/01/2018 04:43 pm »

Power loss from conversion and transmission through the atmosphere is something like 60%

That's hardly trivial, and it's the cornerstone of why beamed space-based space power is not going to happen anytime soon.

It works out to be about as effecitve to have solar panels on the ground rather than in space, without spending the billions needed to send them there.

That's the entire point Musk is making - and you do not address it at all.
The figures I can find suggest efficiency of >70% x >80%, so the loss is about 40%. Musks point is the efficiency loss is about the same as with Earth based solar cells.

The points Musk forgets to mention are capacity factor and intermittency. Developers of solar power like to forget about these factors, but capacity factor in northern Europe is typically 11% over the year and 2.5% in December. Compared to a 60% transmission efficiency?

Offline envy887

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Re: Space Solar Power with BFR
« Reply #20 on: 05/01/2018 06:07 pm »

You've completely ignored Elon Musk's point: conversion and transmission losses. That's the number one problem with beamed space based solar power.
I specifically covered it. Conversion and transmission losses are much smaller than capacity factor loss. Which is why Space Solar power was originally proposed and studied in the 1960s.

Power loss from conversion and transmission through the atmosphere is something like 60%

That's hardly trivial, and it's the cornerstone of why beamed space-based space power is not going to happen anytime soon.

It works out to be about as effecitve to have solar panels on the ground rather than in space, without spending the billions needed to send them there.

That's the entire point Musk is making - and you do not address it at all.

How do those calculations work out for Mars high latitude facilities and for equatorial facilities on the Moon?

Much better, since there's little atmosphere on Mars and none on the Moon. The problem with the Moon is there are no lunar-stationary orbits, they are unstable because that altitude is outside the Moon's hill sphere. So you'd need a series of solar arrays orbiting the Moon that beam power when in sight of the Lunar station. It makes more sense if you have a lot of locations on the Moon that could benefit from these arrays, but then that becomes a cart-horse issue.

EML-1 and EML-2 are lunar-stationary and reasonably stable, if rather far away.

Offline aero

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Re: Space Solar Power with BFR
« Reply #21 on: 05/01/2018 06:25 pm »

You've completely ignored Elon Musk's point: conversion and transmission losses. That's the number one problem with beamed space based solar power.
I specifically covered it. Conversion and transmission losses are much smaller than capacity factor loss. Which is why Space Solar power was originally proposed and studied in the 1960s.

Power loss from conversion and transmission through the atmosphere is something like 60%

That's hardly trivial, and it's the cornerstone of why beamed space-based space power is not going to happen anytime soon.

It works out to be about as effecitve to have solar panels on the ground rather than in space, without spending the billions needed to send them there.

That's the entire point Musk is making - and you do not address it at all.

How do those calculations work out for Mars high latitude facilities and for equatorial facilities on the Moon?
In both instances, you have a problem of scale. This only works from about 4GW upwards on Earth.

Mars is better as a Aerostationary orbit is only about half as far as GEO, so you can scale down to 2GW.

The moon is a bit harder as you'd have to go to L1 or L2, which is actually further - I think 60,000km. On the moon, and perhaps Mars, with no/less atmosphere, lasers might be worth looking at. You drop from a DC to DC efficiency of about 60% (for microwaves) to perhaps 20% (for monochromatic lasers and PV cells), but minimum size would be MW rather than GW.

Mars is better as a Aerostationary orbit is only about half as far as GEO, so you can scale down to 2GW.

How is that calculated? I would naively think that the inverse square law would apply giving a scale factor of 1/4. One GW is still huge though.
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Offline alexterrell

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Re: Space Solar Power with BFR
« Reply #22 on: 05/01/2018 07:11 pm »
As a rule of thumb I recall:

Antenna diameter x Receiver diameter > wavelength x distance

Hence you are stuck with big diameters for microwaves, and hence lots of power. With Mars, you could halve the diameter of the ground station, and hence quarter the power.

Of course, there are variables to play with. On Mars, there may be higher microwave frequencies that can still be produced efficiently, but would not penetrate Earth's atmosphere (that is also one reason lasers can be contemplated on Mars, but not Earth).

You can of course reduce the power, but then the antenna / rectenna costs rise per unit of electricity. And of course, on Mars, with no birds or planes to worry about, you could increase the power density.

For Mars or moon, I'd start with lasers till demand gets up to 0.5 to 1GW. You could even use lasers to power individual (though big) mining and exploration trucks.

Offline rickyramjet

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Re: Space Solar Power with BFR
« Reply #23 on: 05/01/2018 07:37 pm »
Apologies to the OP, but IMO spaced based power will never make sense.  Even if you could transport it to space for free. 

1.  The size of a 6GW (the OP's choice) array will be approx (assume 20% cell efficiency, so 272 watts/meter sq) > 22 million sq meters or roughly 8.5 sq miles.  Or to make my point about the size, it's about 4000 football fields.
2.  What structure supports that monster array to keep it rigid?
3.  How do you keep the array pointed at the sun, without twisting and warping it?  Does it use fuel?  How long does the fuel last?  Seems like you'd need hundreds of thrusters.  What if one of them sticks on?
4.  How do you feed all that power to a microwave transmitter, which must be pointed in a constantly moving and different direction from the array?  Even if you can use a phased array antenna, it's still a massive thing!
5.  How do you repair it when it gets hit by micrometeorites or simply fails?
6.  How do you protect it from a large solar flare?
7.  And, if we want a 20 year life, don't the panels need to be made from gallium arsenide?  I recall silicon panels degrade rapidly in space.

Even if you build smaller arrays it is still a space based construction task of a size that would dwarf all other space based projects ever done.  Remember all the issues the ISS has had with their arrays?  And that is tiny by comparison.

On Earth, construction is easy.  It doesn't require men in space suits or advanced robotics (that don't yet exist).  Look how fast the array (admittedly small) in Boca Chica was installed by basic electricians in an unprepared field.  On Earth, if a panel or system fails, some technician in a rusty Ford F150 wearing a t-shirt and jeans fixes the problem in 30 minutes.  On Earth, solar panels can be localized, as in individual buildings and home.  You don't need a huge antenna in an isolated desert somewhere.

Just my 2 cents.

Offline RonM

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Re: Space Solar Power with BFR
« Reply #24 on: 05/01/2018 08:33 pm »
I'm not an electrical engineer and so am out of my depth when discussing antenna dimensions, but is there any way to use a smaller antenna?  How does antenna diameter relate to electrical power, and to distance, and the size of the receiving rectenna?

The microwave antenna and rectenna are large for safety reasons. Sure they can be smaller, but the environmental impact study will be unkind if the power transmission system cooks birds as soon as the fly into the beam. Also has the nasty potential as a weapon system.

Offline CuddlyRocket

Re: Space Solar Power with BFR
« Reply #25 on: 05/01/2018 09:11 pm »
I suspect Elon and SpaceX's attitude to a space-based solar-power satellite will be that they're not going to build one but if someone else wants to do so then they'll sell them the transportation to get their equipment into space - payable on delivery!

On Earth, solar panels can be localized, as in individual buildings and home.  You don't need a huge antenna in an isolated desert somewhere.

The receiving antenna will effectively be a power station embedded in a local or wider grid and therefore there will be distribution losses; with solar cells on the roofs of houses or factories etc, not so much.

The advantage of consistent 24-hr supply can be overstated as there is not consistent 24-hr demand for electricity; night-time demand is a lot lower than daytime. Also, there are other sources of electricity at night (wind and hydro being the obvious renewable ones). Both factors lower the amount of storage needed. One should also note that daytime electricity is worth more than night-time!

But it would be interesting to see a financial calculation. One would surmise that the first solar power satellite will be regarded as a riskier investment than ground-based solar, which is well understood. The rewards need to be commensurate!

Offline Patchouli

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Re: Space Solar Power with BFR
« Reply #26 on: 05/01/2018 09:30 pm »
NASA has done a short range transmission with 82% efficiency back in the 1970s for larger distances the receiver would have to be larger.


One big issue with ground solar is the land under solar panels can't be used for anything else other than maybe parking if they're not roof mounted.
 But the ground under a rectenna array can still be used for farming as sun light and rain would just pass through while the microwaves won't.
« Last Edit: 05/01/2018 09:36 pm by Patchouli »

Online TrevorMonty

Re: Space Solar Power with BFR
« Reply #27 on: 05/01/2018 10:29 pm »
Elon views are also biased given his financial interests in Solarcity and Tesla batteries.

Terrestrial solar systems have a place but they are limited by climate and seasons. Great in sunny locations but useless in northern and southern winters.

We need long term green solution to power generation. Fusion and SSP are only ones that can generate huge amounts of power need in the next few decades. Neither is proven, fusion is still an unknown, SSP is technically feasible, but needs lot more work and flying demo.

Economically SSP is not viable if everything needs to be lifted from earth to GEO. Needs in space manufacturing, assembly and  ISRU for both construction materials and fuel to reduce LEO to GEO transport costs. Ideally bulk mass is ISRU with high tech equipment coming from earth. The good news is in space robotic assembly and manufacturing is being worked on.
With large telescopes and persistant platforms in GEO being initial uses for these technologies.







Offline biosehnsucht

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Re: Space Solar Power with BFR
« Reply #28 on: 05/01/2018 11:14 pm »
Actually you can do agriculture under solar too. https://cleantechnica.com/2017/11/24/combining-solar-panels-agriculture-makes-land-productive/

You can also float panels on water https://cleantechnica.com/2017/12/13/china-powers-worlds-largest-floating-solar-power-plant/

And obviously, you can place them on structures which care not if there is sunlight on the top (homes, business, etc) - arguably in many places the less solar on the roof the better (solar > power is good, solar > heat that must be removed by HVAC is bad)

Offline speedevil

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Re: Space Solar Power with BFR
« Reply #29 on: 05/01/2018 11:24 pm »
We need long term green solution to power generation. Fusion and SSP are only ones that can generate huge amounts of power need in the next few decades. Neither is proven, fusion is still an unknown, SSP is technically feasible, but needs lot more work and flying demo.

Economically SSP is not viable if everything needs to be lifted from earth to GEO. Needs in space manufacturing, assembly and  ISRU for both construction materials and fuel to reduce LEO to GEO transport costs. Ideally bulk mass is ISRU with high tech equipment coming from earth.
If ISRU for propellant works for LNG production on Mars at 50% efficiency, that sets a floor on the price of electricity to a degree, even without SSP or fusion in that it makes storage and transport of 'solar' energy plausible.
Batteries and modest overprovision locally, as well as long distance interconnectors (possibly superconductor) also help.


Hybrid approaches may be interesting.
For GEO, you need really high powers and large satellites.
This is pretty much needed so you can have power at night.

If batteries are good enough, on the ground, you might be able to consider very much smaller satellites at - say - 1400km, which charge places where it's not been sunny, or is winter, as they fly overhead.

Offline Ludus

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Re: Space Solar Power with BFR
« Reply #30 on: 05/01/2018 11:49 pm »
I think there might be some reasons that SpaceSolar has commercial advantages for Mars settlement that don’t apply on earth.

On earth Elon’s main point is you’re adding a lot to the cost of solar PV by lifting it into Space and you’re putting up with conversion and transmission losses too.

On Mars if you’re looking at it as a business to sell power, the first point doesn’t apply. You have to ship everything to Mars anyway. If you ship whole Solar Power Sats ready to deploy to Areostationary orbit, overall costs might even be lower than equivalent power plants shipped to the surface.

You can sell power on a constant basis greatly reducing the need to ship a lot of mass of batteries too.

You can plan independently of settlement details. A power sat can sell power to most locations on Mars surface. You just have to bet there will be a market for your power to start designing and building power sats.

If there are unexpected finds and people want to set up new outposts to exploit them, you’re ready to sell them power.

On the surface, PV would require more upkeep because of sand and dust than rectennas. PV is easier to deploy and fully automate in space.

Areostationary orbit is just 10,583 miles from the surface so less than half the distance for earth.

It’s a pretty automated business that sells a billable service very likely to be valuable to anybody settling Mars. There aren’t any compatibility issues. There aren’t that many things you could invest in now you could be reasonably confident would lead to sales if Mars is settled.
« Last Edit: 05/02/2018 12:24 am by Ludus »

Offline Robotbeat

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Re: Space Solar Power with BFR
« Reply #31 on: 05/01/2018 11:59 pm »
I don't understand how you get to 10 times more in orbit than on the ground. The solar intensity at 1 AU is 1.36 kW. On the ground it is about 1 kW, depending on where you are, the weather, etc.

Because capacity factors for fixed solar on the ground are between about 0.1 (Germany, England) and 0.2 (Atacama desert).
...
Wrong. The American Southwest has statewide<[ capacity factors of about 26%. Parts of Chile are even higher.

Using Germany as an example is a red herring. It’s a terrible place for solar power. The vast majority of the world’s population and surface area gets vastly more sunlight.
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Offline ulm_atms

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Re: Space Solar Power with BFR
« Reply #32 on: 05/02/2018 01:14 am »
Two things....

1.  I am enjoying reading this thread.  It's nice to have the issues/math laid out.

2.  Would this not be better in the Advanced Concepts section since, except for Musk's quote and the fact that BFS might be the only ship to pull it off if deemed economical, has nothing to really do with SpaceX?

Thanks for the read so far!

Online TrevorMonty

Re: Space Solar Power with BFR
« Reply #33 on: 05/02/2018 03:26 am »
Two things....

1.  I am enjoying reading this thread.  It's nice to have the issues/math laid out.

2.  Would this not be better in the Advanced Concepts section since, except for Musk's quote and the fact that BFS might be the only ship to pull it off if deemed economical, has nothing to really do with SpaceX?

Thanks for the read so far!
Its nice change, typically its SpaceX that overtakes a nonSpaceX thread.

Offline Lar

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Re: Space Solar Power with BFR
« Reply #34 on: 05/02/2018 05:15 am »
What I think is cool is that it doesn't matter whether Musk thinks it's a good idea or not.  The market will decide, someone will pay the BFS launch costs to try and we'll all find out.
"I think it would be great to be born on Earth and to die on Mars. Just hopefully not at the point of impact." -Elon Musk
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Offline alexterrell

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Re: Space Solar Power with BFR
« Reply #35 on: 05/02/2018 07:46 am »
Apologies to the OP, but IMO spaced based power will never make sense.  Even if you could transport it to space for free. 

1.  The size of a 6GW (the OP's choice) array will be approx (assume 20% cell efficiency, so 272 watts/meter sq) > 22 million sq meters or roughly 8.5 sq miles.  Or to make my point about the size, it's about 4000 football fields.
2.  What structure supports that monster array to keep it rigid?
3.  How do you keep the array pointed at the sun, without twisting and warping it?  Does it use fuel?  How long does the fuel last?  Seems like you'd need hundreds of thrusters.  What if one of them sticks on?
4.  How do you feed all that power to a microwave transmitter, which must be pointed in a constantly moving and different direction from the array?  Even if you can use a phased array antenna, it's still a massive thing!
5.  How do you repair it when it gets hit by micrometeorites or simply fails?
6.  How do you protect it from a large solar flare?
7.  And, if we want a 20 year life, don't the panels need to be made from gallium arsenide?  I recall silicon panels degrade rapidly in space.

Even if you build smaller arrays it is still a space based construction task of a size that would dwarf all other space based projects ever done.  Remember all the issues the ISS has had with their arrays?  And that is tiny by comparison.

On Earth, construction is easy.  It doesn't require men in space suits or advanced robotics (that don't yet exist).  Look how fast the array (admittedly small) in Boca Chica was installed by basic electricians in an unprepared field.  On Earth, if a panel or system fails, some technician in a rusty Ford F150 wearing a t-shirt and jeans fixes the problem in 30 minutes.  On Earth, solar panels can be localized, as in individual buildings and home.  You don't need a huge antenna in an isolated desert somewhere.

Just my 2 cents.
All of the issues you raise are challenges, and have been addressed in various studies since the 1960s. The biggest challenge was launch costs making the whole thing uneconomic, and SpaceX are addressing that challenge (aided by solar power getting lighter).

The various studies look at your questions, but here's my thoughts:
1. Yes
2. The original proposal was "beam builders". A section trusses to support a 50km2, 100,000 ton structure. I assume they calculated the stresses. It's not what you'd call "rigid" on Earth, but fine at 42,000km. I would suggest the solar sheet is thin fabric, stretched over a frame in 1km x 1km squares.
3. I'd suggest electric ion thrusters (which would also move the sections from LEO to GEO). The thing has to rotate every 24 hours, and that keeps it rigid. Probably some dispersed gyros for micro control.
4. That is a tricky bit, and the bit I missed was a 6GW commutator. The Jaxo design (https://spectrum.ieee.org/green-tech/solar/how-japan-plans-to-build-an-orbital-solar-farm) gets around this by having rotating mirrors reflect light on to the array. I think I still prefer the original Glaser designs of 1968.
5. Micrometeorites would just go through the sheets like they would through aluminium foil. That would degrade the capability over the course of millennia.
6. Solar flare: Do you mean the power carrying cables which would have a current induced in them? Not sure.
7. Various thin films are being discussed. I think if this thing is put up, it should have a multi decade life - disposal / recycling will be a big issue I haven't seen discussed in the literature.

Is construction easy on Earth? At some point, we need to challenge the idea that it's harder in space. It needs to be easier, and indeed, in space, you can move structures weighing 100 tons and spanning 1 square kilometre, and join them up. On Earth, it would be blown away by the wind or collapse under gravity.

Offline alexterrell

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Re: Space Solar Power with BFR
« Reply #36 on: 05/02/2018 07:51 am »
I don't understand how you get to 10 times more in orbit than on the ground. The solar intensity at 1 AU is 1.36 kW. On the ground it is about 1 kW, depending on where you are, the weather, etc.

Because capacity factors for fixed solar on the ground are between about 0.1 (Germany, England) and 0.2 (Atacama desert).
...
Wrong. The American Southwest has statewide<[ capacity factors of about 26%. Parts of Chile are even higher.

Using Germany as an example is a red herring. It’s a terrible place for solar power. The vast majority of the world’s population and surface area gets vastly more sunlight.
Probably the idea of using solar as any example is wrong. Space Solar power competes with nuclear fusion as a clean method of providing base load (or even peaking) power.

Solar might be useful in the tropics, but will always be a marginal player in northern latitudes, which is why Europe is actually a better example. Europe will need nuclear fission, nuclear fusion, or space solar power.

Offline alexterrell

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Re: Space Solar Power with BFR
« Reply #37 on: 05/02/2018 07:53 am »
Two things....

1.  I am enjoying reading this thread.  It's nice to have the issues/math laid out.

2.  Would this not be better in the Advanced Concepts section since, except for Musk's quote and the fact that BFS might be the only ship to pull it off if deemed economical, has nothing to really do with SpaceX?

Thanks for the read so far!
Thanks. It probably should be moved to Advanced.

Originally I wanted to address Musk's erroneous statements and ask whether BFR could enable Space Solar Power, rather than discuss the merits of Space Solar Power.

Offline alexterrell

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Re: Space Solar Power with BFR
« Reply #38 on: 05/02/2018 07:58 am »
I suspect Elon and SpaceX's attitude to a space-based solar-power satellite will be that they're not going to build one but if someone else wants to do so then they'll sell them the transportation to get their equipment into space - payable on delivery!

On Earth, solar panels can be localized, as in individual buildings and home.  You don't need a huge antenna in an isolated desert somewhere.

The receiving antenna will effectively be a power station embedded in a local or wider grid and therefore there will be distribution losses; with solar cells on the roofs of houses or factories etc, not so much.

