Space-based solar energy

Written by adam


Generating solar energy in space stations and beaming it down to earth is a wacky idea, but it’s also an interesting one, and not just for the obvious reasons (outer space, energy beams, etc). To explain why, I need to make a digression into some energy facts and figures.

Solar energy enthusiasts are fond of pointing out that enough energy from the sun hits the earth every hour to fill humanity’s needs for a full year. This is meant to sound very impressive, but really it’s cause for at least a little bit of concern.

In the long term, the amount of solar energy reaching the earth’s surface represents the maximum amount of energy available to humankind. If we flip around the statistic about the amount of energy that reaches the earth in an hour, we see that the sun is sending us roughly 8,000 times the amount of energy we presently consume.

That seems like a lot! But how much of it can we actually make use of? Only 30% of the earth is covered in land. And let’s say that, through dedicated effort, we’re able to cover 5% of our land with solar panels. And maybe those solar panels covert 20% of the light that hits them into electricity. Of course, things aren’t static on the demand side. By 2050, the earth will contain 50% more people. And those people will be much wealthier than they are today, so they might use, on average, double the amount of energy we do now.

Multiply this all through, and the sun is only sending us 8 times the amount of energy we need to keep the human population fat and happy. That still gives us some headroom, but not a lot. And this analysis fails to take into account that electricity usually needs to be produced close to where it’s consumed, so the pressures on land use in densely populated areas could be enormous.

A recent article in the New York Times comes at the issue from the opposite direction, estimating the area needed for energy production based on the energy density of various types of renewable power technologies. It’s an interesting and readable article, so go read it, but the punchline is roughly similar to my analysis above:

>For illustration, imagine getting one-third of that energy from wind, one-third from desert solar power and one-third from nuclear power…

> If a country with the size and population of Britain — 61 million people — adopted that mix, the land area occupied by wind farms would be nearly 10 percent of the country, or roughly the size of Wales. The area occupied by desert solar power stations — in the case of Britain, they would have to be connected by long-distance power lines — would be five times the size of London. The 50 nuclear power stations required would occupy a more modest 50 square kilometers.

> The effort required for a plan like that is very large, but imaginable. Countries that claim to be serious about creating an alternative energy future need to choose a plan, stop arguing and get building.

The assumptions underlying both analyses may be significantly off, but the basic message is sound: powering ourselves with renewable energy is doable, but it’s also a really big undertaking that will push against some tricky constraints. (Related message: energy efficiency is really, really important.)

Space-based solar energy may help to sidestep some of these land-use constraints. Such schemes, of course, face their own daunting engineering challenges, but one can imagine a far future in which such exotic forms of power generation become an important part of the mix. Recently a California company signed a contract with PG&E to deliver space-based power by 2016. And Japan just announced an initiative to build a 1-gigawatt plant in space by the 2030s.

Much more on the benefits and challenges of the technology is available here. The inevitable Joe Romm takedown of the idea is here. I suppose I should add the obligatory caveat that most highly speculative, far-off technologies don’t pan out. In other words: you’ll be waiting a long time for that jetpack.

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  1. Rob Morris

    I love this idea, although at the same time I cautiously contemplate the alternative uses of space-beamed energy as a weapons platform; then, I suppose this is a problem faced by all energy technologies.

  2. Ben Ide

    …Multiply this all through, and the sun is only sending us 8 times the amount of energy we need to keep the human population fat and happy.
    I might have done my math wrong, but I got 12 times the amount needed to maintain our future lifestyle. And this, of course, is with today’s technology.
    And wouldn’t we actually only need 1X?

  3. Adam Stein

    Hm. I did it again and still get 8. The thing that takes it from 12 to 8 is the 50% population increase (6 billion to 9 billion). I’ve edited the post to make that more clear.
    You do only need a factor of 1, assuming that a) my figures are exactly right and b) no future growth. Neither are very good assumptions, and the amount of headroom gives a sense of how wrong they can be before we hit fundamental limits. Of course, the assumptions can be wrong in either directions — maybe we really have much more headroom than this. On quick and dirty analysis, though, it doesn’t appear that we’re swimming in excess energy. Splashing around in it, maybe.

  4. Rob Morris

    Ben, let’s not forget that the actual implementation and maintenance cost of such a large alternative energy infrastructure will consume a significant, or at least noticeable, portion of the energy gained, leaving less to splash around in. All the more important, then, to start creating that infrastructure while we have access to higher yield non-renewable energy.
    In the swimming pool analogy, I suppose it is a bit like taking into account the amount of water required to make the pool and the amount lost to evaporation until we’re done swimming in it…

  5. richard schumacher

    What does “wacky” mean in this context? “Overly complex and inappropriate”? “Easy to deride”?
    Joe Romm makes a pretty good case that the PG&E deal is a scam, or at least isn’t going to work for several reasons that are valid in the short term. In the long term there’s nothing inherently speculative about the idea. All the necessary technologies exist, even the ability to manufacture carbon-neutral rocket fuel to launch pieces of the systems.
    The military application for space-based power is to provide reliable power to remote locations. It makes a poor weapon because it’s so big, expensive and easy to attack. Any harm it could do would be done far more cheaply and easily with missiles or bombs.
    We need to recognize that eliminating fossil fuels is going to be very expensive, take decades, and in the case of wind and ground-based Solar require thousands of square miles of area for collectors and hundreds of thousands of miles of new transmission lines. Nuclear at least has the advantage of compactness.

