Some questions about space based solar power

Factual Questions
1

Was reading an article today discussing space based solar power systems that would collect energy in orbit then beam the energy back to stations on earth to be converted and put into the power grid. My questions would be…how feasible is this technology? How much would it cost? Is it worth developing from a cost to benefit standpoint? How much loss is there when beaming the power back to earth? When converting the power for use on the grid? What countries COULD develop this technology (assuming it’s feasible)?

-XT

2

My impression is that this isn’t a very realistic power source. The sun already beams energy down to earth, in the form of electromagnetic radiation, something like a horsepower per square yard. I don’t know if harvesting beamed microwaves would be much easier, even if the satellite collector-converter-transmitters were free. Besides, microwaves are considered harmful (notice all the interlocks and shields on your microwave oven). Having very intense ones beamed at the Earth’s surface from thousands of miles away sounds controversial or worse.

Sorry I don’t have any numbers on hand.

3

XT: Don’t know about this subject, but I sent you a private message on a solar question I had earlier today. PM me back if you have any advice. Thanks.

4

From the National Security Space Office (evidently a part of the Dept. of Defense, but accountable to the Director of National Intelligence as well), describing a 2007 “Phase 0” study of space-based solar power (SBSP):

Probably too far from reality to make any meaningful cost estimates, but it won’t be “too cheap to meter”, that’s for sure.

5

Napier, sunlight can only be converted into electricity by solar panels which are currently inefficient, costly, and stop working when the sun goes down. Microwaves can be converted with much higher efficiency, and the satellites would be in geosynchronous orbit, high enough that they would only seldom be in shadow. As for hazardness, it’s envisioned that the earthbound receivers would be in unpopulated areas- desert, mountains or floating platforms at sea. Cost… well, the problem is that the cost is dictated by how expensive it is to launch anything from Earth into orbit. At current prices, an absolute fantasy, and they’ve been promising cheaper spaceflight for decades and it’s stil not here.

Back in the 1970s, it was proposed that the solution would be a stupendous economy of scale by establishing manned colonies (not space stations, colonies) in high orbit, constructed mostly of raw materials harvested from the moon. Once a almost completely self-sustaining industrial infrastructure was established in space, the marginal cost of having the coloinists build power sats would in theory be economical. Google “O’Neil colonies” for more info.

So why did it never happen? AFAIK, the problem was twofold: to even begin the project, you’d need a very economical way of getting stuff into space. In the 70s, they actually believed the hype that the Shuttle would make spaceflight cheap and routine, and that some sort of heavy cargo lifter would be even cheaper. The utter failure of the Shuttle to achieve this meant that we were back at square one.

And secondly, if step one proved to be a hurdle, the sheer ambitiousness of the proposal seemed impossible. Not that it would require fundamentally new technology, but it would requre engineering things nobody has ever bulit, in conditions no one has every tried to work in. It would require establishing a mining colony on the moon, with a linear mass driver to boost millions of tons of raw material to lunar escape velocity; building mammoth (miles across!) structures in free orbit; perfecting 99.9999% perfect recyling of air, water and food; solving innumerable engineering challenges to do all this in hard vacuum, microgravity and huge sun/shade thermal fluctuations. And all the while, all this would have to work. It would be like trying to build the Golden Gate Bridge as the very FIRST time anyone have ever tried to build a steel-cable suspension bridge. If some unknown unforseeable show-stopper brought the whole endeavour to a screeching halt, you would have wasted trillions of dollars. In short, it simply required too big a jump from what we confidently know we can do.

6

>Napier, sunlight can only be converted into electricity by solar panels

No, there are a few other methods. You can focus light on a boiler and run a steam plant. There are several facilities already that work this way, typically with a small tower holding the boiler at the top, and a field of tracking mirrors that each relay a solar image onto the boiler. You can also split water into oxygen and hydrogen. I think the device that does this is a glass or silica tube with some catalyist or something inside, through which water flows, and upon which reflectors focus concentrated sunlight.

7

[QUOTE=Napier]
No, there are a few other methods.
[/QUOTE]
You’re right, I guess I was unconciously thinking of direct-to-electricity. But in any case, the methods you cited also have mediocre conversion efficiency. My original point being that there is a rationale behind gathering the sunlight in space. The no-interruption-at-night is probably the biggest.

8

I have real doubts about space based solar power. Yes, you get 24 hour power, but you are adding a lot of inefficiencies - the energy it takes to get the satellite up in the first place, the conversion losses in converting the solar power into a beam that can be sent back to earth, atmospheric attenuation, and then conversion inefficiencies in converting the power beam back to usable electric power. Plus the cost would be horrendous without a major breakthrough in orbital lift capability.