The advantage of consistent 24-hr supply can be overstated as there is not consistent 24-hr demand for electricity; night-time demand is a lot lower than daytime. Also, there are other sources of electricity at night (wind and hydro being the obvious renewable ones). Both factors lower the amount of storage needed. One should also note that daytime electricity is worth more than night-time!

But it would be interesting to see a financial calculation. One would surmise that the first solar power satellite will be regarded as a riskier investment than ground-based solar, which is well understood. The rewards need to be commensurate!
If several Solar Stations are built, they could provide dozens of ground stations - basically following the demand curve. They could beam North in winter to provide heating, and south in Summer to provide Air-con. The only limitation is how much investment is made in the ground stations.

Storage to cover renewables might be feasible in Arizona, but not in places like the UK. There, gas is the chosen backup fuel (and coal in Germany).

Offline alexterrell

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Re: Space Solar Power with BFR
« Reply #39 on: 05/02/2018 08:06 am »
I'm not an electrical engineer and so am out of my depth when discussing antenna dimensions, but is there any way to use a smaller antenna?  How does antenna diameter relate to electrical power, and to distance, and the size of the receiving rectenna?

The microwave antenna and rectenna are large for safety reasons. Sure they can be smaller, but the environmental impact study will be unkind if the power transmission system cooks birds as soon as the fly into the beam. Also has the nasty potential as a weapon system.
Not quite. You can make the Earth receiver smaller (for a given transmission frequency) only by making the space transmitter bigger. That would then concentrate the microwaves to a higher density. I would suggest a legal maximum size of transmitter and power, which would physically limit the beam intensity. (Probably to 1KW/m2).

That way, the only way a SF writer can conjure up death rays, would be by taking over multiple Solar Power Sats and pointing them all at the White House at the same time. (In which case, the President would need to shelter under some aluminium foil).

Offline speedevil

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Re: Space Solar Power with BFR
« Reply #40 on: 05/02/2018 10:12 am »
Solar might be useful in the tropics, but will always be a marginal player in northern latitudes, which is why Europe is actually a better example. Europe will need nuclear fission, nuclear fusion, or space solar power.

That rather depends on if interconnect is a thing, and 'europe' varies dramatically.
As a consumer, I am paying $0.18/kWh.
Solar panel prices are at around $0.5/W.

Five years worth of power at this price will buy me 7.5kWp of solar panels.

This provides me 9 months of the year or so with a power surplus.
Combining this with daily thermal storage for heating and 3kWh or so of batteries to cover nighttime loads, and this will cover 80%+ of my incoming power bill, for an investment of around 7 years worth of power bills.

If I was in London, it adds another month to independance (as well as having a very large daily surplus in the summer).

I am not here counting export to the grid at all.

I am not counting costs other than panels or batteries., which balances the above out somewhat.

Solar+battery is at a price where for large installations, over the whole lifetime of the system it is somewhat comparable with the price paid to generators for baseload power. ($70/MW). Extra supply would be needed here 3 months of the year.


Offline Robotbeat

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Re: Space Solar Power with BFR
« Reply #41 on: 05/02/2018 11:12 am »
Northern Europe is just a small portion of the world’s population. The vast majority have good access to solar and could rely entirely on it. Not just “maybe in the tropics.”

I agree space based solar power is currently more realistic than fusion.
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Offline AncientU

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Re: Space Solar Power with BFR
« Reply #42 on: 05/02/2018 01:19 pm »
I'm not an electrical engineer and so am out of my depth when discussing antenna dimensions, but is there any way to use a smaller antenna?  How does antenna diameter relate to electrical power, and to distance, and the size of the receiving rectenna?

The microwave antenna and rectenna are large for safety reasons. Sure they can be smaller, but the environmental impact study will be unkind if the power transmission system cooks birds as soon as the fly into the beam. Also has the nasty potential as a weapon system.
Not quite. You can make the Earth receiver smaller (for a given transmission frequency) only by making the space transmitter bigger. That would then concentrate the microwaves to a higher density. I would suggest a legal maximum size of transmitter and power, which would physically limit the beam intensity. (Probably to 1KW/m2).

That way, the only way a SF writer can conjure up death rays, would be by taking over multiple Solar Power Sats and pointing them all at the White House at the same time. (In which case, the President would need to shelter under some aluminium foil).

That's an awful lot of expense to get surface power equal to what the sun delivers for free.
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Offline alexterrell

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Re: Space Solar Power with BFR
« Reply #43 on: 05/02/2018 02:55 pm »

That's an awful lot of expense to get surface power equal to what the sun delivers for free.
It's a lot more than the sun delivers for free.

In northern Europe, about 30 times more electricity than the sun delivers. (Solar capacity factor of 10%, and 3 times the conversion efficiency).

Add to that the fact that the Rectenna is much cheaper than solar panels, and still allows light through which can be used for agriculture.

Then add to that the fact that the sun only delivers the power some of the time, and quite rarely in winter, to the extent that the solar has zero capacity value.

Online Semmel

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Re: Space Solar Power with BFR
« Reply #44 on: 05/02/2018 07:51 pm »
The question for efficiency and cost effectiveness is one thing. But there are other questions..

Maybe the most serious question with solar power is.. what do you do with all the grilled birds that fly through the beam? Or the aircraft that get zapped? Or if the beam wonders off for some reason and starts a huge forest fire or cooks a small town by mistake? Or.. what would the $political_enemy_of_choice think if you start building giant orbital microwave beam weapons? "They are totally for civilian use only!" you say?

Sorry, that got out of hand fast. What I mean is, there are tons of considerations besides efficiency and cost that are very serious.

Offline speedevil

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Re: Space Solar Power with BFR
« Reply #45 on: 05/02/2018 08:30 pm »
The question for efficiency and cost effectiveness is one thing. But there are other questions..

Maybe the most serious question with solar power is.. what do you do with all the grilled birds that fly through the beam?
Some of these can be mitigated by design choices.
If your space power sat is at GEO, and has its antenna and solar panels the same size, if it is under xGW, for a given frequency, the power onto earth can't exceed 1kW/m^2 or whatever limit you think appropriate.
More involved schemes are possible.

Online Semmel

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Re: Space Solar Power with BFR
« Reply #46 on: 05/02/2018 08:51 pm »
The question for efficiency and cost effectiveness is one thing. But there are other questions..

Maybe the most serious question with solar power is.. what do you do with all the grilled birds that fly through the beam?
Some of these can be mitigated by design choices.
If your space power sat is at GEO, and has its antenna and solar panels the same size, if it is under xGW, for a given frequency, the power onto earth can't exceed 1kW/m^2 or whatever limit you think appropriate.
More involved schemes are possible.

If you had such a large beam, you would need a large receiver as well. Why would you need a satellite in the first place?

Offline RyanC

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Re: Space Solar Power with BFR
« Reply #47 on: 05/02/2018 08:51 pm »
It's feasible.

But for MILITARY applications.

https://www.serdp-estcp.org/content/download/8524/104509/file/FOB_Report_Public.pdf

Quote
Al‐Asad (Iraq) includes 20,000 people living on 18 square miles, with an internal bus system, 48 1
megawatt (MW) generators, 32 MW of continuous power demand, 1.1m gallons of water/day demand,
1.2m gallons of water/day supply, 9 water wells, Reverse Osmosis Water Purification Unit (ROWPU),
water treatment facilities treating 60 gallons/person/day, 6,771 facilities, and 193 spot generators


...


A 600 soldier FOB requires a convoy of 22 trucks per day to supply the base with fuel or water
and to truck away wastewater and solid waste

...

As of November 2007, 80 convoys were continuously
traveling between Kuwait and Iraq (with 70% transporting fuel or water), exposing a critical vulnerability
to Improvised Explosive Devices (IEDs) as they transported supplies from surrounding nations.

...

FOB Planning Factors:

500 man base camp -- 182 kW
1,500 man " " -- 486 KW
3,000 man " " -- 988 KW
10,000 man " " -- 3,293 KW

...

The USMC Energy Assessment team calculated the contractor delivered fuel to Camp
Leatherneck in Afghanistan at $6.39 per gallon, and $11.70 per gallon to deliver the fuel to the tactical
edge (FOB Dwyer, 50 kilometers from Camp Leatherneck).148  An earlier estimate puts FY 02 standard
DESC fuel price at $1.34 per gallon, a “true cost” of USAF tanker‐delivered fuel at $17.50 per gallon, and
“hundreds of dollars per gallon for Army forces deep in the battlespace.”

With all that cost; it's practically cheap to deploy a 10 MW Solar Power Satellite to beam 9MW into remote forward operating bases -- you can use that excess "free" energy to run "moisture farms", basically, use air conditioningn units in reverse to capture the moisture in the air to make water.

Offline CuddlyRocket

Re: Space Solar Power with BFR
« Reply #48 on: 05/02/2018 09:15 pm »
You can sell power on a constant basis greatly reducing the need to ship a lot of mass of batteries too.

You can plan independently of settlement details. A power sat can sell power to most locations on Mars surface. You just have to bet there will be a market for your power to start designing and building power sats.

If there are unexpected finds and people want to set up new outposts to exploit them, you’re ready to sell them power.

On the surface, PV would require more upkeep because of sand and dust than rectennas. PV is easier to deploy and fully automate in space.

You'll probably have to deal with your potential customers concerns as to reliability. After all, if they lose power they're dead! Surface PV might need more upkeep, but is unlikely to go down all at once and access for repair is easier.

Solar might be useful in the tropics, but will always be a marginal player in northern latitudes, which is why Europe is actually a better example. Europe will need nuclear fission, nuclear fusion, or space solar power.

Days are long at higher latitudes in summer and winters are wet and windy. Solar power might be a smaller resource but it's still large - it all depends on the cost, which is rapidly declining.

Originally I wanted to address Musk's erroneous statements and ask whether BFR could enable Space Solar Power, rather than discuss the merits of Space Solar Power.

Any launch vehicle that lowers the cost of access to space would make space solar power more financially feasible. Whether the BFR sufficiently lowers that cost requires a financial calculation (which includes how much power an investment of similar amount in ground-based solar would produce).

Offline RonM

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Re: Space Solar Power with BFR
« Reply #49 on: 05/02/2018 09:16 pm »
Attached is a NASA study titled "Satellite Power Systems (SPS) Concept Definition Study" done by Rockwell in 1980.

Page 14 states "power output must be decreased to satisfy the 23 mW/cm2 (0.23 kW/m2) RF energy constraint in the atmosphere to avoid potential microwave interference with the D and F layers of the atmosphere." Seems to be an issue with microwave power transmission through the ionosphere.

Offline Robotbeat

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Re: Space Solar Power with BFR
« Reply #50 on: 05/03/2018 12:26 am »

That's an awful lot of expense to get surface power equal to what the sun delivers for free.
It's a lot more than the sun delivers for free.

In northern Europe...
Northern Europe is a corner case. Ultimately, a niche with less than 20% of the world's population.


...and the same problem Northern Europe has with sunlight is also a problem for space based solar to a large degree. For a geosynchronous solar power satellite, they need a receiver on the ground about twice that of the same angular spot size as on the equator (or, if beam areal energy is the constraint, it still needs to be nearly twice as big as the equator one as the beam is more concentrated in the air than it is on the angle it hits on the ground). It also passes through almost twice as much atmosphere and is thus more sensitive to weather.
« Last Edit: 05/03/2018 12:49 am by Robotbeat »
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Offline alexterrell

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Re: Space Solar Power with BFR
« Reply #51 on: 05/03/2018 10:55 am »
Northern Europe has about 30-50% of the world's demand for clean energy. Partly as a result, electricity is about double the price compared to the USA. If some one does space solar power, Europe or Japan will be the initial target markets, as competing with coal and gas in the USA and hydro in Canada is not easy.

Western Europe uses about 300GW of electricity. That's enough to get going. Whilst the first Powersat is going to be very expensive (perhaps unaffordable so), subsequent ones would be a lot cheaper. 

As for Rectenna size, it would be need to be double sized at 60 degrees North, compared to the Equator. Potential sites might be Thames Estuary (52N), offshore near Copenhagen (55N), in Osaka Bay or Tokyo Bay (Japan 35N).

It might even be an idea (Musk would like this ) to ditch the solar panels and just have the rectenna receiver.  Then beam from the Sahara to New York for their morning demand, and from Arizona to London for their evening demand. But I think if you're going to put this infrastructure in orbit, you might well add the solar panels.

Offline alexterrell

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Re: Space Solar Power with BFR
« Reply #52 on: 05/03/2018 11:41 am »
Attached is a NASA study titled "Satellite Power Systems (SPS) Concept Definition Study" done by Rockwell in 1980.

Page 14 states "power output must be decreased to satisfy the 23 mW/cm2 (0.23 kW/m2) RF energy constraint in the atmosphere to avoid potential microwave interference with the D and F layers of the atmosphere." Seems to be an issue with microwave power transmission through the ionosphere.

Good study. It shows the system was feasible, with problems, with 1980s technology. It would be nice to update it to current tech.

Regarding the atmosphere:
http://www.radio-electronics.com/info/propagation/common/atmosphere.php
It seems that a high density of radiation will ionise particles, which then block radio waves. However, this can't be the whole story because most radiation is coming from the sun (1.3KW/m2), so why would a weaker microwave signal make this worse?

It does say:
Quote
The main effect of the D region is to attenuate signals that pass through it, although the level of attenuation decreases with increasing frequency.
So it might be better to go to >5GHz signal. That reduces the transmitter size, which increases the heat problems.

The efficiency chain was interesting
http://prntscr.com/jd69bu

and they reckoned 30,000 tons: http://prntscr.com/jd69zl

Even with BFR prices, that mass would need to come down a lot.


Offline Robotbeat

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Re: Space Solar Power with BFR
« Reply #53 on: 05/03/2018 12:51 pm »
Northern Europe has about 30-50% of the world's demand for clean energy. Partly as a result, electricity is about double the price compared to the USA.
The world is growing, by the end of this century demand for energy is likely to be roughly proportional to population, making northern Europe niche. And the US has cleaner energy than much of Europe, such as Germany, but much lower prices (because Germany has particularly non-optimal clean energy policy combined with low sun).

Again, Northern Europe is not an appropriate benchmark for global clean energy. And is a bad target for space solar power as well due to the high latitude.
« Last Edit: 05/03/2018 12:55 pm by Robotbeat »
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Offline Robotbeat

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Re: Space Solar Power with BFR
« Reply #54 on: 05/03/2018 12:53 pm »
Attached is a NASA study titled "Satellite Power Systems (SPS) Concept Definition Study" done by Rockwell in 1980.

Page 14 states "power output must be decreased to satisfy the 23 mW/cm2 (0.23 kW/m2) RF energy constraint in the atmosphere to avoid potential microwave interference with the D and F layers of the atmosphere." Seems to be an issue with microwave power transmission through the ionosphere.

Good study. It shows the system was feasible, with problems, with 1980s technology. It would be nice to update it to current tech.

Regarding the atmosphere:
http://www.radio-electronics.com/info/propagation/common/atmosphere.php
It seems that a high density of radiation will ionise particles, which then block radio waves. However, this can't be the whole story because most radiation is coming from the sun (1.3KW/m2), so why would a weaker microwave signal make this worse?

It does say:
Quote
The main effect of the D region is to attenuate signals that pass through it, although the level of attenuation decreases with increasing frequency.
So it might be better to go to >5GHz signal. That reduces the transmitter size, which increases the heat problems.

The efficiency chain was interesting
http://prntscr.com/jd69bu

and they reckoned 30,000 tons: http://prntscr.com/jd69zl

Even with BFR prices, that mass would need to come down a lot.
30,000 tons at $10/kg (BFR pricing) is just $300 million. Not bad for 4Gigawatts to the grid. The mass is fine. It isn’t the constraining factor.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline alexterrell

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Re: Space Solar Power with BFR
« Reply #55 on: 05/03/2018 04:21 pm »
Northern Europe has about 30-50% of the world's demand for clean energy. Partly as a result, electricity is about double the price compared to the USA.
The world is growing, by the end of this century demand for energy is likely to be roughly proportional to population, making northern Europe niche. And the US has cleaner energy than much of Europe, such as Germany, but much lower prices (because Germany has particularly non-optimal clean energy policy combined with low sun).

Again, Northern Europe is not an appropriate benchmark for global clean energy. And is a bad target for space solar power as well due to the high latitude.
At some point, the whole world should aim for European levels of power consumption.

Northern Europe is an excellent initial target market because of high electricity prices, an appetite for clean energy, and not much land space or sun to generate the clean energy. With the possible exception of Japan, there is no where better.

https://www.ovoenergy.com/guides/energy-guides/average-electricity-prices-kwh.html - go for anything over 20 cents per KWh.

Latitude is not problem. It just means elongating the receiver a bit.

And the US has cleaner electricity than EU countries like Poland, Malta, Latvia and Estonia.

Offline Athrithalix

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Re: Space Solar Power with BFR
« Reply #56 on: 05/04/2018 01:40 pm »
One of the most believable current proposals for bringing solar energy on a large scale to Europe is by connecting mega-grids to the MENAT (Middle East, North Africa, and Turkey) region, where huge amounts of investment and technology development are going into solar farms. Given that this is the current direction that green energy in Europe is likely to take, the question for the BFR providing us with space solar power, is can it make SSP cheaper than connecting our grids across to Morocco and Arabia?
It's not really competing with large scale solar power on the ground in Europe, as at that point it's better to use large solar farms further South than to build them in our rainy lands.

Offline tdperk

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Re: Space Solar Power with BFR
« Reply #57 on: 05/04/2018 02:26 pm »
Quote from: ElonMusk
Take any given solar cell: is it better to have on Earth or in orbit? What do you get from being in orbit? You get twice as much sun, best case.

Actually it is at minimum threefold, and with the vagaries of weather in most terrestrial locations, more like four fold.

Ironically, it is a similar multiplier to how much more efficient the energy in a battery EV like the Tesla can be used compared to the stored energy in a tank of gasoline in an IC car.

Offline tdperk

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Re: Space Solar Power with BFR
« Reply #58 on: 05/04/2018 02:27 pm »
At some point, the whole world should aim for European levels of power consumption.

Why should we endorse that relative level of poverty as a goal?

Offline oldAtlas_Eguy

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Re: Space Solar Power with BFR
« Reply #59 on: 05/04/2018 05:34 pm »
The key to th business case is the amount of land used for solar cells vs rectenna to deliver the same total MWh per year or day average. The case for SSPS  is that the land usage is less because the total MWh per Km^2 over a day is higher with a rectenna than with solar cells. That is because the conversion efficiency of the rectenna to received microwaves is much higher >85% vs the conversion efficiency of solar of at peak of 40% for the best cells available but that has to be multiplied by the available sun over the day average  per year of just ~30% so the best conversion and output per m^2 for solar cells is 12% of the peak solar influx. Then add to that the battery energy storage efficiency for 66% of the energy gathered is about 85% reduces the system efficiency of solar peak energy available and delivered to the grid of 10.8%. This the best currently possible. This then for the received solar influx produces 4.5MWh of power per Km^2 of area on average per hour to the grid.

A rectenna converts at 85% and has no fluctuation in available incoming power. No battery storage. So at .23KW per m^2 that is for 1 Km^2 a value of 195 MWh of power per Km^2 of area on average per hour to the grid.

The land usage is a factor of 195/4.5 = ~43

For solar cells on surface to produce 1 GW  average output / hour requires at least 222Km^2 of area.

For rectenna on surface to produce 1GW average output /hour requires about (includes a triple amount for a protective non used or fading out power density ring surrounding the rectenna) of ~ 15 Km^2 of area.

