Quote from: aero on 05/01/2018 04:06 pmQuote from: whitelancer64 on 05/01/2018 03:50 pmQuote from: alexterrell on 05/01/2018 03:18 pmQuote from: whitelancer64 on 05/01/2018 03:08 pmYou'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.
Quote from: whitelancer64 on 05/01/2018 03:50 pmQuote from: alexterrell on 05/01/2018 03:18 pmQuote from: whitelancer64 on 05/01/2018 03:08 pmYou'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?
Quote from: alexterrell on 05/01/2018 03:18 pmQuote from: whitelancer64 on 05/01/2018 03:08 pmYou'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.
Quote from: whitelancer64 on 05/01/2018 03:08 pmYou'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.
You've completely ignored Elon Musk's point: conversion and transmission losses. That's the number one problem with beamed space based solar power.
Quote from: aero on 05/01/2018 04:06 pmQuote from: whitelancer64 on 05/01/2018 03:50 pmQuote from: alexterrell on 05/01/2018 03:18 pmQuote from: whitelancer64 on 05/01/2018 03:08 pmYou'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.
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?
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.
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.
Quote from: Elmar Moelzer on 05/01/2018 01:42 pmI 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). ...
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.
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!
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.
Quote from: alexterrell on 05/01/2018 02:00 pmQuote from: Elmar Moelzer on 05/01/2018 01:42 pmI 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.
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!Quote from: rickyramjet on 05/01/2018 07:37 pmOn 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!
Quote from: LM13 on 05/01/2018 02:31 pmI'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.