There are techniques for converting solar power to other forms of energy that can be stored when it’s cloudy/dark. You can use solar to make hydrogen through electrolysis. You can use the electricity to run pumps to fill up water reservoirs, then drain the water through generators at night. You can use solar power to directly heat water or some other liquid, then use heat exhangers later to extract energy. All of these have inefficiencies and losses, but it’s SO much cheaper to do this stuff on Earth that I can’t imagine space-based solar power being able to economically compete with alternatives.

Now, if we got an orbital tether built so we could move these things up into orbit for close to nothing, it’s a whole different ball game.

But really, where I think you’re going to see solar fitting in in the future is not as a primary energy source, but as millions of small secondary energy sources. Give me cheap enough solar power, and I’ll put it on my roof. If I have an electric car, I’ll park it outseide and let it trickle charge from solar during the day. If solar panels get really cheap, you’ll see them everywhere. Street lights will use solar power to charge batteries and only have grid connections for emergencies (you already see this in some places). Solar-powered air conditioning makes a lot of sense, since you need the air conditioning most when the sun is shining. That sort of thing.

Throw some wind into the mix, add nuclear plants for baseline load, maybe some clean coal plants here and there, a bit of carbon sequestration, and there’s your energy grid of the future. All these sources will feed into it when able.

What we really need the most is better battery technology. With better batteries, we can do everything with electricity, and once we can do everything with electricity, we can diversify the power grid and bring new technologies online as they are available without having to rebuild the consumption infrastructure. Better batteries would also allow you to make solar power during the day and store it at night or when it’s cloudy.

9

[QUOTE=Lumpy]
So why did it never happen? AFAIK, the problem was twofold: to even begin the project, you’d need a very economical way of getting stuff into space. In the 70s, they actually believed the hype that the Shuttle would make spaceflight cheap and routine, and that some sort of heavy cargo lifter would be even cheaper. The utter failure of the Shuttle to achieve this meant that we were back at square one.
[/QUOTE]
To be fair, Gerald O’Neill wasn’t relying on technology like the American Space Transportation System (Shuttle) or disposable rockets; he assumed that single state to orbit and nuclear propulsion technology would allow much more cost effective access to space, which would install enough infrastructure to make large space colonies essentially self-sustainable, at least for basic necessities and the industrial base to build power generation, as discussed in [post=6426547]this thread[/post].

Of course, for O’Neill, solar power beamed to Earth wasn’t an end upon itself, but rather a justification for investing in the construction of large space habitats to begin with as a first step toward colonization of space. He hung his hat on this one not because it was technically feasible and economically viable (the question of which still remains, at least on the scale envisioned) but because it was something that could be politically and fiscally viable as an argument. As for the technical side, the beam was to be very broad with low energy density (hence, needing a vast antenna array in the middle of a desert). I suspect climate effects are not fully understood; even absorbing a fraction of a percent of the terawatts of energy that was alleged to be produced in one narrow bandwidth might cause a lot of unforeseen issues. Orbiting solar power is, at this state of the technology, nothing more than a pipe dream.

The Shuttle, while disappointing to say the least, isn’t an “utter failure”; while launch costs are much higher than predicted, this is in part a result of longer turnaround time and less commercial need for heavy lift access to space. When NASAs main external customer from the STS program, the USAF, ditched Blue Shuttle and made best efforts to shift satellite launches to (somewhat) more cost effective disposable launchers, it pretty much undermined the entire program. If STS had the turnaround capability and payload demand to permit one launch per month instead of the max of 3-5 per year that it averaged post-Challenger launch costs would be significantly reduced, perhaps even competitive with commercial heavy lift launchers. The Shuttle was never going to satisfy the kind of payload to orbit needs to building an O’Neill colony, though; that would require something on the scale of Project ORION nuclear pulse propulsion.

[QUOTE=Sam Stone]
What we really need the most is better battery technology. With better batteries, we can do everything with electricity, and once we can do everything with electricity, we can diversify the power grid and bring new technologies online as they are available without having to rebuild the consumption infrastructure. Better batteries would also allow you to make solar power during the day and store it at night or when it’s cloudy.
[/QUOTE]
Better battery technology and a more flexible electricity infrastructure would certainly free us from having to rely on specific modes of power generation, especially remote or vehicular power which essentially mandates some kind of combustion engine. However, power density in batteries and fuel cells is only inching up with no revolutionary breakthroughs in sight.

Better power storage technology would be of significant benefit, but it isn’t the dealbreaker in using solar power in grid-connected applications. There are plenty of other ways to store energy temporarily. The real problems with solar are the footprint required for dedicated solar emplacements (farm), which is restricted by both the power density of sunlight itself and the photovoltaic or thermodynamic efficiency of the conversion process, and the emplacement and maintenance cost per unit power. I doubt that PV will ever be a viable sustainable source, but solar thermal and solar-derived (i.e. wind and wave) power can provide relatively reliable sources of power, if geographically limited. The biggest handicap in implementing solar and solar-derived power sources is uncertainty; the technologies involved have been proven only on modest scales, and the upfront costs are at best barely competitive with conventional fossil fuel.