Land on Earth is at a premium. You need to have these massive facilities as close to where the power is to be used to reduce the transmission loss through the wires. Finding 15 to 75 Km^2 (1GW to 5GW average daily output/hour) is much easier that trying to find 222 to 1,110 Km^2 (1GW to 5GW avergae daily output/hour).

Even if the costs per GWh produced is the same for ground solar and SSPS, the SSPS system will win out just because of land usage. Surface solar will still be used but will be an augmentation and not the prime power source for industry and inclement weather. The surface solar will be more of a implementation of usage on available sunward facing rooftops.

Added:
NOTE - For those worried about getting cooked the .23W/cm^2 is less than that produced by your cellphone of 1W/cm^2 next to your head.
« Last Edit: 05/04/2018 06:12 pm by oldAtlas_Eguy »

Offline johnfwhitesell

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Re: Space Solar Power with BFR
« Reply #60 on: 05/04/2018 08:20 pm »
I don't understand how you get to 10 times more in orbit than on the ground. The solar intensity at 1 AU is 1.36 kW. On the ground it is about 1 kW, depending on where you are, the weather, etc.

Because capacity factors for fixed solar on the ground are between about 0.1 (Germany, England) and 0.2 (Atacama desert).
...
Wrong. The American Southwest has statewide<[ capacity factors of about 26%. Parts of Chile are even higher.

Using Germany as an example is a red herring. It’s a terrible place for solar power. The vast majority of the world’s population and surface area gets vastly more sunlight.

A capacity factor of 26% would mean 8.1 kWh/sq-m per day by my math (1.3*24*.26).
This map shows that New Mexico is generally pretty close to that level but slightly shy:
https://www.nrel.gov/gis/images/state-level-resource-maps/dni/New-Mexico-DNI-2017-01.jpg

However this map shows even the highest sunlight parts of New Mexico topping off at 6.1 kWh/sq-m per day, which is below a 20% capacity factor:
https://www.nrel.gov/gis/images/state-level-resource-maps/ghi/New-Mexico-ghi-2017-01.jpg

As I understand it both numbers are useful, with the first being more applicable to photovoltaic systems while the second is more applicable to solar concentration systems.  My layman's opinion is that photovoltaics are the future but that doesn't mean the other figure is wrong.  Plenty of smart money is getting put into concentration systems.  And broadly speaking, this is just quibbling over a few percentage points.  It is certainly not the case that an orbital system would only be twice the capacity factor of a system on the ground which was the original point.  To me a figure of 6 times as much seems pretty reasonable.

Online TrevorMonty

Re: Space Solar Power with BFR
« Reply #61 on: 05/04/2018 08:41 pm »



Added:
NOTE - For those worried about getting cooked the .23W/cm^2 is less than that produced by your cellphone of 1W/cm^2 next to your head.

Ok for growing crops but still wouldn't live in that area.

The biggest problem is finding 15km2 of un populated land near big city which would use the power. Off shore sites like current crop of wind farms might be better place to  build the ground station.

Offline rklaehn

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Re: Space Solar Power with BFR
« Reply #62 on: 05/04/2018 09:21 pm »
Northern Europe has about 30-50% of the world's demand for clean energy. Partly as a result, electricity is about double the price compared to the USA.
The world is growing, by the end of this century demand for energy is likely to be roughly proportional to population, making northern Europe niche.

True. But as long as the niche is big enough to justify a number of solar power satellites, what's the problem? >200GW for northern and central Europe is not exactly a tiny niche. Selling high performance electrical roadsters was also a niche, but nevertheless very useful for Tesla to get going.

In general, I think the notion that it is either space solar power or terrestrial solar power is wrong. Space solar power has some properties that are the exact opposite of ground solar power, so space solar power can initially only work to augment ground solar power.

Here is a plan for space solar power that might work. Space solar power works 24/7 and at night. It is independent of seasons, weather etc. A satellite can supply receivers on the entire hemisphere below it just by steering the beam.

Ground solar power is cheap, but there are large daily, weekly and seasonal fluctuations. These can be compensated to a degree by having a large scale power grids, but only to a degree.

Daily fluctuations: there will always be a time in the evening when there is high power demand but no solar power production.
Weekly fluctuations: if it is a dark and cloudy November all over Europe, even a large scale power grid won't help.
Seasonal fluctuations: Solar power production in Europe in winter will always be a factor of 3 or more less than in summer.

So let's design a space solar power satellite that is not designed for base load, but for wherever in the world there is the biggest mismatch between supply and demand. Such a system will be able to command much higher power prices, but it has to be designed in a completely different way.

Instead of designing for overall efficiency, such a system would be designed for minimal receiver costs, so you can afford to put receivers next to all regions with big power demand.

There is a startup called powerlight (ex lasermotive) that does infrared power transmission via lasers: http://powerlighttech.com/the-technology/ So the technology is not completely new. Receivers would be stratospheric platforms at an altitude of ~20km. Basically long cylindrical balloons covered in solar cells specially tuned for a single wavelength and optimised for low angle beams. The infrared wavelength could be chosen so that the lower atmosphere is opaque to it, completely eliminating the space based laser weapon fears.

The overall efficiency will be pretty bad (~50%), but power in space so cheap that it might not matter. Also, peak rates are way more than a factor of 2 higher than base rates.

So how would such a system work: You have receivers near many big power consumers. In the northern winter season, you first use the morning demand/supply mismatch in Japan, then China, India, Russia, Europe. After the sun has risen high enough in Europe to make ground solar power competitive, you steer the beam back to Japan to use the evening supply/demand mismatch, roughly following the terminator again. Occasionally you make a killing by supplying a region that has cloudy weather for an extended period, like e.g. Germany in foggy and windless November. In the southern winter, you basically do the same except that you more often supply the cities in the southern hemisphere (Australia, South Africa, South America). Of course you can still supply the northern hemisphere if there is higher demand. You just go wherever the price is highest.

Here you can see how high the daily fluctuations of power price are in germany: https://www.energy-charts.de/price.htm?year=2017&auction=1h&month=11

You can also see how ridiculously low the supply of solar and wind is for some weeks in december: https://www.energy-charts.de/price.htm?year=2017&auction=1h&month=12

Edit: here is what I mean by "making a killing":
https://www.energy-charts.de/price.htm?year=2017&auction=1h&week=4

Spot market prices for electricity went almost up to 200 EUR / MWh. That's 0.20 EUR/kWh.
« Last Edit: 05/04/2018 09:36 pm by rklaehn »

Offline speedevil

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Re: Space Solar Power with BFR
« Reply #63 on: 05/04/2018 10:11 pm »
At some point, the whole world should aim for European levels of power consumption.

I don't care if my fridge uses 80W or so average, or 8W, nor if my house similarly uses 10kW or 500W to maintain temperature.
I care about if it's cold/warm.

Power consumption is correlated with standard of living, but this is not simply causal.
If people would rather stay in and watch Star Wars on netflix (for example) than drive their car to the movie theater as they previously had to (in 1977), this is a significant net reduction in energy use, but not in any way an indicator of increased poverty.

Offline Robotbeat

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Re: Space Solar Power with BFR
« Reply #64 on: 05/05/2018 04:44 am »
I don't understand how you get to 10 times more in orbit than on the ground. The solar intensity at 1 AU is 1.36 kW. On the ground it is about 1 kW, depending on where you are, the weather, etc.

Because capacity factors for fixed solar on the ground are between about 0.1 (Germany, England) and 0.2 (Atacama desert).
...
Wrong. The American Southwest has statewide<[ capacity factors of about 26%. Parts of Chile are even higher.

Using Germany as an example is a red herring. It’s a terrible place for solar power. The vast majority of the world’s population and surface area gets vastly more sunlight.

A capacity factor of 26% would mean 8.1 kWh/sq-m per day by my math (1.3*24*.26).
This map shows that New Mexico is generally pretty close to that level but slightly shy:
https://www.nrel.gov/gis/images/state-level-resource-maps/dni/New-Mexico-DNI-2017-01.jpg
...
My statement is well-sourced. I do my research before quoting figures:
http://euanmearns.com/solar-pv-capacity-factors-in-the-us-the-eia-data/
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Offline Robotbeat

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Re: Space Solar Power with BFR
« Reply #65 on: 05/05/2018 04:45 am »
...
Latitude is not problem. It just means elongating the receiver a bit. ...
...by the same argument, just install more solar panels.
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Offline oldAtlas_Eguy

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Re: Space Solar Power with BFR
« Reply #66 on: 05/05/2018 05:53 pm »
It is a matter of economics. The rates the following document shows the actual comparison of various plat types and the costs of delivered power. Solar is marginally competitive with other conventional plant types. It is this competitive space that SSPS has to beat not just ground solar.https://www.eia.gov/outlooks/aeo/pdf/electricity_generation.pdf

Solar is estimated to be competitive in the future with conventional due to rising environmental costs for new and older fossil fuel plants. Again SSPS will be built if it can compete economically in this space.

Offline oldAtlas_Eguy

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Re: Space Solar Power with BFR
« Reply #67 on: 05/06/2018 07:06 pm »
Here is a economic model equation to determine if a SSPS will be competitive.

F - capacity factor increase of same weight in-orbit system over that of ground PV system at same location.

C - cost of ground PV system/kg (there is likely some trade offs here for in-orbit but the average costs is likely to be a he same or very close)

L - cost of launch $/kg

(L+ C)/F <= C

If this is true then SSPS is competitive.

Added:
Or put another way.
L<=(F-1)*C
Example:
If C is $10/kg
And F is 5
Then L would have to be <= to $40/kg for an SSPS to be competitive.
« Last Edit: 05/06/2018 07:22 pm by oldAtlas_Eguy »

Offline johnfwhitesell

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Re: Space Solar Power with BFR
« Reply #68 on: 05/06/2018 07:52 pm »
It is a matter of economics. The rates the following document shows the actual comparison of various plat types and the costs of delivered power. Solar is marginally competitive with other conventional plant types. It is this competitive space that SSPS has to beat not just ground solar.https://www.eia.gov/outlooks/aeo/pdf/electricity_generation.pdf

Solar is estimated to be competitive in the future with conventional due to rising environmental costs for new and older fossil fuel plants. Again SSPS will be built if it can compete economically in this space.

EIA numbers are consistently inaccurate about solar, overestimating the costs.  Generally this is restricted to the future but sometimes it even extends into the present.  For example:

Understated forecasts are driven by overestimated costs. For example, the EIA recently estimated solar would cost $2,480 per kW in 2017. In fact, the Solar Energy Industries Association (SEIA) reports utility solar costs had already fallen to around $1,200/kilowatt (kW) last year.

Now if it was just a matter of differing measurements that would be one thing but there is a very large market for utility solar electricity supplies and those contracts are typically publicly disclosed because they are with government customers.

So if you look at an EIA report and think solar is one of the things to beat you should adjust for the EIA's consistent error and instead conclude that solar is the thing to beat.
« Last Edit: 05/06/2018 07:53 pm by johnfwhitesell »

Offline niwax

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Re: Space Solar Power with BFR
« Reply #69 on: 05/06/2018 08:00 pm »
...
Latitude is not problem. It just means elongating the receiver a bit. ...
...by the same argument, just install more solar panels.

Is either necessary for northern Europe? They're doing just fine with hydro and are perfectly positioned for offshore wind + tidal.
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Offline oldAtlas_Eguy

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Re: Space Solar Power with BFR
« Reply #70 on: 05/06/2018 09:02 pm »
The economic trades-pace shows that if BFR reaches it goal of $13/kg it would produce power the lowest cost electricity even if the F=3 and C=$5/kg. The entry into the competitive space has a likely point of around $100/kg for L. This due to the competitive generation tradespace from best to worst for ground systems vary by > a factor of 2.
« Last Edit: 05/06/2018 09:03 pm by oldAtlas_Eguy »

Offline Exastro

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Re: Space Solar Power with BFR
« Reply #71 on: 05/06/2018 09:05 pm »
...
Latitude is not problem. It just means elongating the receiver a bit. ...
...by the same argument, just install more solar panels.

Are you sure that's fair?  I haven't thought through the physics carefully, but my gut says the elements of a tilted rectenna would need to be spaced further apart to accommodate the off-perpendicular beam, but that no more rectennas would be needed.  This is in contrast to solar panels placed flat on the ground, whose total area would need to increase to let them cover the same projected area as seen from the Sun.  But it's  analogous to solar panels which can be individually tilted to face the Sun (but which would then have to be spread out to avoid shadowing each other).

Kinda subtle.

Offline Robotbeat

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Re: Space Solar Power with BFR
« Reply #72 on: 05/06/2018 11:59 pm »
...
Latitude is not problem. It just means elongating the receiver a bit. ...
...by the same argument, just install more solar panels.

Are you sure that's fair?  I haven't thought through the physics carefully, but my gut says the elements of a tilted rectenna would need to be spaced further apart to accommodate the off-perpendicular beam, but that no more rectennas would be needed.  This is in contrast to solar panels placed flat on the ground, whose total area would need to increase to let them cover the same projected area as seen from the Sun.  But it's  analogous to solar panels which can be individually tilted to face the Sun (but which would then have to be spread out to avoid shadowing each other).

Kinda subtle.
In both case you can tilt them to have about the same collection, just spread out. Solar is beamed fusion from the Sun, and the photovoltaic array is merely the receiver.
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Offline Exastro

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Re: Space Solar Power with BFR
« Reply #73 on: 05/07/2018 01:12 am »
...
Latitude is not problem. It just means elongating the receiver a bit. ...
...by the same argument, just install more solar panels.

Are you sure that's fair?  I haven't thought through the physics carefully, but my gut says the elements of a tilted rectenna would need to be spaced further apart to accommodate the off-perpendicular beam, but that no more rectennas would be needed.  This is in contrast to solar panels placed flat on the ground, whose total area would need to increase to let them cover the same projected area as seen from the Sun.  But it's  analogous to solar panels which can be individually tilted to face the Sun (but which would then have to be spread out to avoid shadowing each other).

Kinda subtle.
In both case you can tilt them to have about the same collection, just spread out. Solar is beamed fusion from the Sun, and the photovoltaic array is merely the receiver.
So the difference (as I understand it) is that the rectenna elements don't have to be tilted, just spread further apart.  That should reduce the cost of accommodating a non-perpendicular beam relative to solar panels. 

Offline Robotbeat

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Re: Space Solar Power with BFR
« Reply #74 on: 05/07/2018 01:56 am »
I’m not sure that’s quite true. Anyway, the other thing with solar at high latitudes is the seasonal variation. Not a problem for space solar.
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Offline alexterrell

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Re: Space Solar Power with BFR
« Reply #75 on: 05/07/2018 08:00 am »
Here is a economic model equation to determine if a SSPS will be competitive.

F - capacity factor increase of same weight in-orbit system over that of ground PV system at same location.

C - cost of ground PV system/kg (there is likely some trade offs here for in-orbit but the average costs is likely to be a he same or very close)

L - cost of launch $/kg

(L+ C)/F <= C

If this is true then SSPS is competitive.

Added:
Or put another way.
L<=(F-1)*C
Example:
If C is $10/kg
And F is 5
Then L would have to be <= to $40/kg for an SSPS to be competitive.

This ignores the cost of intermitency.

You can use your model to account for this. In Germany, in December, the capacity factor of solar power is about 3%.

The in space solution will deliver 99% x ~1.3 (no atmosphere) x ~0.5 (transmission losses), so F = 20.

But this makes the point: For northern latitudes, the competition is not ground solar, because solar cannot deliver base load power, without some break through in storage.

For the UK, the competition is nuclear power, mixed with wind. That is an expensive mix.

For Germany, the competition is basically nuclear fusion - without a really good wind resource, and having eschewed nuclear fission, Germany has no viable route to decarbonising. This is the situation of the Energiewende:
https://pmpaspeakingofprecision.files.wordpress.com/2015/03/then-a-miracle-occurs-logic-1050x700.jpg

Either way, massively reduced launch costs and system masses work in favour of SPS:

8GW of space solar power, delivering 4GW to the grid, costs: $8 billion
Launch cost: Assume 10,000 tons at $100/kg: $1 billion

Total, $9 billion.
For the UK, compared to 4GW of nuclear, total $20 billion (or $32 billion at Hinkley C costs).
For Germany, compared to an as yet unknown solution.

The launch cost is pretty trivial. Even at $1000/kg, the installation price is similar to nuclear. (Nuclear will have higher operating costs, but a life time of 60 to 80 years).

Countries at lower latitudes have more options for solar. California could go renewable with a mere 20TWh of storage.
http://euanmearns.com/how-californias-electricity-sector-can-go-100-renewable/
Once this is costed, then we can assume F = 5, as above.

Offline alexterrell

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Re: Space Solar Power with BFR
« Reply #76 on: 05/07/2018 08:08 am »

So the difference (as I understand it) is that the rectenna elements don't have to be tilted, just spread further apart.  That should reduce the cost of accommodating a non-perpendicular beam relative to solar panels. 
That is one difference.

However, the bigger difference is that a solar farm typically occupies all the land it's built on. The PR tells you it can be used to shelter sheep, but all the ones I see round here have cut grass around them.

A rectenna is a much lighter structure, that could be mounted over crops. Or assembled over shallow waters like the Thames Estuary, or a floating platform in the Bay off Vancouver.

Offline alexterrell

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Re: Space Solar Power with BFR
« Reply #77 on: 05/07/2018 08:21 am »
One of the most believable current proposals for bringing solar energy on a large scale to Europe is by connecting mega-grids to the MENAT (Middle East, North Africa, and Turkey) region, where huge amounts of investment and technology development are going into solar farms. Given that this is the current direction that green energy in Europe is likely to take, the question for the BFR providing us with space solar power, is can it make SSP cheaper than connecting our grids across to Morocco and Arabia?
It's not really competing with large scale solar power on the ground in Europe, as at that point it's better to use large solar farms further South than to build them in our rainy lands.

Actually it's a former proposal - http://www.desertec.org/. (It is still just about alive, but slimmed down).

It is still believable, but the key would be to wait until these countries are 100% off fossil fuels, and then they can start to export their surplus.

The main issues are that
1. HVDC costs about €1 billion per 1000km per GW.
2. Many of these countries are politically unstable. Europe has enough worries over gas from unfriendly neighbours, without adding electricity to the mix. Saudi Arabia would be nice - generating power for European breakfast time - but the HVDC cable would have to pass through Syria or Israel.
3. The Sahara is still slightly seasonal, but Europe needs more electricity in winter.
4. The original proposal was to use Solar Thermal Power, with night time thermal storage. Since then, PV prices have fallen much faster than solar thermal prices - but there is still the overnight storage issue.

Offline Slarty1080

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Re: Space Solar Power with BFR
« Reply #78 on: 05/07/2018 12:01 pm »
The BFR has its own solar arrays for use in space. Could these be utilized on the surface of Mars? Or would they just collapse under gravity? Given the premium on cargo weight it would seem sensible to make full use of these panels if at all possible.
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Offline speedevil

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Re: Space Solar Power with BFR
« Reply #79 on: 05/08/2018 10:37 am »
The BFR has its own solar arrays for use in space. Could these be utilized on the surface of Mars? Or would they just collapse under gravity? Given the premium on cargo weight it would seem sensible to make full use of these panels if at all possible.
In principle, the arrays shown can be used on the surface, if they can either support their weight directly, or with the use of additional guy wires.
As one sketch, if we assume there is a lifting hook fixture of some form at the top of the vehicle (perhaps not at the nose) , simply stringing an equilateral triangle of wire from that down to two anchor points on the ground, and adding two attach points for the inboard sides of the panels may let the panels lie in front of the wings in a usable attitude.
It may make more sense to detach them.
It is unclear if the solar panel design is more than notional.

