Author Topic: Space-based solar power for Earth  (Read 189348 times)

Offline Robotbeat

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Re: Space-based solar power for Earth
« Reply #500 on: 05/14/2016 01:03 am »
The simplest space-based power is, of course, PV. I recently discussed with the facilities manager of a major UK industrial player the (it seemed) no-brainer approach of putting PV onto the roof areas of their production buildings, only to discover that they were *very* wary of the prospect of high power DC gubbins in their roofspace. No worries about PV as a source, big worries about anything which wasn't a commodity and which could set fire to their roof/kill staff.

Microwave is full of the same issues. Put the rectenna farms somewhere harmless, and sell the power onward!
Install them on microinverters, then you have AC power, same as everything else in the building.
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Offline A_M_Swallow

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Re: Space-based solar power for Earth
« Reply #501 on: 05/14/2016 01:04 am »
The simplest space-based power is, of course, PV. I recently discussed with the facilities manager of a major UK industrial player the (it seemed) no-brainer approach of putting PV onto the roof areas of their production buildings, only to discover that they were *very* wary of the prospect of high power DC gubbins in their roofspace. No worries about PV as a source, big worries about anything which wasn't a commodity and which could set fire to their roof/kill staff.

Microwave is full of the same issues. Put the rectenna farms somewhere harmless, and sell the power onward!

Any major reason why PV on their roof would be different from PV on house roofs?

Offline SICA Design

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Re: Space-based solar power for Earth
« Reply #502 on: 05/14/2016 04:34 pm »
5) operate in an atmospheric window
I'll only refer to microwave transmission through the 1-10GHz atmospheric window.

Quote
Yeah, klystron looks nice, but it's not high enough frequency.
Quote
And for the transmitter, we ideally want even higher efficiency (95%? 98%? Higher?) mainly to avoid needing huge radiators.
Quote
2.45GHz is not what I meant for high frequency. That's 12cm wavelength. We really want more like cm wavelength, so 30GHz. Otherwise the antennae are just way too big.

For a latitude of 30deg (Houston, Tx: 29.76deg) and 30GHz, the atmosphere will absorb up to 45% (2.6dB loss) of the microwave power (see the bold line in the graph). This gets rapidly worse for higher frequencies.

At 45deg latitude (Minnesota: 46.73deg), 30GHz absorption is up to 68% (5dB loss), compared with 4.5% at 2.45GHz.

There is a reason why virtually all technically sound SBSP concepts use either 2.45GHz or 5.8GHz for transmission to a ground rectenna.

You are concerned with the size of the transmitter, but make no mention of the size of the solar collector, which for a 1GW-to-grid system would need to intercept ~12GW of sunlight (see NG/Caltech or other loss chain references). At Earth's distance from the sun, the irradiance is ~1370W/m^2, requiring 8.76E6 m^2 of collector area - equivalent to a 3.3km diameter disc.

I've pointed out that a system which uses the same substrate for both PV and microwave phased array is not only 11 times less massive (compared with the 1978 reference), but requires no active cooling system (29 times less dissipation density) and can be constructed using very low-cost silicon CMOS - technology which was not capable in 1978. [edit:] Increasing the transmitter diameter from 1km to 3.3km (without mass penalty) reduces the required rectenna size by the same proportion (all else unchanged).

My only main issue with the NG/Caltech proposal is that it appears to be in the wrong orbit if it wants to avoid cosine loss due to effective microwave aperture.

The HESPeruS concept avoids this issue by operating in a Molniya orbit, avoiding the need for any rotating parts (which all constant power GSO-based SPS systems require).
« Last Edit: 05/16/2016 07:30 am by SICA Design »

Offline Bob Shaw

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Re: Space-based solar power for Earth
« Reply #503 on: 05/15/2016 10:38 am »

Microwave is full of the same issues. Put the rectenna farms somewhere harmless, and sell the power onward!

Any major reason why PV on their roof would be different from PV on house roofs?

They are incredibly risk averse - as simple as that. Homeowners are blessed with breezy ignorance, and their insurance providers are blessed with a deep knowledge of statistics. People in big businesses will stick with the status quo as long as possible.

Offline Robotbeat

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Re: Space-based solar power for Earth
« Reply #504 on: 05/15/2016 01:14 pm »

Microwave is full of the same issues. Put the rectenna farms somewhere harmless, and sell the power onward!

Any major reason why PV on their roof would be different from PV on house roofs?