As carbon fuels become more scarce, solar may become more appealing, but like Sam Stone, I don’t think it is completely sustainable, certainly not on a global scale and especially for the energy demands of emerging industrial nations like China. More intelligent use of carbon fuels, plus nuclear fission (with its unfortunate wastes and issues) will have to be part of any rational plan for future energy needs, although with development and maturity solar and solar-derived can take on an increasing share of the load. Ultimately, practical nuclear fusion power would solve the supply problem (though the issue of portable energy sources still remains), but even an optimistic outlook tempered by pragmatism suggests that it’ll be four or five decades at the earliest before it would be ready for commercial power production.

Stranger

10

I thought the main problem with space based power is the cost of hauling panels to orbit, the useable lifetime of the panels, and the cost of maintenance and replacement.

But, people who work out what it costs always neglect to factor in how many billions and probably trillions of dollars we spend subsidizing oil & nuclear.

11

[QUOTE=Stranger On A Train]
The Shuttle, while disappointing to say the least, isn’t an “utter failure”; while launch costs are much higher than predicted, this is in part a result of longer turnaround time and less commercial need for heavy lift access to space. When NASAs main external customer from the STS program, the USAF, ditched Blue Shuttle and made best efforts to shift satellite launches to (somewhat) more cost effective disposable launchers, it pretty much undermined the entire program. If STS had the turnaround capability and payload demand to permit one launch per month instead of the max of 3-5 per year that it averaged post-Challenger launch costs would be significantly reduced, perhaps even competitive with commercial heavy lift launchers. The Shuttle was never going to satisfy the kind of payload to orbit needs to building an O’Neill colony, though; that would require something on the scale of Project ORION nuclear pulse propulsion.Stranger
[/QUOTE]
Well, the Shuttle is an utter failure at being cheap and reliable, to the point that it’s going to be scrapped and replaced with what amounts to Apollo/Saturn#II. The turnaround time is what sank the system; they tried for decades to get it down and never did. And the USAF had to ditch the Shuttle, precisely because of the reliability problem. In short, you can’t really say “if it had worked” because it didn’t and no one could make it work. The sad truth is that not everything that can be built can be made practical.

As far as it’s relevence to the powersat/colony proposal, I had read that the baseline for the studies was a shuttle-derived heavy cargo lifter, consisting of the central fuel tank, shuttle engines and avionics packaged in a recovery pod, and four solid rocket boosters. Cheap enough (by 1975 estimates of cost and performance) to get the ball rolling. In other words, if the Shuttle had worked, the O’Neill proposals would have started from standing launch capacity, not requiring a brand new heavy launch system.

12

[QUOTE=Lumpy]
Well, the Shuttle is an utter failure at being cheap and reliable, to the point that it’s going to be scrapped and replaced with what amounts to Apollo/Saturn#II. The turnaround time is what sank the system; they tried for decades to get it down and never did. And the USAF had to ditch the Shuttle, precisely because of the reliability problem. In short, you can’t really say “if it had worked” because it didn’t and no one could make it work. The sad truth is that not everything that can be built can be made practical.
[/quote]
The actual performance and reliability of the STS is within the technical estimates provided by designers; that it did not meet the claims of non-technical advocates and program managers is a result of overpromotion, not a failure to correctly assess the capabilities of the system. The STS was also originally envisioned as an evolving design with major changes occuring with successive fleet articles; instead, the Shuttle fleet was cut back by Reagan, and the design essentially largely frozen. Of the several planned upgrades (including fiber wound composite SRBs needed for Blue Shuttle polar orbit launches, the Advanced Light Weight External Tank, several proposals for replacement thermal protection tiles) the only major upgrades were the upgraded RS-24 SSME, the glass cockpit, and the AP-101S avionics computers. Many of the system evolutions that would have increased payload capacity or simplified refurbishment operations were eschewed because of capital development costs that were outside of budget allocations.

[QUOTE=Lumpy]
As far as it’s relevence to the powersat/colony proposal, I had read that the baseline for the studies was a shuttle-derived heavy cargo lifter, consisting of the central fuel tank, shuttle engines and avionics packaged in a recovery pod, and four solid rocket boosters. Cheap enough (by 1975 estimates of cost and performance) to get the ball rolling. In other words, if the Shuttle had worked, the O’Neill proposals would have started from standing launch capacity, not requiring a brand new heavy launch system.
[/QUOTE]
O’Neill’s baseline for building the colonies were based upon costs for space access that were well below anything even proposed for the STS or Shuttle-derived hardware, on close order of $100/lb access to geostationary or beyond orbit. The Shuttle was never intended to support anything like the large scale habitats envisioned by O’Neill, period.

Stranger