The panels shown are about 12m in radius, covering around two thirds of a circle, or 70m^2.
At 25% efficiency, they produce around 20kW near earth.
Landed on Mars, they produce around half a percent of the power needed for ISRU - it's not worth optimising very much for reusing them, though they could obviously be useful for short-term power.

Offline LMT

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Re: Space Solar Power with BFR
« Reply #80 on: 05/16/2018 05:32 pm »
The BFR has its own solar arrays for use in space. Could these be utilized on the surface of Mars? Or would they just collapse under gravity? Given the premium on cargo weight it would seem sensible to make full use of these panels if at all possible.
In principle, the arrays shown can be used on the surface, if they can either support their weight directly, or with the use of additional guy wires.
As one sketch, if we assume there is a lifting hook fixture of some form at the top of the vehicle (perhaps not at the nose) , simply stringing an equilateral triangle of wire from that down to two anchor points on the ground, and adding two attach points for the inboard sides of the panels may let the panels lie in front of the wings in a usable attitude.
It may make more sense to detach them.
It is unclear if the solar panel design is more than notional.

The panels shown are about 12m in radius, covering around two thirds of a circle, or 70m^2.
At 25% efficiency, they produce around 20kW near earth.
Landed on Mars, they produce around half a percent of the power needed for ISRU - it's not worth optimising very much for reusing them, though they could obviously be useful for short-term power.

Perhaps ITS onboard solar arrays are no longer needed on the martian surface, as of 2018.  Quantum dot solar cells presently have an exceptional rating of 15.2 kW/kg.  While too fragile for use as ITS solar arrays, they could serve well on the martian surface, e.g., for scaled ISRU.



One ITS payload of quantum dot PV panels could provide max power of ~ 1 GW on Mars.

What do you think?  Now that we're measuring martian PV performance in terms of "GW per payload", have we moved beyond the concern with ITS onboard solar array performance on Mars?

--

Dust devils would pose a real threat to these fragile quantum dot PV panels.  How to protect?  You could always add protective layers of course.  But perhaps "canopy deployment" would provide sufficient protection itself, without addition of more layers.  If panels were deployed overhead, using some tent-pole system, the panels would be positioned above the altitude of the dust devil's abrasive sand saltation region (<1 m altitude).  Only fine dust would impact the panels. 

Conceptually:



Practical energy storage remains a challenge, of course.  How to store the midday peak PV terajoules through the night, or through dim winter months?
« Last Edit: 05/16/2018 05:43 pm by LMT »

Offline oldAtlas_Eguy

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Re: Space Solar Power with BFR
« Reply #81 on: 05/16/2018 06:24 pm »
The BFR has its own solar arrays for use in space. Could these be utilized on the surface of Mars? Or would they just collapse under gravity? Given the premium on cargo weight it would seem sensible to make full use of these panels if at all possible.
In principle, the arrays shown can be used on the surface, if they can either support their weight directly, or with the use of additional guy wires.
As one sketch, if we assume there is a lifting hook fixture of some form at the top of the vehicle (perhaps not at the nose) , simply stringing an equilateral triangle of wire from that down to two anchor points on the ground, and adding two attach points for the inboard sides of the panels may let the panels lie in front of the wings in a usable attitude.
It may make more sense to detach them.
It is unclear if the solar panel design is more than notional.

The panels shown are about 12m in radius, covering around two thirds of a circle, or 70m^2.
At 25% efficiency, they produce around 20kW near earth.
Landed on Mars, they produce around half a percent of the power needed for ISRU - it's not worth optimising very much for reusing them, though they could obviously be useful for short-term power.

Perhaps ITS onboard solar arrays are no longer needed on the martian surface, as of 2018.  Quantum dot solar cells presently have an exceptional rating of 15.2 kW/kg.  While too fragile for use as ITS solar arrays, they could serve well on the martian surface, e.g., for scaled ISRU.



One ITS payload of quantum dot PV panels could provide max power of ~ 1 GW on Mars.

What do you think?  Now that we're measuring martian PV performance in terms of "GW per payload", have we moved beyond the concern with ITS onboard solar array performance on Mars?

--

Dust devils would pose a real threat to these fragile quantum dot PV panels.  How to protect?  You could always add protective layers of course.  But perhaps "canopy deployment" would provide sufficient protection itself, without addition of more layers.  If panels were deployed overhead, using some tent-pole system, the panels would be positioned above the altitude of the dust devil's abrasive sand saltation region (<1 m altitude).  Only fine dust would impact the panels. 

Conceptually:



Practical energy storage remains a challenge, of course.  How to store the midday peak PV terajoules through the night, or through dim winter months?
A full 150mt payload with a system using such cells considering you are on Mars not Earth, structures, wiring/cables, and power conditioning with batteries the continuous output would be ~ 60MW.

Since this is a discussion on SPS around Earth. For every 5 BFR loads you could generate and beam to Earth 1GW.
1 BFR solar cells
1 BFR solar cells structures
2 BFR power transmission antenna
1 BFR of propellant for electric thrusters to move sat to GEO

At even only a 50% transmission and delivery to the electric grid efficiency that is a requirement of 50 BFR launches to be able to deliver 5GW continuous power on Earth.
« Last Edit: 05/16/2018 06:41 pm by oldAtlas_Eguy »

Offline speedevil

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Re: Space Solar Power with BFR
« Reply #82 on: 05/16/2018 06:59 pm »
Perhaps ITS onboard solar arrays are no longer needed on the martian surface, as of 2018.  Quantum dot solar cells presently have an exceptional rating of 15.2 kW/kg.  While too fragile for use as ITS solar arrays, they could serve well on the martian surface, e.g., for scaled ISRU.

These are far, far, far too fragile for use on the Martian surface, without considerable post-processing into panels using native resources - cover glass and encapsulant at least.
Quote
Herein, we report an extremely lightweight and ultra-flexible CQD solar cell constructed on a polyethylene naphthalate substrate with a thickness of 1.3 μm.
1.3um thick plastic film is _ridiculously_ fragile.

Offline LMT

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Re: Space Solar Power with BFR
« Reply #83 on: 05/16/2018 07:35 pm »
A full 150mt payload with a system using such cells considering you are on Mars not Earth, structures, wiring/cables, and power conditioning with batteries the continuous output would be ~ 60MW.

Oh, the only real structure would be the "tent-poles", which I suppose you might fabricate from regolith, via laser additive mfg.  Much else is just conductive tension wiring, maybe coated carbon.  And that couldn't mass much.  So ~ 1 GW max, yes.

As for batteries and other "continuous output" hardware, those are separate systems.  Again, storage of the terajoules is a challenge, perhaps a daunting one. 

Offline LMT

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Re: Space Solar Power with BFR
« Reply #84 on: 05/16/2018 07:49 pm »
Perhaps ITS onboard solar arrays are no longer needed on the martian surface, as of 2018.  Quantum dot solar cells presently have an exceptional rating of 15.2 kW/kg.  While too fragile for use as ITS solar arrays, they could serve well on the martian surface, e.g., for scaled ISRU.

These are far, far, far too fragile for use on the Martian surface

?  Polyethylene naphthalate is a high-performance material:  a common IC substrate, a tough fiber.  The solar cells are reported having "durable mechanical properties" suitable for use on satellites, for example.  Probably not suitable for the rigors of ITS adventures, but ok in space, generally.

As for Mars, if you eliminate the sand saltation problem by elevating the panels, what's the remaining hazard that renders the panels "far, far, far too fragile" to just... sit there?

Offline speedevil

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Re: Space Solar Power with BFR
« Reply #85 on: 05/16/2018 08:04 pm »
?  Polyethylene naphthalate is a high-performance material:  a common IC substrate, a tough fiber.  The solar cells are reported having "durable mechanical properties" suitable for use on satellites, for example.  Probably not suitable for the rigors of ITS adventures, but ok in space, generally.

As for Mars, if you eliminate the sand saltation problem by elevating the panels, what's the remaining hazard that renders the panels "far, far, far too fragile" to just... sit there?

Its properties are broadly similar to PET, but this is less relevant when it is so thin. 1.3um is ten times thinner than common cling-film, ten times thinner than the thinnest human hair.

The windloads from martian winds may be approximately equal to 10m/s or so on earth, in storms, but even in more modest winds, this can excite flapping, which will destroy the film, as you can't guy it tight enough.


Offline LMT

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Re: Space Solar Power with BFR
« Reply #86 on: 05/16/2018 09:50 pm »
The windloads from martian winds may be approximately equal to 10m/s or so on earth, in storms, but even in more modest winds, this can excite flapping, which will destroy the film, as you can't guy it tight enough.

The tensile yield strength is much higher than that of typical "plastic".  As for guy-wires, this is just a tensile membrane structure:  you can always grid a few thin wires across the fabric surfaces, as tightly as needed, to distribute storm load and prevent flapping.  This is common in tensile membrane structures.  And given the tiny storm forces, not an issue.

Offline alexterrell

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Re: Space Solar Power with BFR
« Reply #87 on: 06/04/2018 09:24 am »
Perhaps ITS onboard solar arrays are no longer needed on the martian surface, as of 2018.  Quantum dot solar cells presently have an exceptional rating of 15.2 kW/kg.  While too fragile for use as ITS solar arrays, they could serve well on the martian surface, e.g., for scaled ISRU.



My original premise was that the economic challenges of Space Solar Power could be overcome by:
1. Falling launch costs with BFR
2. Falling mass requirements thanks to better solar cells and better structures.

15KW/kg is ridiculously light. That is only about 500 tons of cells for an 8GW system, delivering 4GW to Earth.

The lighter the cells, the lighter the supporting structures need to be - at least till dealing with solar wind becomes an issue. We're probably still talking 5,000 to 10,000 tons for mass to orbit, which, with BFR, is quite affordable.

Back on Earth, the 15KW/kg makes little difference. It still needs to be protected from hail and sand and pigeon muck, and the water jet used to clean the muck.

Offline LMT

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Re: Space Solar Power with BFR
« Reply #88 on: 06/04/2018 11:25 pm »
Perhaps ITS onboard solar arrays are no longer needed on the martian surface, as of 2018.  Quantum dot solar cells presently have an exceptional rating of 15.2 kW/kg.  While too fragile for use as ITS solar arrays, they could serve well on the martian surface, e.g., for scaled ISRU.



My original premise was that the economic challenges of Space Solar Power could be overcome by:
1. Falling launch costs with BFR
2. Falling mass requirements thanks to better solar cells and better structures.

15KW/kg is ridiculously light. That is only about 500 tons of cells for an 8GW system, delivering 4GW to Earth.

The lighter the cells, the lighter the supporting structures need to be - at least till dealing with solar wind becomes an issue. We're probably still talking 5,000 to 10,000 tons for mass to orbit, which, with BFR, is quite affordable.

One way of looking at it:  These ultra-mass-efficient solar cells give you excess electrical power for robust ISEP. And ISEP allows your Space Solar Power structure to orbit below all commercial sats, at 250 km or less.  From that vantage you have an unobstructed shot at your rectennae, at the minimum possible range, with maximum possible transmission efficiency. 

Moreover, you could minimize SSP mass by piggybacking SSP onto the Terrestation structure.  The extra SSP panels would unfurl like the notional trawler panels, as "petals" on the base rim, rolling out under roughly martian g.  The panels would require negligible additional structural mass.  Centripetal acceleration would stabilize the panels against solar wind, photon pressure and atmospheric drag; but you might need to design SSP panel circuits for high voltage / low current, or use symmetric current loops, to prevent distortion under interaction with the geomagnetic field.

The only big SSP mass would be the conversion & transmission system, yes?  It might be mounted most efficiently as a "sandwich module" layer (Jaffe et al. 2011) affixed beneath each solar cell, as for example in the thermally-optimized module design of Yang et al. 2017. 



If continuous SSP daytime power transmission were required in a given region, multiple rectennae could be deployed across the extent of the regional power grid, and a cluster of small-scale Terrestation SSPs could be deployed.  Regional rectennae could capture power continuously from a subset of SSPs, with distribution through the network.

How would those changes improve your SSP cargo mass estimate?  Very significantly, I'd think.

Refs

Jaffe, P., Pasour, J., Gonzalez, M., Spencer, S., Nurnberger, M., Dunay, J., ... & Jenkins, P. (2011, March). Sandwich module development for space solar power. In Proceedings of the 28th International Symposium on Space Technology and Science.

Yang, C., Hou, X., & Wang, L. (2017). Thermal design, analysis and comparison on three concepts of space solar power satellite. Acta Astronautica, 137, 382-402.
« Last Edit: 12/03/2020 03:36 am by LMT »

Offline guckyfan

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Re: Space Solar Power with BFR
« Reply #89 on: 06/05/2018 06:42 am »
If you put the solar arrays that low you lose the one big advantage that space solar has over ground based solar. It is shaded during the night.

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Re: Space Solar Power with BFR
« Reply #90 on: 06/05/2018 11:32 am »
If you put the solar arrays that low you lose the one big advantage that space solar has over ground based solar. It is shaded during the night.
Which is an even bigger problem - still - in northern latitude winters.

Since it seems the power density of the Earth based rectenna is limiting factor, I'm not sure being so close to Earth is a major advantage at large scale.

Offline Robotbeat

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Re: Space Solar Power with BFR
« Reply #91 on: 06/05/2018 12:46 pm »
If you put the solar arrays that low you lose the one big advantage that space solar has over ground based solar. It is shaded during the night.
Which is an even bigger problem - still - in northern latitude winters.

Since it seems the power density of the Earth based rectenna is limiting factor, I'm not sure being so close to Earth is a major advantage at large scale.
Im a fan of removing those limits and just making it a no-fly zone.
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Offline LMT

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Re: Space Solar Power with BFR
« Reply #92 on: 06/05/2018 02:35 pm »
If you put the solar arrays that low you lose the one big advantage that space solar has over ground based solar. It is shaded during the night.

No, there are many LEO SSP designs.

Comparing e.g. geosync to 250 km: 

@250 cuts the SSP mass by ~ 10,000x, per the inverse r^2 law of EM propagation, and night shutdown.

Consequence:  There is no terrestrial business case for geosync SSP. 

Offline guckyfan

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Re: Space Solar Power with BFR
« Reply #93 on: 06/05/2018 02:47 pm »
If you put the solar arrays that low you lose the one big advantage that space solar has over ground based solar. It is shaded during the night.

No, there are many LEO SSP designs.

That does not make it any better. Those sats still can only serve the area during the day. If space solar has any advantage, it is providing power during the night.

Edit: Also it does not change that these sats would be in shadow half of the time, cutting their productivity by half.
« Last Edit: 06/05/2018 02:48 pm by guckyfan »

Offline LMT

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Re: Space Solar Power with BFR
« Reply #94 on: 06/05/2018 07:16 pm »
these sats would be in shadow half of the time, cutting their productivity by half.

Hence the 10,000x mass cut.  It's factored in.

10,000x less mass -- that's a lot less, isn't it?

But which LEO SSP design do you find most promising, and why? 

--

It would be interesting to compare the previous best LEO SSP $/kW against piggybacked Terrestation SSP, apples-to-apples.  I suspect Terrestation SSP would beat the previous best, easily, for reasons above.  And of course geosync SSP couldn't compete.

If space solar has any advantage, it is providing power during the night.

We shouldn't grossly oversimplify.  For example, regional power grids would route SSP to cities, day and night; though of course cities pull less power at night.  Plus the emerging global power grid would route SSP worldwide.  Power distribution grids must be remembered in trade-off analysis.



Offline LMT

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Re: Space Solar Power with BFR
« Reply #95 on: 06/06/2018 01:33 am »
Since it seems the power density of the Earth based rectenna is limiting factor, I'm not sure being so close to Earth is a major advantage at large scale.

?

You understand that for any given rectenna, a 250-km orbit cuts the matching SSP system mass by ~ 10,000x, relative to geosync SSP mass, yes?

Example:

A rectenna set is matched with a single-launch, 150-ton SSP system that's piggybacked on the Terrestation @250.

The equivalent geosync SSP hardware would mass 1,500,000 tons, plus all additional structure, for a total of perhaps 3,000,000 tons.

SSP cargo mass saved @250 Terrestation:  2,999,850 tons.

A major advantage.
« Last Edit: 06/06/2018 02:17 am by LMT »

Offline LMT

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Re: Space Solar Power with BFR
« Reply #96 on: 06/06/2018 01:59 am »
Back on Earth, the [quantum dot panel's] 15KW/kg makes little difference. It still needs to be protected from hail and sand and pigeon muck, and the water jet used to clean the muck.

Mars lacks pigeons and hail, and lacks sand above 1 m altitude.

Also dust devils clean solar panels rather well, as below.

So do you think a multi-GW quantum dot PV farm is practicable on Mars?


Offline alexterrell

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Re: Space Solar Power with BFR
« Reply #97 on: 06/06/2018 07:36 am »
Since it seems the power density of the Earth based rectenna is limiting factor, I'm not sure being so close to Earth is a major advantage at large scale.

?

You understand that for any given rectenna, a 250-km orbit cuts the matching SSP system mass by ~ 10,000x, relative to geosync SSP mass, yes?

Example:

A rectenna set is matched with a single-launch, 150-ton SSP system that's piggybacked on the Terrestation @250.

The equivalent geosync SSP hardware would mass 1,500,000 tons, plus all additional structure, for a total of perhaps 3,000,000 tons.

SSP cargo mass saved @250 Terrestation:  2,999,850 tons.

A major advantage.

No, it cuts the rectenna mass by about 10,000 times. However, it more than doubles the required solar power systems mass and associated support mass, and also introduces lots of questions of station keeping (flying a parachute in the Thermoshpere.

Low Earth Orbit systems have been proposed for early stage development, in the MW scale, where a GEO scale rectenna would not be feasible.

But once you get to GW scale, GEO makes sense. If we have 5,000 tons of rectenna and 5,000 of other system in GEO (10,000 tons), I can now replace it with 0.5 tons of rectenna and 10,000 tons other systems (still 10,000 tons).

And my LEO system still suffers from seasonal effects, still needs significant propulsive manouvering to remain in LEO, still needs a whole network of ground stations to switch to, and still only works during the day time. So all the disadvantages of Earth based solar.

This of course highlights what has been a major problem with GEO SSP - it only really works at the >GW scale. In the 1970s studies, this was about 100,000 tons delivering 5GW. Hence the suggestions of LEO prototypes. Now it's about 10,000 tons delivering 5GW - which with BFR may become feasible.

Offline alexterrell

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Re: Space Solar Power with BFR
« Reply #98 on: 06/06/2018 07:44 am »
If you put the solar arrays that low you lose the one big advantage that space solar has over ground based solar. It is shaded during the night.
Which is an even bigger problem - still - in northern latitude winters.

Since it seems the power density of the Earth based rectenna is limiting factor, I'm not sure being so close to Earth is a major advantage at large scale.
Im a fan of removing those limits and just making it a no-fly zone.

If these limits are human and biological, then certainly raise them. Something of the order of 1-2 KW/m2 is very useful, but still not powerful enough to be used as a weapon. (Cue Sci fi plot - bad guy takes over a dozen Powersats simultaneously, and directs them all at his target - where upon, with hero chained up, the beams interfere with each other and have no effect)

However - from sbove:

Attached is a NASA study titled "Satellite Power Systems (SPS) Concept Definition Study" done by Rockwell in 1980.

Page 14 states "power output must be decreased to satisfy the 23 mW/cm2 (0.23 kW/m2) RF energy constraint in the atmosphere to avoid potential microwave interference with the D and F layers of the atmosphere." Seems to be an issue with microwave power transmission through the ionosphere.

Does that mean .23 kW/m2 is a physical limit? What do they mean by "potential" interference, and what are the consequences?