They are incredibly risk averse - as simple as that. Homeowners are blessed with breezy ignorance, and their insurance providers are blessed with a deep knowledge of statistics. People in big businesses will stick with the status quo as long as possible.
The incredibly risk averse do not survive long in a truly competitive environment.
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 SICA Design

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Re: Space-based solar power for Earth
« Reply #505 on: 06/08/2016 04:14 pm »
On the other hand, the co-operative managed to put ahalf a megawatt of PV on the CIS Tower

And that 575.5 kW of PV capacity manages to generate an average of just 20 kW (according to https://en.wikipedia.org/wiki/CIS_Tower), which just confirms the low utilisation (3.5% in this case) of terrestrial PV in non-optimal locations such as rain-soaked Manchester, UK.

Space-based solar power from GSO could approach 100% utilisation (few hours off-line per-year during equinox period).

Can we bring this discussion back to the thread title?
« Last Edit: 06/08/2016 04:17 pm by SICA Design »

Offline Robotbeat

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Re: Space-based solar power for Earth
« Reply #506 on: 06/08/2016 04:57 pm »
...
Space-based solar power from GSO could approach 100% utilisation (few hours off-line per-year during equinox period)....
...except you MIGHT get about 25-50% of that power all the way to the ground and on the grid. And the cost of the solar arrays will be a small fraction of the total cost.
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 SICA Design

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Re: Space-based solar power for Earth
« Reply #507 on: 06/08/2016 09:03 pm »
...
Space-based solar power from GSO could approach 100% utilisation (few hours off-line per-year during equinox period)....
...except you MIGHT get about 25-50% of that power all the way to the ground and on the grid. And the cost of the solar arrays will be a small fraction of the total cost.

Yes, 50% efficiency DC (space) to DC (grid) is the widely accepted figure.

My viewpoint is based on what technologies can feasibly replace fossil fuels for a sustainable future.
 
Given that land area is a limited resource required (amongst other necessities) for food production, there are few options which can be scaled sufficiently (current 18 TW average, 30 TW by 2040) - and all are subject to political considerations.

Examples to meet near-future 30 TW requirement from each source alone (mixed sources are inevitable):

 ::) Nuclear fusion - awaiting net power demonstration - 3000 x 1 GW plants required (baseload power)
 ::) Nuclear fission having >1% burnup (e.g. molten salt / thorium) - 444 existing (1% burnup) plants, 2556 required (baseload power)
 ::) Space-based solar power - 60W/m^2 based on safe-level peak beam intensity (one-third equatorial sunlight intensity) - dual use (rectenna/agriculture)possible - 5 million hectares required (baseload power)
 ::) Terrestrial solar farm - 10W/m^2 - 30 million hectares required, plus grid-scale storage
 ::) Off-shore wind - 3W/m^2 - 100 million hectares required, plus grid-scale storage
 ::) On-shore wind - 2W/m^2 - 150 million hectares required, plus grid-scale storage
 ::) Bioethanol - 0.2W/m^2 - 1.5 billion hectares required

Current world total agricultural land use is 5 billion hectares https://en.wikipedia.org/wiki/Agricultural_land

Credit to David MacKay (1967-2016) - https://www.withouthotair.com/


Offline Robotbeat

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Re: Space-based solar power for Earth
« Reply #508 on: 06/08/2016 09:12 pm »
...
Space-based solar power from GSO could approach 100% utilisation (few hours off-line per-year during equinox period)....
...except you MIGHT get about 25-50% of that power all the way to the ground and on the grid. And the cost of the solar arrays will be a small fraction of the total cost.

Yes, 50% efficiency DC (space) to DC (grid) is the widely accepted figure.

My viewpoint is based on what technologies can feasibly replace fossil fuels for a sustainable future.
 
Given that land area is a limited resource required (amongst other necessities) for food production...
...stop. We /decide/ to use the land for food production. It's not required. Change in Western diet could dramatically change that. So could and so does technological innovation. For instance, algae is much higher theoretical efficiency than food crops (and can be fed to animals as well, if we decide not to change our diet). And heck, just plain increases in agricultural efficiency means we're farming less land in the US but producing FAR more food than ever.

And the land we /decide/ to use for food in the US vastly outweighs the amount of land needed to totally replace all electricity (or even all energy) with that from solar farms. Heck, just a fraction of the land the US uses for ETHANOL PRODUCTION ALONE would be enough for all our electrical needs supplied by solar.