  6. Bryan Bushley

    Regardless of the math, this sounds like a very expensive and technically and politically complex undertaking that would take many years to be fully implemented and to pay off, if it ever does. I’m not saying we couldn’t do it, but is it worth it? Wouldn’t it be better to make use of the large amount of space we already have available for solar power (e.g., rooftops!) and focus our creative energies on producing more localized and efficient solar energy panels and more efficient, diversified alternative energy systems all around? I believe that, ultimately, our energy problems will not be solved by a single silver bullet, but by many silver pellets.

  7. Jesse

    Forget the fact that this project is a waste of effort, resources, and brainpower that could be spent more productively: Projects like beaming solar energy from space is why nobody takes alternative energy seriously in the first place. It all sounds too… pie in the sky.

  8. Fred

    I don’t get it – if the project can be shown to be impractical, as you claim, that would constitute a rational argument against it – although there does not seem to be any such argument made so far. But are you saying that independent of rational grounds, a naive person’s immediate uninformed reaction (‘that sounds crazy’) should dictate research and policy? It’s reminiscent of Senator Proxmire and the Golden Fleece awards, if anyone is old enough to remember those – transiently amusing and long-term damaging.

  9. richard schumacher

    Well put.

  10. Adam Nott

    I recently read a good book called
    “The Next Hundred Years”. It was basically a glimpse into geopolitics over the next 100 years. One of the interesting highlights was space based solar… which of course the author predicted would first be used to provide the massive amounts of energy needed by the military. And yes, it came with the militarization of space.

  11. Rob Whiteley

    Ahh yes, the “Militarization of Space”. That’s a shibboleth, and a silly one. Most anything the military can do in space can be done far more cheaply in the air or on the ground. And BTW, the military space budgets are not getting any larger. They’re shrinking in real terms.
    Producing solar arrays in space to generate electricity is an old concept, that has always suffered from one fatal flaw: cost. In the space business, solar arrays cost about 500-1000$ per watt to construct and launch into LEO orbit. These are very high performance multi-junction arrays, admittedly. But even lower quality crystalline silicon arrays will be 300-500$ per watt to build, test, launch, and deploy in orbit on a large scale.
    Now compare that to the installation costs for a solar system on the ground. I just recently got a quote to build a turn-key system for about $5.50 a watt. I politely declined the offer because I can do better. In fact, I think costs in the $3.50 a watt range will become routine in the next few years. Even at the $3.50 per watt cost point, my payback time is still more than 3 years. At $350 a watt, the payback time is ~300 years. Since no solar array in space lasts longer than about 15 years, you can never break even. All of this of course assumes commercial rates for electricity pricing.
    Bottom line: Until the end-to-end system price for on-orbit solar power gets low enough so that the payback time is equal to or less than the panel lifetime, this isn’t remotely economically feasible. That break-even point would be at something like $20 per watt. Right now, we’re a factor of 20 more expensive than this, with no compelling breakthroughs that would close that gap rapidly.

  12. disdaniel

    Rob @11
    Are you counting the fact that you get ~ 10 times more sun in space. Without clouds or night you get sun 24/7 and you get about 1/3% more energy at the limit of the atmosphere than you do on the ground.
    Space could be the “killer-app” for low cost thin film solar.
    I’m not rejecting your conclusion, just your 20x expense factor.

  13. Pio Martinez

    If I remember correctly, this idea was proposed in the seventies, during that energy crisis. It was opposed primarily by environmentalists. The concern was the potential harm to wildlife flying through the transmission beam to the receiving station. Has that concern been solved?

  14. Anonymous

    Has anyone taken into consideration how much of the sun’s beamed energy is used by systems and creatures other than human beings? Why does the phrase “it’s all connected” continually take a back seat to “it’s all about us?” A good portion of that energy is already claimed and in use by our ecosystem.

  15. dlmchale

    hello, in my prior visits to this blog regarding solar I’ve spoken only to the simple cost relationships. We should deliever the simple cost relationships 1st. Again these concepts terra-pass puts forward in these blogs all involve central delievery systems concieved to keep the current energy producers providing ‘all we need’. Local, every roof top energy production used at the source. Less line loss, less new grid expense, less relay stations, less everything. I saw the tv show on this topic. The energy would be sent via microwave and the unseen problems where mind boggling. So lets simply cover the exisiting structures at the demand centers and give us a cash for energy plan like the ‘clunkers’ deal and this will create the: “new world order” of localism.