Of course, if the Earth based rectenna has to be quadrupled in area, it means that the powersat antenna can be quartered in area.

Offline alexterrell

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Re: Space Solar Power with BFR
« Reply #99 on: 06/06/2018 07:50 am »

So do you think a multi-GW quantum dot PV farm is practicable on Mars?

Try and lay out 50 square kilometres of cling film in the Atacama desert, and then we can assess whether this can be done on Mars.

You will end up building a glass factory and sandwiching the cells between sheets of glass.
« Last Edit: 06/06/2018 07:52 am by alexterrell »

Offline LMT

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Re: Space Solar Power with BFR
« Reply #100 on: 06/06/2018 11:27 am »

So do you think a multi-GW quantum dot PV farm is practicable on Mars?

Try and lay out 50 square kilometres of cling film in the Atacama desert, and then we can assess whether this can be done on Mars.

You will end up building a glass factory and sandwiching the cells between sheets of glass.

?  Why would you want a glass factory for martian panel deployment as below?  Quantum dot solar cells were designed for use in space without glass or other high-mass layers, intentionally.

« Last Edit: 06/06/2018 04:50 pm by LMT »

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Re: Space Solar Power with BFR
« Reply #101 on: 06/06/2018 12:42 pm »
No, it cuts the rectenna mass by about 10,000 times.

Here rectenna mass is fixed, hence "given".  I was comparing the required SSP orbiting mass at the two distances, for a given rectenna's given power output.  Focus first on that specific comparison.  It's "the money", to first approximation.

lots of questions of station keeping (flying a parachute in the Thermoshpere)

I introduced ISEP into forum, in another thread.  If you see big issues in the ISEP literature, or in the particular application, note them.  OT here.

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Re: Space Solar Power with BFR
« Reply #102 on: 06/06/2018 04:22 pm »
What are presently the best candidate SSP rectenna designs?

Presumably the best designs operate at 5.8 GHz, due to that frequency's high ionosphere constraint.

The 5.8 GHz rectenna of Ahn & Oh 2018 is rated with gain of 10.1 dBi and conversion efficiency of 75%.

What are some other great designs?

Refs

Ahn, C. H., & Oh, S. (2018). High gain pentagonal loop rectifying antenna. Microwave and Optical Technology Letters, 60(5), 1075-1079.
« Last Edit: 06/07/2018 11:12 pm by LMT »

Offline oldAtlas_Eguy

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Re: Space Solar Power with BFR
« Reply #103 on: 06/06/2018 05:49 pm »
No, it cuts the rectenna mass by about 10,000 times.

Here rectenna mass is fixed, hence "given".  I was comparing the required SSP orbiting mass at the two distances, for a given rectenna's given power output.  Focus first on that specific comparison.  It's "the money", to first approximation.

lots of questions of station keeping (flying a parachute in the Thermoshpere)

I introduced ISEP into forum, in another thread.  If you see big issues in the ISEP literature, or in the particular application, note them.  OT here.
It is called antenna gain.
The difference in efficiencies of a Leo to geo system is that the rectenna output is 80% of SSP input transmitter power and the geo is 50%. That is only a difference factor at best 1.6X for same weight SSP and same size rectenna. But the Leo system suffers from off angle losses making it generally less efficient in the long run. Remember the transmitter antennas are phased arrays of greater than 1km in size. This creates beam widths in significantly less than 1 degree. Transmission loss is totally dependent on beam forming and edges/lobes. With such large sizes this makes only small difference between Leo and geo.

The only real mass advantage is that with propulsion to put the mass from Leo  into geo. It with massive amounts of electrical power available use of some form of electrical propulsion with > 1000ISP the disadvantage is only a fraction of the SSP mass.
« Last Edit: 06/06/2018 05:52 pm by oldAtlas_Eguy »

Offline LMT

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Re: Space Solar Power with BFR
« Reply #104 on: 06/07/2018 01:46 am »
The difference in efficiencies of a Leo to geo system is that the rectenna output is 80% of SSP input transmitter power and the geo is 50%...  Remember the transmitter antennas are phased arrays of greater than 1km in size.

Terrestation transmitter diameter is 1.6 km+, giving a beam tighter than that of your 1 km transmitter.

Also, again, received power density follows 1/r^2.

So your LEO 30% increase in rectenna power output can't be correct, and is very far off.
« Last Edit: 06/07/2018 01:47 am by LMT »

Offline alexterrell

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Re: Space Solar Power with BFR
« Reply #105 on: 06/08/2018 05:09 pm »

So do you think a multi-GW quantum dot PV farm is practicable on Mars?

Try and lay out 50 square kilometres of cling film in the Atacama desert, and then we can assess whether this can be done on Mars.

You will end up building a glass factory and sandwiching the cells between sheets of glass.

?  Why would you want a glass factory for martian panel deployment as below?  Quantum dot solar cells were designed for use in space without glass or other high-mass layers, intentionally.

Designed for space. Mars surface is not the same as space. Whilst it's not as presented in "The Martian" you will still not be able to place materials as thin as a quantum dot array. Even deployment will probably be impossible.

Offline guckyfan

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Re: Space Solar Power with BFR
« Reply #106 on: 06/08/2018 06:28 pm »
Designed for space. Mars surface is not the same as space. Whilst it's not as presented in "The Martian" you will still not be able to place materials as thin as a quantum dot array. Even deployment will probably be impossible.

Maybe it needs to be laminated on a 50 micrometer mylar sheet.

Offline LMT

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Re: Space Solar Power with BFR
« Reply #107 on: 06/08/2018 06:46 pm »
?  Why would you want a glass factory for martian panel deployment as below?  Quantum dot solar cells were designed for use in space without glass or other high-mass layers, intentionally.
Designed for space. Mars surface is not the same as space. Whilst it's not as presented in "The Martian" you will still not be able to place materials as thin as a quantum dot array. Even deployment will probably be impossible.

Unrolling a PV panel and tensioning it, impossible?  The assertion needs a reason, maybe a fact or two.  QD solar cells have good mechanical properties by design.




Offline alexterrell

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Re: Space Solar Power with BFR
« Reply #108 on: 06/10/2018 09:01 am »
That photo is 1% QD solar panels and 99% tough, durable, plastic. It even has rigidity (try holding cling film like that - and then imagine it's about 8 times thinner).

Of course you can deploy it like that - with the sensitive bits wrapped up and tear proof. You might also consider Gorilla Glass - either will be suitable for the structures on Mars. Perhaps aluminium foil backing and plastic over coating?

But the only place you'll get 15.2KW/kg is in vacuum and in zero-g (or in a lab). And if you want to go to significant sizes (kms across), then that probably rules out LEO as well.

Even there, deployment might be an issue. If it holds a charge, it will hold electrostatic forces and be tricky - but not impossible - to unreel.

Offline LMT

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Re: Space Solar Power with BFR
« Reply #109 on: 06/10/2018 01:29 pm »
Maybe it needs to be laminated on a 50 micrometer mylar sheet.

You might also consider Gorilla Glass...

Perhaps aluminium foil backing and plastic over coating?

So as you see, QD solar cells don't require glass, Gorilla or other.  Multiple industrial examples make that clear enough.

As for aluminum foil, "plastic over coating", Mylar and the like...  the record-setting QD solar cells were produced on PEN because it's mechanically better than those other materials.  Hence the record, hooray.  You're petitioning for materials with lower tensile strength.   ::)
« Last Edit: 06/13/2018 03:03 am by LMT »

Offline speedevil

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Re: Space Solar Power with BFR
« Reply #110 on: 06/10/2018 01:30 pm »
As for aluminum foil, "plastic over coating", Mylar and the like...  the record-setting QD solar cells were produced on PEN because it's mechanically better than those other films.  Hence the record, hooray.  You're petitioning for materials with lower tensile strength.   ::)

It is not one hundred times better.
Thickness matters.
Plus, you can't strain it anywhere close to its yield without damaging the cells adhered to it.

Offline LMT

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Re: Space Solar Power with BFR
« Reply #111 on: 06/10/2018 01:38 pm »
As for aluminum foil, "plastic over coating", Mylar and the like...  the record-setting QD solar cells were produced on PEN because it's mechanically better than those other films.  Hence the record, hooray.  You're petitioning for materials with lower tensile strength.   ::)

It is not one hundred times better.
Thickness matters.
Plus, you can't strain it anywhere close to its yield without damaging the cells adhered to it.

You're lifting a tent flap under martian g, not entering a tug-of-war competition.  :D

Offline oiorionsbelt

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Re: Space Solar Power with BFR
« Reply #113 on: 06/10/2018 05:27 pm »
Maybe it needs to be laminated on a 50 micrometer mylar sheet.

You might also consider Gorilla Glass...

Perhaps aluminium foil backing and plastic over coating?

So as you see, QD solar cells don't require glass, Gorilla or other.  Multiple industrial examples make that clear enough.

As for aluminum foil, "plastic over coating", Mylar and the like...  the record-setting QD solar cells were produced on PEN because it's mechanically better than those other films.  Hence the record, hooray.  You're petitioning for materials with lower tensile strength.   ::)
Cost is more important though. Aluminium and/or glass made on Mars might well be cheaper than mylar type films imported from Earth.

But in space, you'd probably have nothing, with the solar film spread over carbon fibre trusses.

Offline LMT

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Re: Space Solar Power with BFR
« Reply #114 on: 06/10/2018 06:42 pm »
Maybe it needs to be laminated on a 50 micrometer mylar sheet.

You might also consider Gorilla Glass...

Perhaps aluminium foil backing and plastic over coating?

So as you see, QD solar cells don't require glass, Gorilla or other.  Multiple industrial examples make that clear enough.

As for aluminum foil, "plastic over coating", Mylar and the like...  the record-setting QD solar cells were produced on PEN because it's mechanically better than those other films.  Hence the record, hooray.  You're petitioning for materials with lower tensile strength.   ::)
Cost is more important though. Aluminium and/or glass made on Mars might well be cheaper than mylar type films imported from Earth.

But in space, you'd probably have nothing, with the solar film spread over carbon fibre trusses.

?  QD solar cells are designed to be cheap.  It's a selling point, e.g. at Quantum Materials / Solterra.  Check out the QD industry; it's interesting.



Quote
SOLAR ENERGY- no carbon emissions, unlimited supply and available to all. This renewable source is one of the answers to energy independence, but has been previously expensive to implement. Now, with advanced automated tetrapod quantum dot manufacturing, both cost and efficiency concerns are addressed. Although smaller than living cells, quantum.dots can absorb all wavelengths of visible sunlight plus the UV and Infrared. Using proprietary technologies, Solterra will manufacture very low cost solar cells utilizing Quantum Dot Technology for less than the cost of conventional solar cells. By combining Quantum Materials disruptive technologies of novel synthesis, QDX™ coating and automated production, quantum dot supply problems are solved. Solterra will also use R2R production methods invented by QMC Chief Science Officer, Dr. Ghassan Jabbour, that can be scaled by increasing R2R speeds.

Our third generation quantum dot solar cells do not require custom made, expensive ,nor complex, processing equipment, and we do not use costly silicon or rare earth elements such as indium. Solterra instead will rely on low-cost screen printing and/or inkjet techniques applied to inexpensive substrates. Quantum Dot Solar Cells have extremely high potential efficiency, having demonstrated the production of multiple excitons from a single electron.

Quantum Materials patented quantum dot synthesis, developed by Dr. Michael Wong of Rice University has been acquired by Quantum Materials for Solterra Renewable Technologies, Inc. By combining this proprietary, low cost QD manufacture process with automation QD manufacture, the quantities of tetrapod quantum dots needed to supply the daily use requirements of a solar cell plant production can be scaled into the Gigawatts/year range reducing the cost of solar generated electricity to little more than grid price at today's electricity prices. With grid prices expected to continue to increase, renewable solar energy using QMC Quantum Dot Technology will not only cost less but can also be good for the environment!

Quantum Materials' Solar cells will come to market competitively priced with the opportunity to reduce prices even further as economies of scale come into effect. Additionally we believe our quantum dot manufacturing capability and print based cell manufacturing process will enable the rapid deployment of additional manufacturing sites across the globe.

Offline johnfwhitesell

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Re: Space Solar Power with BFR
« Reply #115 on: 06/10/2018 06:53 pm »
Cost is more important though. Aluminium and/or glass made on Mars might well be cheaper than mylar type films imported from Earth.

I think that the history of space exploration since Apollo shows us that it's far, far cheaper to plan a mission around hardware that is already operational then to plan a mission around hardware you think will work.  If it's 2030 and a prototype aluminium smelter is in operation you can start comparing the cost-benefits of import substitution.  However what will solar power is a rapidly advancing field so who knows what it will look like in 12 years?  Maybe 12 years from now perovskite solar cell printing will be so effective that they can just print solar cells onto gravel and make a solar farm out of that.

Offline meekGee

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Re: Space Solar Power with BFR
« Reply #116 on: 06/10/2018 06:57 pm »
https://www.youtube.com/watch?time_continue=72&v=_J4RxDZJ6Vg
I've never heard that one before.

Musk was asked about solar, and seems very far from certain or enthusiastic. He describes one concept they evaluated, brings up nuclear, and says solar is "very important", as opposed to using any stronger description like "is the way to produce power on Mars".

Hmmm.

-----
ABCD: Always Be Counting Down

ABCD - Always Be Counting Down

Offline LMT

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Re: Space Solar Power with BFR
« Reply #117 on: 06/12/2018 07:26 pm »
https://www.youtube.com/watch?time_continue=72&v=_J4RxDZJ6Vg
I've never heard that one before.

Musk was asked about solar, and seems very far from certain or enthusiastic. He describes one concept they evaluated, brings up nuclear, and says solar is "very important", as opposed to using any stronger description like "is the way to produce power on Mars".

Hmmm.

-----
ABCD: Always Be Counting Down

I think he's alluding to the challenge of power in winter, when daily PV power output is very low.  For example in Hellas Basin daily insolation is < 15% of summer max.   Also at winter temperatures quantum dot solar cell power conversion efficiency may drop a bit, further reducing PV output (Speirs et al. 2016).

Considering the power requirement of a permanent SpaceX facility, creativity is needed, both for winter power production and also for scalable long-term storage.  Else very large and perhaps prohibitively expensive nuclear power plants will be needed.

For comparison:  NASA JSC Lunar Surface Concept Study - Lunar Energy Storage.   This trade study evaluated conceivable options for lunar night power production and storage.  Scaling those options to, say, 100 MW in martian winter would be a challenge.   For example the study's notional cryogenic regenerative fuel cells had an exceptional theoretical rating of 4.1 MJ/kg.  Assuming such a system could be realized, to deliver 100 MW through 16 winter night hours the fuel cell cargo would comprise ~ 10 ITS payloads.  Presumably the required LH2 and LOX (liquids comprising ~ 70% of system mass) would be obtained using propellant plant equipment.

Scaling the winter power source to provide the (excess) stored terajoules presents its own challenges of course.

And this is just a fair-weather overnight scenario.  A regional dust storm lasting several days would likely overwhelm a system of this scale.

--

One option for small improvement:  add duplicate PV power plants up to 2000 km east and west of the SpaceX facility, and up to 2000 km toward the equator.  Each plant is connected to the grid via thin, low-temperature HVDC power lines, which have high efficiency to that distance. 

Duplication boosts power of course, albeit with considerable extra mass.  The equatorial plant maximizes daily production.  More importantly, at such great separation, on almost every day at least one plant enjoys clear skies, for vital redundancy.  Also the longitudinal separation extends power production slightly past facility-local sunset and sunrise, but not overnight.



Refs

Speirs, M. J., Dirin, D. N., Abdu-Aguye, M., Balazs, D. M., Kovalenko, M. V., & Loi, M. A. (2016). Temperature dependent behaviour of lead sulfide quantum dot solar cells and films. Energy & Environmental Science, 9(9), 2916-2924.
« Last Edit: 06/13/2018 04:25 am by LMT »

Offline CuddlyRocket

Re: Space Solar Power with BFR
« Reply #118 on: 06/13/2018 10:00 pm »
One option for small improvement:  add duplicate PV power plants up to 2000 km east and west of the SpaceX facility, and up to 2000 km toward the equator.  Each plant is connected to the grid via thin, low-temperature HVDC power lines, which have high efficiency to that distance.

2,000 kilometers - a small improvement?

Offline Tulse

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Re: Space Solar Power with BFR
« Reply #119 on: 06/14/2018 02:36 pm »
Doesn't Opportunity's situation put paid to the notion of using solar as the power source for a settlement?  If dust storms can radically reduce insolation for weeks at a time, wouldn't that seriously endanger a base?  Are there practical back-up systems/energy storage solutions that could cover that amount of time with severely reduced PV output?

Offline envy887

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Re: Space Solar Power with BFR
« Reply #120 on: 06/14/2018 02:47 pm »
Doesn't Opportunity's situation put paid to the notion of using solar as the power source for a settlement?
No.

Quote
If dust storms can radically reduce insolation for weeks at a time, wouldn't that seriously endanger a base?
No, not a properly planned one.

Quote
Are there practical back-up systems/energy storage solutions that could cover that amount of time with severely reduced PV output?

Yes. The PV required for making fuel is several megawatts per BFS. Even severely reduced, it should be plenty to run critical systems. You wouldn't make fuel in a dust storm.

Even if the storm is bad enough that the PV is unable to keep critical functions running and the batteries charged, each BFS is a giant chemical battery holding about a megawatt-year of energy. Simply run boiloff through a small LNG genset and you have power, water, and heat.

Offline Tulse

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Re: Space Solar Power with BFR
« Reply #121 on: 06/14/2018 02:50 pm »
So, in other words, because of the power needs of ISRU, the settlement will be vastly overpowered for its non-ISRU needs?

Offline guckyfan

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Re: Space Solar Power with BFR
« Reply #122 on: 06/14/2018 02:52 pm »
Much depends on data gathered now. Is the extreme Tau value short lived and local or can a dust storm have those values for extended times in one location? Up to now the state of information was that even during major dust storms solar would yield at least 20% of normal values which would be enough by far to keep essential services running. Just power down all major power consuming industrial processes.

Offline LMT

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Re: Space Solar Power with BFR
« Reply #123 on: 06/14/2018 05:00 pm »
even during major dust storms solar would yield at least 20% of normal values which would be enough by far to keep essential services running.

"Mars is hard."

And even harder than you indicated.  The 2007 dust storm's atmospheric light transmission was < 5% for a period of ~ 3 weeks above Spirit, and ~ 4 weeks above Opportunity.  Shutdown.  Lemmon et al. 2015, Fig. 8.

At a SpaceX facility "essential services" would be more than just a system clock.  Propellant plant services, for example, and unavoidably.  Earth-return launch windows must be honored, irrespective of weather or season.  Winter storms occur:  power systems must have scale and redundancy to accommodate.

Hard, isn't it?



Quote
"After the last of these images were taken, Opportunity was forced to halt imaging -- and most other operations, including regular communication with Earth -- to conserve its battery power and ride out the storm."

Refs

Lemmon, M. T., Wolff, M. J., Bell III, J. F., Smith, M. D., Cantor, B. A., & Smith, P. H. (2015). Dust aerosol, clouds, and the atmospheric optical depth record over 5 Mars years of the Mars Exploration Rover mission. Icarus, 251, 96-111.
« Last Edit: 06/14/2018 07:57 pm by LMT »

Offline envy887

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Re: Space Solar Power with BFR
« Reply #124 on: 06/14/2018 06:35 pm »
And even harder than you indicated.  The 2007 dust storm reduced light transmission by more than 95% for a period of ~ 3 weeks above Spirit, and ~ 4 weeks above Opportunity.  Shutdown.  Lemmon et al. 2015, Fig. 8.