...and the land ideally suited for solar is not land you can farm anyway (desert).

The land area vs power idea is wrong.
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Offline Robotbeat

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Re: Space-based solar power for Earth
« Reply #509 on: 06/08/2016 09:22 pm »
...
Terrestrial solar farm - 10W/m^2 - 30 million hectares required, plus grid-scale storage...
::) 10W/m^2 is not at all the best that you can do. Maybe relevant for old cells and poor fill factor in northern Europe, but not relevant to most of the world's population.

30% efficiency, 90% fill factor, you can do over five times that in the desert, which is the best place to put solar farms and which doesn't compete with just about anything for land use. Even so, that'd require about 0.1% of the Earth's surface.

Additionally, that power figure is too high as it assumes heating value of fossil fuels, which is a bad assumption for heating and for vehicles because heat pumps and electrical devices are better by about a factor of 3-5.
« Last Edit: 06/08/2016 09:22 pm by Robotbeat »
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

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Offline SICA Design

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Re: Space-based solar power for Earth
« Reply #510 on: 06/08/2016 10:09 pm »
...
Terrestrial solar farm - 10W/m^2 - 30 million hectares required, plus grid-scale storage...
::) 10W/m^2 is not at all the best that you can do. Maybe relevant for old cells and poor fill factor in northern Europe, but not relevant to most of the world's population.

30% efficiency, 90% fill factor, you can do over five times that in the desert, which is the best place to put solar farms and which doesn't compete with just about anything for land use. Even so, that'd require about 0.1% of the Earth's surface.

You may be right to dispute that 10W/m^2 figure:

Worlds largest complete PV solar farm is Topaz in the US https://en.wikipedia.org/wiki/Topaz_Solar_Farm

Nameplate capacity: 550 MW
Site area: 25 km^2
Annual generation, 2015: 1,301,337 MWh = 148.5 MW average
Utilisation: 27%

==> 6W/m^2

Similarly, the "Desert Sunlight Solar Farm" (US) https://en.wikipedia.org/wiki/Desert_Sunlight_Solar_Farm

Nameplate capacity: 550 MW
Site area: 16 km^2
Annual generation, 2015: 613,941 MWh = 70.0 MW average
Utilisation: 12.7%

==> 4.4W/m^2

And - Huanghe Hydropower Golmud Solar Park (China) https://en.wikipedia.org/wiki/Huanghe_Hydropower_Golmud_Solar_Park

Nameplate capacity: 200 MW
Site area: 5.64 km^2
Annual generation (2015?): 317,000 MWh = 36.2 MW average
Utilisation: 18.1%

==> 6.4W/m^2

Quote
Additionally, that power figure is too high as it assumes heating value of fossil fuels, which is a bad assumption for heating and for vehicles because heat pumps and electrical devices are better by about a factor of 3-5.

I agree heat pumps are a sound method for heating. 18TW is a recent actual total world consumption figure - do you expect this to decrease, remain the same, or increase by 2040?
« Last Edit: 06/08/2016 10:26 pm by SICA Design »

Offline a_langwich

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Re: Space-based solar power for Earth
« Reply #511 on: 06/08/2016 11:00 pm »
If you are comparing current technology, let's get some real numbers.  What's the best microwave rectenna transmission efficiency at megawatt or greater power levels right now?  What distance is involved?  How does its efficiency actually scale with distance (ie, including side lobes or other non-idealities)? 

(At a megawatt, you would need 30 million of them to compare to your other energy alternatives that you were listing.  That's not an inconsequential footprint.)

What's the best power transmission efficiency from orbit to earth, ever, and at what power?


Every decades-away, back-of-the-envelope, idealized future technology looks fantastically good when compared to current technology actually built, in full non-idealized reality.
« Last Edit: 06/08/2016 11:02 pm by a_langwich »

Offline Robotbeat

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Re: Space-based solar power for Earth
« Reply #512 on: 06/09/2016 01:39 am »
There are a lot of losses and they stack up. 50% would not be simple to achieve at those distances.
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Offline fatjohn1408

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Re: Space-based solar power for Earth
« Reply #513 on: 06/09/2016 08:44 am »
I worked on a concept at Uni back in the day and my own idea which I still find very attractive is to just put the sats in LEO and have two GEO satellites with individual mirrors per LEO sat. Instead of microwave beaming you use laser to transfer the energy from the LEO sat to the GEO sat to the groundstation on Earth. From LEO to GEO the airy disk (which contains 86% of the energy of the laser beam) only widens to something like 5 meter. If the laser would have a pointing accuracy of an order of magnitude worse than the hubble telescope it would still be very spot on.


