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Space-based solar energy

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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