At a SpaceX facility "essential services" would be more than just a system clock.  Propellant plant services, for example, and unavoidably.  Earth-return launch windows must be honored, irrespective of weather or season.  Winter storms occur:  power systems must have scale and redundancy to accommodate.

PV power output is not entirely linear with direct optical transmission, since there is indirect light transmission.

And propellant production absolutely DOES NOT have to continue during a dust storm. That's absurd. Just size the system assuming some weeks are lost to a storm, that is only a few percent of the time between synods.

Offline LMT

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Re: Space Solar Power with BFR
« Reply #125 on: 06/14/2018 07:30 pm »
And even harder than you indicated.  The 2007 dust storm reduced light transmission by more than 95% for a period of ~ 3 weeks above Spirit, and ~ 4 weeks above Opportunity.  Shutdown.  Lemmon et al. 2015, Fig. 8.

At a SpaceX facility "essential services" would be more than just a system clock.  Propellant plant services, for example, and unavoidably.  Earth-return launch windows must be honored, irrespective of weather or season.  Winter storms occur:  power systems must have scale and redundancy to accommodate.

PV power output is not entirely linear with direct optical transmission, since there is indirect light transmission.

And propellant production absolutely DOES NOT have to continue during a dust storm. That's absurd. Just size the system assuming some weeks are lost to a storm, that is only a few percent of the time between synods.

When the atmosphere transmits < 5%, nonlinear response and indirect lighting aren't helpful.

You realize those 4 weeks were just the peak of the storm, yes?  The storm ran for 2 months.  In martian winter, off-equator PV would be essentially disabled for the entirety of the storm. 

Imagine 5 months of winter in Hellas Basin, with daily clear-sky PV averaging 10% of summer max.  Then intersperse 3 months of storms, all causing near-complete PV shutdown for the duration.

Quantifying:  What challenge does that scenario present to winter propellant production for, say, 10 spacecraft?  How might you structure and scale things to accomplish the loading?
« Last Edit: 06/15/2018 12:09 am by LMT »

Offline envy887

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Re: Space Solar Power with BFR
« Reply #126 on: 06/14/2018 07:53 pm »
x
And even harder than you indicated.  The 2007 dust storm reduced light transmission by more than 95% for a period of ~ 3 weeks above Spirit, and ~ 4 weeks above Opportunity.  Shutdown.  Lemmon et al. 2015, Fig. 8.

At a SpaceX facility "essential services" would be more than just a system clock.  Propellant plant services, for example, and unavoidably.  Earth-return launch windows must be honored, irrespective of weather or season.  Winter storms occur:  power systems must have scale and redundancy to accommodate.

PV power output is not entirely linear with direct optical transmission, since there is indirect light transmission.

And propellant production absolutely DOES NOT have to continue during a dust storm. That's absurd. Just size the system assuming some weeks are lost to a storm, that is only a few percent of the time between synods.

When the atmosphere transmits < 5%, nonlinear response and indirect lighting aren't helpful.

You realize those 4 weeks were just the peak of the storm, yes?  The storm ran for 2 months.  In martian winter, off-equator PV would be essentially disabled for the entirety of the storm. 

Imagine 5 months of winter in Hellas Basin, with daily clear-sky PV averaging 10% of summer max.  Then intersperse 3 months of storms, all causing near-complete PV shutdown for the duration.

Quantifying:  What challenge does that scenario present to winter propellant production for, say, 10 spacecraft?  How might you structure and scale things to accomplish the loading?

This should probably go in one of the Mars threads, not SSP.

Hellas at mostly 40+ degrees south is probably further than you want to go with solar as primary, and more equatorial locations are better initially. But even there, just make it bigger, and do propellant production mainly in the summer.

Offline LMT

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Re: Space Solar Power with BFR
« Reply #127 on: 06/14/2018 08:13 pm »
Quantifying:  What challenge does that scenario present to winter propellant production for, say, 10 spacecraft?  How might you structure and scale things to accomplish the loading?

Hellas at mostly 40+ degrees south is probably further than you want to go with solar as primary, and more equatorial locations are better initially. But even there, just make it bigger, and do propellant production mainly in the summer.

The quantitative challenge does press hard.  Adding "a few percent" just isn't enough.  So sure, scaling all systems for "feast-or-famine" high-speed summer loading is an option.  It would incur a real mass penalty, but it's an option.

Offline alexterrell

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Re: Space Solar Power with BFR
« Reply #128 on: 11/18/2020 07:28 am »
Not sure if this has been covered, but this thread seems a good place for it:

https://www.fnc.co.uk/discover-frazer-nash/news/frazer-nash-exploring-viability-of-space-based-solar-power-to-help-deliver-net-zero

The UK Government is looking for risky ventures, perhaps to try and compensate for the Brexit damage. They have now commissioned a study into Space Solar Power.

This is relevant to SpaceX because if the cost of launching a solar power station is less than the cost of building the solar arrays, then it might be possible to make a business case for it.

Launch cost = System Weight x Cost per unit mass
Quote
As part of the study, we are looking at the leading three SBSP concepts, from the USA (SPS Alpha), UK (CASSIOPeiA) and China (MR-SPS). SBSP experts John Mankins (USA) and Ian Cash (UK) – the inventors of the first two concepts – are supporting our study.

Offline Slarty1080

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Re: Space Solar Power with BFR
« Reply #129 on: 11/21/2020 01:35 pm »
Not sure if this has been covered, but this thread seems a good place for it:

https://www.fnc.co.uk/discover-frazer-nash/news/frazer-nash-exploring-viability-of-space-based-solar-power-to-help-deliver-net-zero

The UK Government is looking for risky ventures, perhaps to try and compensate for the Brexit damage. They have now commissioned a study into Space Solar Power.

This is relevant to SpaceX because if the cost of launching a solar power station is less than the cost of building the solar arrays, then it might be possible to make a business case for it.

Launch cost = System Weight x Cost per unit mass
Quote
As part of the study, we are looking at the leading three SBSP concepts, from the USA (SPS Alpha), UK (CASSIOPeiA) and China (MR-SPS). SBSP experts John Mankins (USA) and Ian Cash (UK) – the inventors of the first two concepts – are supporting our study.
I can't help but feel the idea will run aground somewhere on the rocks of transmission loss, continually dropping solar panel prices and the technical uncertainties around massive solar arrays in orbit. But we shall see. It's a neat idea but I question the practicality / economics of it.
My optimistic hope is that it will become cool to really think about things... rather than just doing reactive bullsh*t based on no knowledge (Brian Cox)

Offline aero

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Re: Space Solar Power with BFR
« Reply #130 on: 11/21/2020 02:43 pm »
Maybe we'll have to wait for Space Elevator development. Then we could transmit power from space to the surface over transmission lines down the Space Elevator shaft!
Retired, working interesting problems

Offline Anderqual

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Re: Space Solar Power with BFR
« Reply #131 on: 11/21/2020 02:57 pm »
Would it be possible to harvest static electricity generated during dust storms to offset solar loss?

Offline john smith 19

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Re: Space Solar Power with BFR
« Reply #132 on: 11/21/2020 03:34 pm »
I can't help but feel the idea will run aground somewhere on the rocks of transmission loss,
JPL found ways to phase lock cavity magetrons (something that was not believed to be possible) to make low cost high power phased array transmitters in the 1970's.
Quote from: Slarty1080
continually dropping solar panel prices
Which only work during the day. Above 800Km daylight is 24 hours long. At GEO there would be no pointer shifting but much higher losses.
Quote from: Slarty1080
and the technical uncertainties around massive solar arrays in orbit. But we shall see. It's a neat idea but I question the practicality / economics of it.
And yet somehow the ISS stays in orbit.
MCT ITS BFR SS. The worlds first Methane fueled FFSC engined CFRP SS structure A380 sized aerospaceplane tail sitter capable of Earth & Mars atmospheric flight.First flight to Mars by end of 2022 TBC. T&C apply. Trust nothing. Run your own #s "Extraordinary claims require extraordinary proof" R. Simberg."Competitve" means cheaper ¬cheap SCramjet proposed 1956. First +ve thrust 2004. US R&D spend to date > $10Bn. #deployed designs. Zero.

Offline john smith 19

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Re: Space Solar Power with BFR
« Reply #133 on: 11/21/2020 03:36 pm »
Not sure if this has been covered, but this thread seems a good place for it:

https://www.fnc.co.uk/discover-frazer-nash/news/frazer-nash-exploring-viability-of-space-based-solar-power-to-help-deliver-net-zero

The UK Government is looking for risky ventures, perhaps to try and compensate for the Brexit damage. They have now commissioned a study into Space Solar Power.

This is relevant to SpaceX because if the cost of launching a solar power station is less than the cost of building the solar arrays, then it might be possible to make a business case for it.

Launch cost = System Weight x Cost per unit mass
Quote
As part of the study, we are looking at the leading three SBSP concepts, from the USA (SPS Alpha), UK (CASSIOPeiA) and China (MR-SPS). SBSP experts John Mankins (USA) and Ian Cash (UK) – the inventors of the first two concepts – are supporting our study.
And they will probably conclude (as earlier studies did) that without cheap and rapidly reusable launch systems the design is uneconomic.
MCT ITS BFR SS. The worlds first Methane fueled FFSC engined CFRP SS structure A380 sized aerospaceplane tail sitter capable of Earth & Mars atmospheric flight.First flight to Mars by end of 2022 TBC. T&C apply. Trust nothing. Run your own #s "Extraordinary claims require extraordinary proof" R. Simberg."Competitve" means cheaper ¬cheap SCramjet proposed 1956. First +ve thrust 2004. US R&D spend to date > $10Bn. #deployed designs. Zero.

Offline rakaydos

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Re: Space Solar Power with BFR
« Reply #134 on: 11/21/2020 04:15 pm »
Would it be possible to harvest static electricity generated during dust storms to offset solar loss?
There's no way you could be aware, but "Triboelectricity" has a single, violently aggressive supporter on these forums. his evidence is too sketchy to garner any support though. It isnt looking good.

Offline Twark_Main

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Re: Space Solar Power with BFR
« Reply #135 on: 11/21/2020 05:51 pm »
Not sure if this has been covered, but this thread seems a good place for it:

https://www.fnc.co.uk/discover-frazer-nash/news/frazer-nash-exploring-viability-of-space-based-solar-power-to-help-deliver-net-zero

The UK Government is looking for risky ventures, perhaps to try and compensate for the Brexit damage. They have now commissioned a study into Space Solar Power.

This is relevant to SpaceX because if the cost of launching a solar power station is less than the cost of building the solar arrays, then it might be possible to make a business case for it.

Launch cost = System Weight x Cost per unit mass
Quote
As part of the study, we are looking at the leading three SBSP concepts, from the USA (SPS Alpha), UK (CASSIOPeiA) and China (MR-SPS). SBSP experts John Mankins (USA) and Ian Cash (UK) – the inventors of the first two concepts – are supporting our study.

Problem with using SBSP en-masse is and always has been MMOD.

Micrometeoroid impacts blast away ~100x as much mass as the original impactor, and SBSP offers a huge target (you almost couldn't design something worse for MMOD unless you launch buckets of sand or something). So even if you dodge the big chunks, your solar panels will slowly get "eroded away" by untrackable MMOD. Since each impact multiplies the amount of tiny debris, you don't need too many SBSP installations before you're substantially increasing the MMOD environment in your chosen orbit.

Note that while the Kessler syndrome runaway threshold depends only on the total mass in a certain orbit, a large area satellites will be eroded away into fragments faster than a compact satellite.
« Last Edit: 11/21/2020 05:52 pm by Twark_Main »
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Offline Slarty1080

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Re: Space Solar Power with BFR
« Reply #136 on: 11/22/2020 01:05 pm »
I can't help but feel the idea will run aground somewhere on the rocks of transmission loss,
JPL found ways to phase lock cavity magetrons (something that was not believed to be possible) to make low cost high power phased array transmitters in the 1970's.
Quote from: Slarty1080
continually dropping solar panel prices
Which only work during the day. Above 800Km daylight is 24 hours long. At GEO there would be no pointer shifting but much higher losses.
Quote from: Slarty1080
and the technical uncertainties around massive solar arrays in orbit. But we shall see. It's a neat idea but I question the practicality / economics of it.
And yet somehow the ISS stays in orbit.
Yes the ISS stays in orbit, but it does not have "large" solar arrays on the gigawatt scale. The proposed solar plant would be roughly 10,000 times bigger. What could possibly go wrong?
My optimistic hope is that it will become cool to really think about things... rather than just doing reactive bullsh*t based on no knowledge (Brian Cox)

Offline M.E.T.

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Re: Space Solar Power with BFR
« Reply #137 on: 11/22/2020 01:20 pm »
Not sure if this has been covered, but this thread seems a good place for it:

https://www.fnc.co.uk/discover-frazer-nash/news/frazer-nash-exploring-viability-of-space-based-solar-power-to-help-deliver-net-zero

The UK Government is looking for risky ventures, perhaps to try and compensate for the Brexit damage. They have now commissioned a study into Space Solar Power.

This is relevant to SpaceX because if the cost of launching a solar power station is less than the cost of building the solar arrays, then it might be possible to make a business case for it.

Launch cost = System Weight x Cost per unit mass
Quote
As part of the study, we are looking at the leading three SBSP concepts, from the USA (SPS Alpha), UK (CASSIOPeiA) and China (MR-SPS). SBSP experts John Mankins (USA) and Ian Cash (UK) – the inventors of the first two concepts – are supporting our study.

Problem with using SBSP en-masse is and always has been MMOD.

Micrometeoroid impacts blast away ~100x as much mass as the original impactor, and SBSP offers a huge target (you almost couldn't design something worse for MMOD unless you launch buckets of sand or something). So even if you dodge the big chunks, your solar panels will slowly get "eroded away" by untrackable MMOD. Since each impact multiplies the amount of tiny debris, you don't need too many SBSP installations before you're substantially increasing the MMOD environment in your chosen orbit.

Note that while the Kessler syndrome runaway threshold depends only on the total mass in a certain orbit, a large area satellites will be eroded away into fragments faster than a compact satellite.

Interesting. Does this then, by extrapolation, ultimately invalidate the idea of a Dyson swarm as well?

Offline savantu

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Re: Space Solar Power with BFR
« Reply #138 on: 11/22/2020 01:40 pm »
In my view solar power is irrelevant long term for space activities. You need nuclear. Hopefully the renaissance of nuclear invest for low power reactors on ground/space will do to BEO exploration what Spx did to transportation.
The first attempts to Mars will be solar, but their multitude of issues already mentioned will probably mean by 2025 you're launching disassembled reactors and getting them online in space.

Offline Twark_Main

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Re: Space Solar Power with BFR
« Reply #139 on: 11/23/2020 12:20 am »
Interesting. Does this then, by extrapolation, ultimately invalidate the idea of a Dyson swarm as well?

I would think so. :(


by 2025 you're launching... reactors

Are there any reactor programs that have a prayer of being ready by then?
« Last Edit: 11/23/2020 12:20 am by Twark_Main »
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Offline KelvinZero

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Re: Space Solar Power with BFR
« Reply #140 on: 11/23/2020 12:52 am »
Wouldn't this argument against solar power in space also apply to space nuclear power? They also need large  surface areas to radiate away heat. Im not sure if they all circulate liquids through the radiators but wouldn't that make them particularly vulnerable?

Offline LMT

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Re: Space Solar Power with BFR
« Reply #141 on: 11/23/2020 03:11 am »
Not sure if this has been covered, but this thread seems a good place for it:

https://www.fnc.co.uk/discover-frazer-nash/news/frazer-nash-exploring-viability-of-space-based-solar-power-to-help-deliver-net-zero

The UK Government is looking for risky ventures, perhaps to try and compensate for the Brexit damage. They have now commissioned a study into Space Solar Power.

This is relevant to SpaceX because if the cost of launching a solar power station is less than the cost of building the solar arrays, then it might be possible to make a business case for it.

Launch cost = System Weight x Cost per unit mass
Quote
As part of the study, we are looking at the leading three SBSP concepts, from the USA (SPS Alpha), UK (CASSIOPeiA) and China (MR-SPS). SBSP experts John Mankins (USA) and Ian Cash (UK) – the inventors of the first two concepts – are supporting our study.

Problem with using SBSP en-masse is and always has been MMOD [micrometeoroids and orbital debris].

That's one of the advantages of piggybacking SSP on an ISEP VLEO Terrestation structure.  Required SSP area is ~ 10,000x smaller than the area required by Frazer-Nash geosynchronous SSP, due to inverse square propagation and VLEO night shutdown.

Hence, Terrestation SSP debris strike area is roughly 10,000x smaller.

Dedicated Terrestation SSP system mass is at least 10,000x less, also.
« Last Edit: 11/23/2020 03:58 am by LMT »

Offline john smith 19

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Re: Space Solar Power with BFR
« Reply #142 on: 11/23/2020 07:14 am »
Are there any reactor programs that have a prayer of being ready by then?
Kilopower might be ready for a field trial.

MCT ITS BFR SS. The worlds first Methane fueled FFSC engined CFRP SS structure A380 sized aerospaceplane tail sitter capable of Earth & Mars atmospheric flight.First flight to Mars by end of 2022 TBC. T&C apply. Trust nothing. Run your own #s "Extraordinary claims require extraordinary proof" R. Simberg."Competitve" means cheaper ¬cheap SCramjet proposed 1956. First +ve thrust 2004. US R&D spend to date > $10Bn. #deployed designs. Zero.

Offline savantu

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Re: Space Solar Power with BFR
« Reply #143 on: 11/23/2020 10:14 am »
Are there any reactor programs that have a prayer of being ready by then?
Kilopower might be ready for a field trial.
The product follows the need. Until today, why would anyone invest in nuclear space power? The only customer could be once in a decade probe of Nasa which might or might not come.

With real plans to set up bases on the moon & Mars there is a real need & market for such devices. I'd be really surprised if a leading space transportation company doesn't have an internal development program or at least ordered some.
« Last Edit: 11/23/2020 10:58 am by savantu »

Offline john smith 19

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Re: Space Solar Power with BFR
« Reply #144 on: 11/24/2020 08:31 pm »
The product follows the need. Until today, why would anyone invest in nuclear space power? The only customer could be once in a decade probe of Nasa which might or might not come.
Unless it was designed to be scalable from the needs of a largish outer planets probe (say 1Kw) to powering the ion drives that could send probes to and planet in the inner or outer system substantially faster than they can now be sent.

Which Kilopower is designed to do.
Quote from: savantu
With real plans to set up bases on the moon & Mars there is a real need & market for such devices. I'd be really surprised if a leading space transportation company doesn't have an internal development program or at least ordered some.
SX have talked about it. IIRC what they've said is it's hard to do reactor development work.
 Historically space nuclear systems have gone with HEU (or "bomb grade") fuel. This makes the USG very twitchy about anyone doing any work in this area that is not under their direct control.

You might like to look at the Kilopower threads in the Advanced Concepts section.
MCT ITS BFR SS. The worlds first Methane fueled FFSC engined CFRP SS structure A380 sized aerospaceplane tail sitter capable of Earth & Mars atmospheric flight.First flight to Mars by end of 2022 TBC. T&C apply. Trust nothing. Run your own #s "Extraordinary claims require extraordinary proof" R. Simberg."Competitve" means cheaper ¬cheap SCramjet proposed 1956. First +ve thrust 2004. US R&D spend to date > $10Bn. #deployed designs. Zero.

Offline Twark_Main

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Re: Space Solar Power with BFR
« Reply #145 on: 11/24/2020 11:29 pm »
Wouldn't this argument against solar power in space also apply to space nuclear power? They also need large  surface areas to radiate away heat. Im not sure if they all circulate liquids through the radiators but wouldn't that make them particularly vulnerable?