Offline Alf Fass

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Re: Space-based solar power for Earth
« Reply #514 on: 06/09/2016 08:52 am »
I worked on a concept at Uni back in the day and my own idea which I still find very attractive is to just put the sats in LEO and have two GEO satellites with individual mirrors per LEO sat. Instead of microwave beaming you use laser to transfer the energy from the LEO sat to the GEO sat to the groundstation on Earth. From LEO to GEO the airy disk (which contains 86% of the energy of the laser beam) only widens to something like 5 meter. If the laser would have a pointing accuracy of an order of magnitude worse than the hubble telescope it would still be very spot on.

Polar Sun synchronous LEO?
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Offline Asteroza

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Re: Space-based solar power for Earth
« Reply #515 on: 06/09/2016 08:55 am »
I worked on a concept at Uni back in the day and my own idea which I still find very attractive is to just put the sats in LEO and have two GEO satellites with individual mirrors per LEO sat. Instead of microwave beaming you use laser to transfer the energy from the LEO sat to the GEO sat to the groundstation on Earth. From LEO to GEO the airy disk (which contains 86% of the energy of the laser beam) only widens to something like 5 meter. If the laser would have a pointing accuracy of an order of magnitude worse than the hubble telescope it would still be very spot on.

Sounds like some Indian SPS (and ground powerplant!) power relay proposals. If you are bothering to use laser beam mirror relay anyways, why not have the low orbit SPS be in terminator riding SSO for continuous sunshine, which would dramatically simplify SPS design (you potentially could do gravity gradient stabilized long rolls of PV with laser beam directors on both ends, maybe embed the fiber laser into the roll)? The relay mirror sats also not necessarily need to be in GEO either, could be in Molniya orbits as well.

Offline SICA Design

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Re: Space-based solar power for Earth
« Reply #516 on: 06/09/2016 10:41 am »
If you are comparing current technology, let's get some real numbers.  What's the best microwave rectenna transmission efficiency at megawatt or greater power levels right now?  What distance is involved?  How does its efficiency actually scale with distance (ie, including side lobes or other non-idealities)? 

(At a megawatt, you would need 30 million of them to compare to your other energy alternatives that you were listing.  That's not an inconsequential footprint.)

What's the best power transmission efficiency from orbit to earth, ever, and at what power?


Every decades-away, back-of-the-envelope, idealized future technology looks fantastically good when compared to current technology actually built, in full non-idealized reality.

Firstly, a cursory read of any major study (going back to the early 70s) will state that SBSP does not scale well below GW levels.

For systems operating in the 1 - 10 GHz atmospheric window (most proposals use either the 2.45 GHz or 5.8 GHz ISM bands), fundamental physics (diffraction optics) dictate the minimum diameters of transmitting antenna and receiving rectenna, to allow focus across 36,000 km (GSO - Earth's surface). For 5.8 GHz and 1.5 km antenna this gives 3 km as the minimum rectenna diameter to intercept 84% of the beam power (the Airy disc).

This is totally independent of power level, which means the first viable Solar Power Satellite (SPS) in GSO has to be full scale - which is one major reason the economics are so high risk.

For a system meeting the diffraction limit, only the last 100 km-or-so affects beaming efficiency, as the beam passes through the atmosphere.

Beaming at low power was demonstrated across 148 km here: http://www.thespacereview.com/article/1210/1

Beaming at 10 kW level across 500m demonstrated here: http://insideevs.com/mitsubishi-wirelessly-sends-electricity-across-500-meter-gap/

For a fully modular retro-directive phased array, each element would be spaced by one half-wavelength (25mm or less guarantees no loss to grating lobes for 5.8 GHz) and would need to efficiently convert dc-microwave at only 100 mW levels.

Other efficiency arguments from a few pages back (click on the link):

50% Efficiency from in-space electrical power to terrestrial grid power is an accepted value (with established precedents) for those working in the field. It is easy to find examples which would not meet this, and no-one is claiming that Space-Based Solar for Earth will be easy.