Generally space nuclear is all about operation in deep space far from the Sun, not generating electricity in LEO and beaming it to the Earth. MMOD is really an issue in LEO (and GEO, to a lesser extent).
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Offline LMT

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Re: Space Solar Power with BFR
« Reply #146 on: 11/26/2020 04:28 pm »
MMOD is really an issue in LEO (and GEO, to a lesser extent).

VLEO and GEO have similar cataloged debris fluxes.  However, true GEO flux is likely higher:

Quote from: National Research Council
The main distinction between the populations of cataloged and uncataloged large debris is more a product of sensor capabilities than of any inherent differences in the objects. For example, a fragment 30 cm in diameter that would almost certainly be cataloged if it were in LEO would not be cataloged if it were in GEO.

Debris is not a critical issue for VLEO SSP due to low flux and small required SSP area.  SSP area in GEO is ~ 10,000x larger, hence the debris issue.

GEO-scale cost likely disqualifies first.

Image:  Orbital debris: A technical assessment, Fig. 3-3.  "Spatial density of the 1994 U.S. Space Command Satellite Catalog."

Refs.

National Research Council, 1995. Orbital debris: A technical assessment. National Academies Press.
« Last Edit: 11/26/2020 05:09 pm by LMT »

Offline Twark_Main

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Re: Space Solar Power with BFR
« Reply #147 on: 11/28/2020 09:38 pm »
VLEO and GEO have similar cataloged debris fluxes.

According to your own (outdated) chart, the density in LEO is 100x what it is in GEO. Flux equals density times orbital velocity, so the flux difference in LEO vs GEO is even larger.

SSP area in GEO is ~ 10,000x larger, hence the debris issue.

Your source (buried two links deep) is yourself, hand-waving with the inverse square law Friis formula.

However I know of no actual proposals where they take a LEO SSP design and relocate it to GEO without any redesign (a proposal which, according to your own numbers, would be at most 0.001% efficient; yes sunlight in space is abundant, but equipment is not).

Is this 10,000x number actually based on a serious SSP proposal that I somehow missed, or just a figment of imagination?
« Last Edit: 12/04/2020 02:26 pm by Twark_Main »
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Offline LMT

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Re: Space Solar Power with BFR
« Reply #148 on: 11/29/2020 06:45 am »
VLEO and GEO have similar cataloged debris fluxes.

According to your own (outdated) chart, the density in LEO is 100x what it is in GEO. Flux equals density times orbital velocity, so the flux difference in LEO vs GEO is even larger.

VLEO, not LEO.

VLEO (250 km) density is much lower than LEO density: only ~ 1E-11.  Multiply by VLEO/GEO velocity ratio 2.5, and you see flux is similar, as I said. 

That's for cataloged debris, and again, as the NRC emphasized, the GEO catalog is incomplete.  True GEO flux is likely higher.

Or do you think invisible 30 cm debris is harmless in GEO?

--
Your source (buried two links deep) is yourself, hand-waving with the inverse square law.

However I know of no actual proposals where they take a LEO SSP design and relocate it to GEO without any redesign (a proposal which, according to your own numbers, would be at most 0.001% efficient; yes sunlight in space is abundant, but equipment is not).

Is this 10,000x number actually based on a serious SSP proposal that I somehow missed, or just a figment of imagination?

Weird.  No, I posted the Friis formula right here.  A given SSP system delivers ~ 10,000x more power from VLEO than from GEO, due to inverse square propagation, and subtracting VLEO night shutdown. 

It's a fundamental SSP calc.
« Last Edit: 11/29/2020 06:46 am by LMT »

Offline RonM

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Re: Space Solar Power with BFR
« Reply #149 on: 11/29/2020 12:49 pm »
There are several problems with VLEO solar power. Atmospheric drag on large solar panel arrays will be high and require a lot of effort to maintain altitude. Receiving rectenna will only see a satellite for a short time, so the satellite constellation would need thousands of satellites. One of the biggest advantages of space based solar power is near constant sunlight and VLEO throws that away. It would be far easier and cheaper to install solar panels where needed on Earth.

Offline LMT

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Re: Space Solar Power with BFR
« Reply #150 on: 11/29/2020 04:03 pm »
There are several problems with VLEO solar power. Atmospheric drag on large solar panel arrays will be high and require a lot of effort to maintain altitude. Receiving rectenna will only see a satellite for a short time, so the satellite constellation would need thousands of satellites. One of the biggest advantages of space based solar power is near constant sunlight and VLEO throws that away. It would be far easier and cheaper to install solar panels where needed on Earth.

The SSP comparison was VLEO to GEO.  You see why the Friis formula very strongly favors VLEO over GEO, yes?

Then you look at other trade-offs:

- Drag:  Yes, VLEO drag is high.  ISEP can counter VLEO drag without propellant, by design.

- Coverage:  Equatorial regional-grid rectennae would maximize coverage.  E.g., an idealized set of ~ 22 equatorial rectennae would position 22 VLEO SSP sats ~ 4 min apart for full daytime regional grid coverage.  Ocean gaps and future global power grid possibilities are further factors.

- Panels on Earth:  At small scale, yes, panels are cheaper on Earth.  SSP is often analyzed at great commercial scale, where e.g. land use becomes a factor. 
« Last Edit: 11/29/2020 04:06 pm by LMT »

Offline mandrewa

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Re: Space Solar Power with BFR
« Reply #151 on: 11/29/2020 06:01 pm »
There's something I don't understand about the Friis Transmission Formula.  One meter is the longest microwave frequency.  If I plug 1 meter into the formula and assume the distance between the antennas is 250 km and then apply this to the Friis Formula I get a ratio of power received to power transmitted that is equal to (1.01 * 10^-13) times the gain of the first antenna times the gain of the second antenna. 

Unless those gains are absurdly high that means only an absurdly low percent of the energy is being transmitted.

What are typical gain numbers for these antennas?

Offline mandrewa

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Re: Space Solar Power with BFR
« Reply #152 on: 11/30/2020 03:04 pm »
So thinking more about this I realized that regardless of whether the Friis Transmission Equation is the correct equation to apply to this context, there is a better way to think about it.

Imagine a cone.  The microwave emitter is not a point source radiating in all directions.  It is trying to emit all of the photons (and their energy) in one direction.  But that beam is going to spread.  So our emitter is the tip of this cone and the receiving antenna will be at the base of the cone.  High transmission efficiencies demand that the receiving antenna be the same size or larger than the cone created by the slowing spreading microwave photons.

And therefore the size of the receiving antenna that we need in order to get high transmission efficiencies gets four times larger for every doubling of distance.

So the size of the receiving antenna needed if the energy is coming from an emitter in GEO is vastly larger than if it's coming from LEO.

So this reinforces what LMT has said above and it may be that I've just restated the Friis Transmission Equation in a different form (or a particular case covered by that equation) but even so I prefer thinking about it in terms of cones.  And one of the benefits of thinking about it this way is that it suggests a possible solution to this problem.

Here's the key question.  How efficient can we get at doing microwave energy transmission in space?  Because if we can get really efficient, like say 99%, then we can imagine a chain of intermediate receiving and emitting stations that can conduct energy from one point to another with relatively little loss.

So if we can do 99% for one step, and there were ten steps, that's 0.99^10, aka 90% efficiency over that total distance.  And the larger the receiving antenna, the larger the distance covered by a particular step.

Anyways this is just speculation.  But I do have the impression, or an idea I got somewhere, that very high efficiencies are possible for microwave energy transmission in the ideal case.

« Last Edit: 11/30/2020 03:12 pm by mandrewa »

Offline Slarty1080

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Re: Space Solar Power with BFR
« Reply #153 on: 11/30/2020 04:56 pm »
So thinking more about this I realized that regardless of whether the Friis Transmission Equation is the correct equation to apply to this context, there is a better way to think about it.

Imagine a cone.  The microwave emitter is not a point source radiating in all directions.  It is trying to emit all of the photons (and their energy) in one direction.  But that beam is going to spread.  So our emitter is the tip of this cone and the receiving antenna will be at the base of the cone.  High transmission efficiencies demand that the receiving antenna be the same size or larger than the cone created by the slowing spreading microwave photons.

And therefore the size of the receiving antenna that we need in order to get high transmission efficiencies gets four times larger for every doubling of distance.

So the size of the receiving antenna needed if the energy is coming from an emitter in GEO is vastly larger than if it's coming from LEO.

So this reinforces what LMT has said above and it may be that I've just restated the Friis Transmission Equation in a different form (or a particular case covered by that equation) but even so I prefer thinking about it in terms of cones.  And one of the benefits of thinking about it this way is that it suggests a possible solution to this problem.

Here's the key question.  How efficient can we get at doing microwave energy transmission in space?  Because if we can get really efficient, like say 99%, then we can imagine a chain of intermediate receiving and emitting stations that can conduct energy from one point to another with relatively little loss.

So if we can do 99% for one step, and there were ten steps, that's 0.99^10, aka 90% efficiency over that total distance.  And the larger the receiving antenna, the larger the distance covered by a particular step.

Anyways this is just speculation.  But I do have the impression, or an idea I got somewhere, that very high efficiencies are possible for microwave energy transmission in the ideal case.
Does this mean we can replace all the high voltage transmission lines? Or has the maths gone wrong somewhere?
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Offline LMT

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Re: Space Solar Power with BFR
« Reply #154 on: 11/30/2020 05:51 pm »
I do have the impression, or an idea I got somewhere, that very high efficiencies are possible for microwave energy transmission...

The Friis formula gives max transmission over any appreciable distance (far field).

Image:  a worked example, Sophocles 2003, Ex. 16.6.1.

You might rework the example to illustrate: 

1.  shift to VLEO (250 km)

2.  apply plausible SSP frequency and gain numbers

3.  scale to some commercial gigawatts

Refs.

Sophocles, J., 2003. Electromagnetic waves and antennas.
« Last Edit: 12/01/2020 04:16 pm by LMT »

Offline mandrewa

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Re: Space Solar Power with BFR
« Reply #155 on: 11/30/2020 06:01 pm »
So thinking more about this I realized that regardless of whether the Friis Transmission Equation is the correct equation to apply to this context, there is a better way to think about it.

Imagine a cone.  The microwave emitter is not a point source radiating in all directions.  It is trying to emit all of the photons (and their energy) in one direction.  But that beam is going to spread.  So our emitter is the tip of this cone and the receiving antenna will be at the base of the cone.  High transmission efficiencies demand that the receiving antenna be the same size or larger than the cone created by the slowing spreading microwave photons.

And therefore the size of the receiving antenna that we need in order to get high transmission efficiencies gets four times larger for every doubling of distance.

So the size of the receiving antenna needed if the energy is coming from an emitter in GEO is vastly larger than if it's coming from LEO.

So this reinforces what LMT has said above and it may be that I've just restated the Friis Transmission Equation in a different form (or a particular case covered by that equation) but even so I prefer thinking about it in terms of cones.  And one of the benefits of thinking about it this way is that it suggests a possible solution to this problem.

Here's the key question.  How efficient can we get at doing microwave energy transmission in space?  Because if we can get really efficient, like say 99%, then we can imagine a chain of intermediate receiving and emitting stations that can conduct energy from one point to another with relatively little loss.

So if we can do 99% for one step, and there were ten steps, that's 0.99^10, aka 90% efficiency over that total distance.  And the larger the receiving antenna, the larger the distance covered by a particular step.

Anyways this is just speculation.  But I do have the impression, or an idea I got somewhere, that very high efficiencies are possible for microwave energy transmission in the ideal case.
Does this mean we can replace all the high voltage transmission lines? Or has the maths gone wrong somewhere?

You need straight lines of sight but the surface of the Earth is curved.  So that's a big problem.

You need large antennas (rising vertically), but in a 1 g field, that means an implausible expensive antenna.  That's the second big problem.

That's two big problems and that's enough to explain why energy is not commonly transmitted by microwaves on the surface of the Earth.
« Last Edit: 11/30/2020 06:02 pm by mandrewa »

Offline mandrewa

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Re: Space Solar Power with BFR
« Reply #156 on: 11/30/2020 06:22 pm »
I do have the impression, or an idea I got somewhere, that very high efficiencies are possible for microwave energy transmission...

The Friis formula gives max transmission over any appreciable distance (far field).

Image:  a worked example, Sophocles 2003, Ex. 16.6.1.

You might rework the example to illustrate: 

1.  shift to VLEO (250 km)

2.  apply plausible SSP frequency and gain numbers

3.  scale to some commercial gigawatts

Refs.

Sophocles, J., 2003. Electromagnetic waves and antennas.


Yes, I got that.  That's what I meant when I wrote Reply #151, and plugged in a few numbers and got an absurdly low level of energy transmission.

So how do we explain the idea of solar power satellites?

a) Is it a big math error that people have been making for decades and somehow never noticed despite it being kind of obvious?

b) Or could it be that the Friis Transmission Equation doesn't apply to an antenna emitting a directed beam?

c) Or could it be that you are being perverse by giving an example that is inappropriate and not helpful?  Because although there is nothing wrong with that example per se, I wonder if maybe it has little to do with the particular application of the Friis Transmission Equation to solar power satellites because of the very different circumstances of that context.

Offline LMT

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Re: Space Solar Power with BFR
« Reply #157 on: 11/30/2020 06:29 pm »
could it be that the Friis Transmission Equation doesn't apply to an antenna emitting a directed beam?

No, it works as-is.  Use a practical microwave, e.g. 5.8 GHz (5.2 cm), and try variations.  Transmission efficiency is never like a power line of course, but some variations work better than others.

Offline mandrewa

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Re: Space Solar Power with BFR
« Reply #158 on: 11/30/2020 06:42 pm »
could it be that the Friis Transmission Equation doesn't apply to an antenna emitting a directed beam?

No, it works as-is.  Use a practical microwave, e.g. 5.8 GHz (5.2 cm), and try variations.  Transmission efficiency is never like a power line of course, but some variations work better than others.

Yes.  I guessed it did.  I'm glad to have that verified.  But I'm learning this as I go.

I'm sure you know this, but I'll explain for anyone else that may be reading this why it is that the textbook problem and answer that you gave isn't obviously relevant.

The textbook problem is a broadcast satellite spraying photons over a huge area.  The antennas picking up those photons care about the signal or the information being carried by the photons and not the energy being transferred.  Of course these antennas only receive a tiny fraction of the energy emitted by the broadcast satellite.

Now it's a different situation when your antenna is sized to receive all of the photons being emitted at the other end of the cone.

Offline whitelancer64

Re: Space Solar Power with BFR
« Reply #159 on: 11/30/2020 07:23 pm »
Yes, I got that.  That's what I meant when I wrote Reply #151, and plugged in a few numbers and got an absurdly low level of energy transmission.

So how do we explain the idea of solar power satellites?

*snip*

It is a known issue. SSP has always hinged on having enormous square kilometerage of solar panels, producing lots and lots of power, with a very large receiving antenna on the ground to soak up as much as possible in spite of the huge conversion and transmission losses.
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Re: Space Solar Power with BFR
« Reply #160 on: 12/03/2020 03:33 am »
Applying HAP Microwave Power Transmission to VLEO SSP

High-altitude-platform (HAP) microwave power transmission analysis can be applied to VLEO SSP.

In VLEO SSP we'd reverse conventional HAP beam direction.  Here the HAP features a rectenna on its upper surface, and microwaves are beamed down to the HAP from VLEO.  A thin superconducting tether could transmit the converted power efficiently from the HAP to the surface, where the tether would tie into the regional power grid.  As before, equatorial rectennae would maximize coverage.

HAP points to SSP variations that boost transmission efficiency:

1.  At VLEO range, practical transmission is possible near the limit of the near field (fraunhofer distance), which is the point at which inverse square energy dispersion begins.

Image:  Gavan and Tapuchi 2010, Fig. 2.  Dispersion zones for microwave beam.

2.  A HAP is stratospheric, in dry air.  This permits use of high-frequency microwaves:  e.g., 94 GHz.

3.  Arguably, a well-controlled HAP transmission system can prevent leakage of appreciable microwave power to the surface.  This raises the possibility of power density at the technical limits of transmitter and rectenna, far beyond the standard 100 W/m2 safety limit for controlled surface environments.

Example:

Applying Section 8.3 of Gavan and Tapuchi 2010, with VLEO SSP parameters:

- targeting 95% power transmission efficiency (tau 2) [Gavan and Tapuchi 2010, Fig. 12]

- calculating for min transmission distance of 230 km  (20 km HAP rectenna, 250 km VLEO SSP transmitter)

- 94 GHz (0.003189 m) microwaves

- Rectenna area 2x transmitter area

Result:

Transmitter diameter:  36.3 m

Rectenna diameter:  51.3 m

Refs.

Gavan, J. and Tapuchi, S., 2010. Microwave wireless-power transmission to high-altitude-platform systems. The Radio Science Bulletin, 334, pp.25-42.
« Last Edit: 12/26/2020 04:31 pm by LMT »

Offline Twark_Main

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Re: Space Solar Power with BFR
« Reply #161 on: 12/03/2020 04:12 am »
VLEO and GEO have similar cataloged debris fluxes.

According to your own (outdated) chart, the density in LEO is 100x what it is in GEO. Flux equals density times orbital velocity, so the flux difference in LEO vs GEO is even larger.

VLEO, not LEO.

Ahh, thanks. I missed that.

Or do you think invisible 30 cm debris is harmless in GEO?

What in God's green Earth would make you think that? lol

Your source (buried two links deep) is yourself, hand-waving with the inverse square law.

However I know of no actual proposals where they take a LEO SSP design and relocate it to GEO without any redesign (a proposal which, according to your own numbers, would be at most 0.001% efficient; yes sunlight in space is abundant, but equipment is not).

Is this 10,000x number actually based on a serious SSP proposal that I somehow missed, or just a figment of imagination?

Weird.  No, I posted the Friis formula right here.  A given SSP system delivers ~ 10,000x more power from VLEO than from GEO, due to inverse square propagation, and subtracting VLEO night shutdown. 

It's a fundamental SSP calc.

Given that you never answered my question, I can only assume this "10,000x" larger station was never seriously proposed by anyone, and is nothing but a hypothetical napkin math strawman.
« Last Edit: 12/03/2020 04:22 am by Twark_Main »
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Offline LMT

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Re: Space Solar Power with BFR
« Reply #162 on: 12/03/2020 05:26 am »
I can only assume this "10,000x" larger station was never seriously proposed by anyone, and is nothing but a hypothetical napkin math strawman.

Now you know the Friis formula, so you can see why no one is "hand-waving with the inverse square law".   ::)

Offline Oersted

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Re: Space Solar Power with BFR
« Reply #163 on: 12/03/2020 11:19 am »
@Twark_Main and @LMT, your constant mutual sniping is really tiresome for everybody else to read. You are in a public forum. It's basically the equivalent of standing in the street and arguing at 3am and waking up the whole neighbourhood. Please.   

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Re: Space Solar Power with BFR
« Reply #164 on: 12/03/2020 04:50 pm »
@Twark_Main and @LMT, your constant mutual sniping is really tiresome for everybody else to read. You are in a public forum. It's basically the equivalent of standing in the street and arguing at 3am and waking up the whole neighbourhood. Please.

Sorry for waking you up, Oersted.  What did you make of that HAP SSP application, btw?  Power density maximization and beam steering efficiency are areas that could be examined.

Offline Twark_Main

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Re: Space Solar Power with BFR
« Reply #165 on: 12/04/2020 02:18 pm »
Now you know the Friis formula, so you can see why no one is "hand-waving with the inverse square law".   ::)

Edited to "hand-waving with the Friis formula," so the argument is settled. Show's over, guys. Easy as pulling teeth!

@Twark_Main and @LMT, your constant mutual sniping is really tiresome for everybody else to read. You are in a public forum. It's basically the equivalent of standing in the street and arguing at 3am and waking up the whole neighbourhood. Please.

I too am quite tired of it, if it's any consolation. My apologies.

edit: We got lost down the conversation rabbit-hole, so I never articulated my original point. Maybe that's why our conversation struck some members as nothing more than "arguing at 3am."

It was said that the problem with SSP in GEO is MMOD, but that strikes me as an inaccurate characterization. The problem with SSP in GEO is inefficiency. No sane engineer performs the calculation, arrives at 0.01% energy efficiency (for a power system, no less) and responds, "whelp, no problem there, I'll just rescale it 10,000x bigger!" only later to rule out the design over (of all things) MMOD concerns. To call this a MMOD problem is bend-over-backwards logic, since inefficiency kills GEO SSP long before MMOD gets the chance. ;)

That's all. That's it. All-in-all a minor nitpick, and not nearly worth the grief, I'd say. But we made it this far, so we might as well get something out of it, rather than nothing.

That's the last I'll speak on the subject, so LMT can get the last word. Ad astra, friends!
« Last Edit: 12/06/2020 03:04 am by Twark_Main »
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Offline LMT

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Re: Space Solar Power with BFR
« Reply #166 on: 12/13/2020 09:31 pm »
Possible SpaceX Indonesia Launch Site - Equatorial Applications

Bloomberg 12/12/20
Quote
"Indonesia invited SpaceX to assess the possibility of setting up a rocket launch site in the country, according to a ministry statement.

President Joko Widodo discussed the idea with SpaceX founder Elon Musk during a phone call on Friday, the Coordinating Ministry for Maritime and Investment Affairs said in the statement. Musk intends to send a team to Indonesia in January to study partnership opportunities, it said."

Indonesia's considering a new equatorial launch site in Biak, Papua, offering optimized GEO and ELEO launch.

It would also be optimized for efficient EVLEO SSP / Terrestation launch, conceivably. 

Yet Starships could hop from Boca Chica to existing equatorial South American launch sites; so near-term, South America would seem more practical, in that respect.  Maybe SpaceX is interested in the potential for Indonesian Tesla manufacturing tie-in.
« Last Edit: 12/14/2020 02:54 am by LMT »

Offline Robotbeat

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Re: Space Solar Power with BFR
« Reply #167 on: 12/14/2020 02:41 am »
Not sure if this has been covered, but this thread seems a good place for it:

https://www.fnc.co.uk/discover-frazer-nash/news/frazer-nash-exploring-viability-of-space-based-solar-power-to-help-deliver-net-zero

The UK Government is looking for risky ventures, perhaps to try and compensate for the Brexit damage. They have now commissioned a study into Space Solar Power.

This is relevant to SpaceX because if the cost of launching a solar power station is less than the cost of building the solar arrays, then it might be possible to make a business case for it.

Launch cost = System Weight x Cost per unit mass
Quote
As part of the study, we are looking at the leading three SBSP concepts, from the USA (SPS Alpha), UK (CASSIOPeiA) and China (MR-SPS). SBSP experts John Mankins (USA) and Ian Cash (UK) – the inventors of the first two concepts – are supporting our study.

Problem with using SBSP en-masse is and always has been MMOD.

Micrometeoroid impacts blast away ~100x as much mass as the original impactor, and SBSP offers a huge target (you almost couldn't design something worse for MMOD unless you launch buckets of sand or something). So even if you dodge the big chunks, your solar panels will slowly get "eroded away" by untrackable MMOD. Since each impact multiplies the amount of tiny debris, you don't need too many SBSP installations before you're substantially increasing the MMOD environment in your chosen orbit.

Note that while the Kessler syndrome runaway threshold depends only on the total mass in a certain orbit, a large area satellites will be eroded away into fragments faster than a compact satellite.
Nope, not at all. SBSP occurs in GSO, and the tiny dust produced gets pushed away via solar pressure.

We've had solar-powered satellites in GSO for over half a century. SBSP is probably a bad idea, but not for the reason you posited.
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Re: Space Solar Power with BFR
« Reply #168 on: 12/27/2020 04:09 pm »
Yang et al. 2016 presents a 2 GW, 23,000 t GEO SSP concept: SSPS-OMEGA (Space Solar Power Station via Orb-shape Membrane Energy Gathering Array).

They highlight the principal advantage of GEO over LEO:  "simple attitude control".

Does it make sense to scale SSP to 23,000 t, just to simplify attitude control?

Refs.

Yang, Y., Zhang, Y., Duan, B., Wang, D. and Li, X., 2016. A novel design project for space solar power station (SSPS-OMEGA). Acta Astronautica, 121, pp.51-58.
« Last Edit: 12/27/2020 04:27 pm by LMT »

Offline mandrewa

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Re: Space Solar Power with BFR
« Reply #169 on: 01/05/2021 02:25 pm »
Caltech Space Solar Power Project

Thanks to Jansen for making me aware of this.

I skimmed this entire thread and I find no mention of it.  I skimmed the Advanced Concepts/Solar Power Satellite thread and TrevorMonty did post a link to it.  But the discussion following that was so brief that I wonder how many people actually looked at it.

But the point is this may be happening.  The Caltech team has done some amazing work. 

Here's the link to the project website: https://www.spacesolar.caltech.edu/

Here's an hour long presentation of the idea:

Here's a brief four minute video looking at the 'tile' which is the modular element that is the heart of this proposed solar power satellite:

And a small demo is going to be launched on SpaceX's third transporter mission at the end of 2021.  See https://www.satellitetoday.com/launch/2020/12/15/momentus-lands-caltech-mission-for-its-new-hosted-payload-service/
« Last Edit: 01/05/2021 02:27 pm by mandrewa »

Offline mandrewa

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Re: Space Solar Power with BFR
« Reply #170 on: 01/05/2021 03:14 pm »
At 34:55 into the video (Space Solar Power: A New Beginning - Sergio Pellegrino - 10/31/2018) is the slide:
"Levelized Cost of Electricity (LCOE) GEO vs. MEO"

This assumes a fifteen year operational lifetime for a solar power satellite that has been
launched on the Atlas V 551.

If the weight of the basic solar power satellite element can be brought down to 0.16 kg/m2
then the electricity from a solar power satellite in GEO should cost about $2.06 per kilowatt-hour
or $1.77 per kilowatt-hour if it comes from five solar power satellites equally spaced around
the earth at MEO.

Now that's a higher number than you see on your electric bill.  But there are three things to
remember here.  First this is a baby-in-the-bathwater situation.  Assuming there isn't
something fundamentally wrong with this cost estimate, these numbers will only get better
with time.  And second, maybe it would be more appropriate to compare to the cost of
electricity produced by solar cells on the earth instead of in general, and although that's
going to be a controversial subject, so much so that I wonder if I should go there, but still
it may be that looked at from that perspective that this is a genuinely economically
competitive idea even at the baby-in-the-bathwater stage.

And third, of course, what does it do to the cost estimate if instead of launching on the
Atlas V 551 it is launched on Starship?
« Last Edit: 01/05/2021 03:15 pm by mandrewa »

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Re: Space Solar Power with BFR
« Reply #171 on: 01/05/2021 06:14 pm »
At 34:55 into the video (Space Solar Power: A New Beginning - Sergio Pellegrino - 10/31/2018) is the slide:
"Levelized Cost of Electricity (LCOE) GEO vs. MEO"

This assumes a fifteen year operational lifetime for a solar power satellite that has been
launched on the Atlas V 551.

If the weight of the basic solar power satellite element can be brought down to 0.16 kg/m2
then the electricity from a solar power satellite in GEO should cost about $2.06 per kilowatt-hour
or $1.77 per kilowatt-hour if it comes from five solar power satellites equally spaced around
the earth at MEO.

Now that's a higher number than you see on your electric bill.  But there are three things to
remember here.  First this is a baby-in-the-bathwater situation.  Assuming there isn't
something fundamentally wrong with this cost estimate, these numbers will only get better
with time.  And second, maybe it would be more appropriate to compare to the cost of
electricity produced by solar cells on the earth instead of in general, and although that's
going to be a controversial subject, so much so that I wonder if I should go there, but still
it may be that looked at from that perspective that this is a genuinely economically
competitive idea even at the baby-in-the-bathwater stage.

And third, of course, what does it do to the cost estimate if instead of launching on the
Atlas V 551 it is launched on Starship?
$1.77 is cheap for forward military base that needs to truck generator fuel through hostile territory. This is likely to be first application followed by remote mining operations and likes of Antarctic base.

Can also be used to supply lunar base through lunar night. Laser maybe better option for power beaming here as receiver is lot smaller eg solar panel.

Great thing about these satellites is they can beam their power to most parts of world during an orbit.

Sent from my SM-G570Y using Tapatalk


Offline mandrewa

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Re: Space Solar Power with BFR
« Reply #172 on: 01/05/2021 06:55 pm »
At 32:50 into the video is a slide breaking down the energy flow and efficiencies of the
proposed solar satellite at GEO:

The assembled satellite is basically a 730 meter by 730 meter square. There are 730 megawatts
of solar radiation passing through the square at all times. The solar cells intercept 25% of
that energy, and produce 182.5 MW.  Half of that energy is lost during the conversion to the
microwaves, that brings us down to 91.25 MW.  Five percent that energy is effectively lost
during its steerable emission (it's a phased array antenna) towards the receiving array on earth.
Now it's down to 86.7 MW.  And finally 19% of the energy is not received and converted into
electricity by the receiving antenna.  So that brings it down to 70 megawatts that have
appeared in useable form at the antenna on the earth.

So multiplying that gives an overall efficiency of 9.6%.

This may sound low, but what matters is that you get 70 megawatts at your receiving attenna
non-stop. 

So you take that 70 megawatts and you assume it's good for at least 15 years and then divide
that by the total cost of the whole system, including the launch costs, and that, basically, is
where the cost per kilowatt-hour figure ($2.02 per kilowatt-hour for GEO with the Atlas V launching
the system) comes from.

Offline Robotbeat

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Re: Space Solar Power with BFR
« Reply #173 on: 01/05/2021 07:35 pm »
85 tons in GSO, roughly. Atlas V551 does 3904kg to GSO. $150m per 551 (optimistically) puts that at 22 Atlas V launches for $3.3 billion. 9.2 TWh for 70MW over 15 years. But only 36¢/kWh. Falcon Heavy might cost about the same per launch but get, I dunno, maybe 3x the payload. 12¢/kWh.

One starship and 4 tanker flights should be plenty. If $2million per launch (SpaceX says maybe $1 million marginal cost, so let’s be generous), that’s $10million. Or about 0.1¢/kWh in launch costs. If that’s $20 million per launch, still only 1¢/kWh.

Out of $2/kWh.

Launch costs basically already don’t matter. It’s all hardware costs now for space based solar power.

A hobbled together space solar power satellite with cheap Chinese cells and an array of microwave oven magnetrons tricked into being in phase would be cheaper than the hyper-mass-optimized approach taken here.

Another consequence of Starship: that 85 tons can be launched in one go (using refueling), so if you get deployment right, you don’t need in orbit assembly.
« Last Edit: 01/05/2021 07:38 pm by Robotbeat »
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

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Offline wes_wilson

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Re: Space Solar Power with BFR
« Reply #174 on: 01/05/2021 08:49 pm »
It's always felt to me that space solar power makes as much or more sense at Mars than here.   Those pesky deployment questions are solved, power made available across large areas of the planet, support for smaller, mobile, and more remote activities.   Long distance transmission lines never needed.  etc


@SpaceX "When can I buy my ticket to Mars?"

Offline mandrewa

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Re: Space Solar Power with BFR
« Reply #175 on: 01/06/2021 05:26 pm »
So checking your calculations, Robotbeat, I get:

(730 MW)(0.25)(0.5)(0.95)(0.81) = 70.217 MW
(70.217 MW)(24 hr)(356)(15) = 8,999,000,000 kWh = 9.0 TWh

And then I was looking again at the slide at 32:50 into the "Space Solar Power: A
New Beginning - Sergio Pellegrino - 10/31/2018" video and realized that I had
missed something.  There is another factor, I'll call it the "main lobe factor" until
I have a better name, that reduces the power and efficiency.  So adding that, I get:

(730 MW)(0.25)(0.5)(0.95)(0.81)(0.84) = 58.982 MW
(58.982 MW)(24 hr)(356)(15) = 7,559,000,000 kWh = 7.56 TWh over a 15-year lifetime.

The number of Atlas V launches required to put a solar power satellite in geosynchronous
orbit depends on the mass of the solar power satellite.  The 'tiles' that they are
currently making mass 0.6 kg/m2. They hope to significantly reduce that mass.  But
meanwhile they don't know how much they will be able to reduce it.  So they show the
cost as a table with different lines for different masses.

But that table implies, if we make a reasonable assumption, that most of the cost
of the solar power satellite is in the launches.

My assumption is that the final mass of the 'tile' after they go through a significant
learning curve will be set by physics.  And that the cost to manufacture a tile will
be whatever it is and it's basically independent of the mass.

Sergio circled 0.16 kg/m2, which is one-quarter of their current mass, during his
presentation, and I assume that means he thinks they will be able to do that.

But I doubt they made the assumption that the final cost of a 0.16 kg/m2 tile is
going to be four times more expensive than what a 0.6 kg/m2 tile would have been.

So I assume they are assuming some cost to manufacture a tile which is based
on what it currently costs them to manufacture a tile, except that as Sergio explains
later, they are hoping that they will be able to cut that cost in half as they
make more and more of these tiles, and that this cost will stay basically the same,
regardless of the final mass.

Now if that is how they are modeling this, then looking at the "Levelized Cost of
Electricity GEO vs. MEO" slide at 34:56 in the video, gives a cost per kilowatt-hour
of $4.18/kWh for 64 launches to GEO versus $2.06/kWh for 19 launches to GEO.

Those two data points, using a simple linear model, imply a fixed cost of $1.165/kWh,
or $8.8 billion in total.  And this includes the cost of making the solar power satellite
plus all other fixed costs.  And then there is a variable component that depends on the
number of launches needed to put the satellite in orbit.  These numbers and assumptions
imply a cost of $356 million per launch.  And that does not include the cost of the
payload.

So if it takes 64 launches, that's $8.8 billion plus $22.8 billion, or $31.6 billion.
Dividing that by 7.56 TWh gives $4.18/kWh. Check.

Or if it takes 19 launches, that's $8.8 billion plus $6.8 billion, or $15.6 billion.
Dividing that by 7.56 TWh gives $2.06/kWh. Check.

Now it would be so much easier, if I actually knew how they were doing their cost
model. But I think this is a reasonable assumption.

The only problem is that $356 million per launch of the Atlas V 511 seems pretty high.
Historically it seems kind of okay, but I'm pretty sure that ULA has lowered its price.

Possibly Sergio and company are sandbagging this.

But if we assume that the Starship will charge $10 million per launch five years from
now, and if it takes five launches to get this solar power satellite to geosynchronous orbit,
then that would give us $8.8 billion plus $0.05 billion, or $1.17/kWh.

Note that this is not the cost to the consumer.  This is what it costs to make that
energy.

But Starlink definitely changes the equation. We go from an environment where most of
the cost is in the launching to one where the path to making energy cheaper is to lower
the cost of manufacturing the satellite itself.
« Last Edit: 01/06/2021 05:30 pm by mandrewa »

Offline LMT

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Re: Space Solar Power with BFR
« Reply #176 on: 01/06/2021 07:01 pm »
Near-field GEO SSP would require km-scale transmitters, due to fraunhofer distance limit.  Arc second beam precision is also required, and this unaddressed challenge is especially great because it's comparable to building a km-scale satellite microwave telescope.  Gavan and Tapuchi 2010 characterizes a (single) 127 m transmitter of this type as "a colossal task to achieve".  The transmitter described in the Caltech video would be over 40x that "colossal-task" area, and what's worse, it would be composed of some 150 independent transmitters whose beams must be coordinated down to the arc second. 

Rectenna scale is a second problem disfavoring GEO SSP.  Of course, the presented Caltech system would function more efficiently in VLEO, and the 2021 test is in LEO.

Refs.

Gavan, J. and Tapuchi, S., 2010. Microwave wireless-power transmission to high-altitude-platform systems. The Radio Science Bulletin, 334, pp.25-42.
« Last Edit: 01/06/2021 07:06 pm by LMT »

Offline mandrewa

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Re: Space Solar Power with BFR
« Reply #177 on: 01/06/2021 08:46 pm »
LMT, I've tried to download the paper you cited but every time that I do that I get
an error message about a third of the way through the download. So I have not been
able to read it.

But from what I understand of the post you linked to, this fraunhofer distance limit
is the point at which the microwave beam would to start to spread out, and that before
that limit the microwave beam stays together, kind of like a laser.  So that as long as
you stay within the fraunhofer distance limit a high efficiency in the transmission
of microwave energy can be achieved.  Hence, this is a considerable part of the reason
you are advocating for solar power satellites in VLEO.

Now that's a fascinating and counterintuitive fact but it doesn't mean that Caltech's
proposal would not work.  It just means that a higher percentage of the energy would be
lost in going from GEO to the surface than would be the case for VLEO to the surface.

That higher loss is already in the Caltech proposal.  They have taken that all into
account as far as I can see.

You are correct that the receiving antenna for a microwave beam coming from GEO has
to be large.  It would be a whole field of short dipole antennas spread out over a
disk 1.5 kilometers in diameter, or 640 acres.  And I believe that area can be simultaneously
used for something else, like for instance a farm, but maybe not.

And the emitting antenna (in GEO) is almost as large.  It's a square 750 meters on a side,
or 139 acres.

I'm sure you know the emitting antenna in the Caltech proposal is part of their 'tile.' It
is not a separate structure.  And that this 'tile' simultaneously turns solar radiation into
electricity, transforms that electricity into microwaves, and then acts as a phased array
antenna that can shift the direction of the microwave beam extremely rapidly and can even
emulate the simultaneous transmission of energy to multiple receiving antennas on the
surface of the earth at the same time.

I suspect this extremely rapid response time is why the Caltech team thinks they
can aim multiple phased array antennas at a target on earth and consistently hit it with
all of them.  And intuitively it seems to me, although I don't really know, that as long
as they have rapid feedback, so they know when they are hitting their target or not, that
they should be able to do this.

But regardless of my understanding, there is no hint in this hour long presentation by
Sergio Pellegrino that this is a issue.

Now I'm not deprecating the idea you are proposing.  They are two different things.  But
if you are saying that the Caltech proposal will not work, I'm not understanding why.
« Last Edit: 01/06/2021 08:51 pm by mandrewa »

Offline LMT

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Re: Space Solar Power with BFR
« Reply #178 on: 01/07/2021 02:17 pm »
I suspect this extremely rapid response time is why the Caltech team thinks they
can aim multiple phased array antennas at a target on earth and consistently hit it with
all of them.  And intuitively it seems to me, although I don't really know, that as long
as they have rapid feedback, so they know when they are hitting their target or not, that
they should be able to do this.

I think it's foremost a challenge of precision beam forming at km scale, using independent transmitters, to meet near-field arc second requirement.  Caltech hw hasn't addressed that challenge. 

Gavan and Tapuchi know microwave transmission very well.  I think their judgment of the "colossal" problem carries weight until some new hw demonstrates precision at km scale: e.g., a km array on Earth that beams a useful fraction of its energy to a GEO rectenna.
« Last Edit: 01/07/2021 02:37 pm by LMT »

 

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