Unlike terrestrial PV, the real-world environment for the SPS does not involve having to withstand once-in-a-hundred-years weather events (which currently appear to happen more than once per decade) or overcome losses associated with dirt and abrasion. Instead, its challenges are primarily radiation and micrometeorite damage - for which we have a wealth of data gathered from both LEO, MEO and GSO for our existing microwave-beaming earth-observation, comms and GPS satellites.

A fully modular system would not fail catastrophically, but instead be designed for graceful degradation over its operational life.

Offline fatjohn1408

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Re: Space-based solar power for Earth
« Reply #517 on: 06/09/2016 12:05 pm »
I worked on a concept at Uni back in the day and my own idea which I still find very attractive is to just put the sats in LEO and have two GEO satellites with individual mirrors per LEO sat. Instead of microwave beaming you use laser to transfer the energy from the LEO sat to the GEO sat to the groundstation on Earth. From LEO to GEO the airy disk (which contains 86% of the energy of the laser beam) only widens to something like 5 meter. If the laser would have a pointing accuracy of an order of magnitude worse than the hubble telescope it would still be very spot on.

Polar Sun synchronous LEO?

I think that was our proposal if I recall, but I don't know if we made a trade off between the performance capacity of launchers between SSO and LEO. I think our launch costs (assuming the Ariane V at the time) were about 40% of total cost. So if this was launch cost to SSO that means switching to LEO could perhaps maximally save you 20% on costs (assuming SSO capacity is at least half of LEO equatorial capacity) and would probably increase the power output with way more than 20% (no eclipse)

So yes SSO makes the most sense.

What killed the project from being viable in our point of view was the cost of the launchers and the cost of the lasers. But even using the numbers for Ariane VI instead of Ariane V would already make the launch cost drop significantly and that's not even discussing SpaceX, Skylon, Blue Origin etc. Point is launch costs should have been a bit lower than we assumed back then.

The cost of lasers might still be a bottle neck though.
« Last Edit: 06/09/2016 12:11 pm by fatjohn1408 »

Offline fatjohn1408

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Re: Space-based solar power for Earth
« Reply #518 on: 06/09/2016 12:14 pm »
I worked on a concept at Uni back in the day and my own idea which I still find very attractive is to just put the sats in LEO and have two GEO satellites with individual mirrors per LEO sat. Instead of microwave beaming you use laser to transfer the energy from the LEO sat to the GEO sat to the groundstation on Earth. From LEO to GEO the airy disk (which contains 86% of the energy of the laser beam) only widens to something like 5 meter. If the laser would have a pointing accuracy of an order of magnitude worse than the hubble telescope it would still be very spot on.

Polar Sun synchronous LEO?

I think that was our proposal if I recall, but I don't know if we made a trade off between the performance capacity of launchers between SSO and LEO. I think our launch costs (assuming the Ariane V at the time) were about 40% of total cost. So if this was launch cost to SSO that means switching to LEO could perhaps maximally save you 20% on costs (assuming SSO capacity is at least half of LEO equatorial capacity) and would probably increase the power output with way more than 20% (no eclipse)

So yes SSO makes the most sense.

What killed the project from being viable in our point of view was the cost of the launchers and the cost of the lasers. But even using the numbers for Ariane VI instead of Ariane V would already make the launch cost drop significantly and that's not even discussing SpaceX, Skylon, Blue Origin etc. Point is launch costs should have been a bit lower than we assumed back then.

The cost of lasers might still be a bottle neck though.

Other problems were clouds, so we thought the ground stations should be near Phoenix on the one hand (for US) and in in the northern Sahara on the other hand (for Europe/North Africa)

Offline Hanelyp

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Re: Space-based solar power for Earth
« Reply #519 on: 06/09/2016 05:14 pm »
I worked on a concept at Uni back in the day and my own idea which I still find very attractive is to just put the sats in LEO and have two GEO satellites with individual mirrors per LEO sat. Instead of microwave beaming you use laser to transfer the energy from the LEO sat to the GEO sat to the groundstation on Earth. From LEO to GEO the airy disk (which contains 86% of the energy of the laser beam) only widens to something like 5 meter. If the laser would have a pointing accuracy of an order of magnitude worse than the hubble telescope it would still be very spot on.
Lasers are much less efficient than microwave generators.  Photovoltaics, even designed for a single wavelength, can't beat a rectina for efficiency.  Lasers don't deal well with overcast, while microwaves of a well chosen wavelength have little loss through the atmosphere even with heavy clouds.  On the other hand, you can get a much tighter, even dangerous, power beam.

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