IF IT happens, it will be the space engineering feat that tops them all. Spanning several square kilometres, a space power station would be by far the largest orbiting structure ever built.
While the engineering may be on a colossal scale, the idea behind space solar power is simple enough. Lob giant solar panels into geostationary orbit, then use the electricity they generate to send an intense beam of laser light or microwaves down to Earth where it will be converted back into electricity to be pumped into the grid. In one fell swoop we could slash CO2 emissions and reduce our reliance on oil. The beam could be used to deliver power to remote locations without the need for expensive transmission lines, and even provide instant on-demand electricity to soldiers in the field.
The dream of generating our electricity in space has been around for decades, but so far it has always proved too expensive to follow through.
If the mammoth project could be made to work, the benefits are clear. Put a solar panel out beyond the Earth's atmosphere and it can generate almost 20 times as much electricity as it could on average at ground level, as it would not suffer losses due to atmospheric absorption, day-night cycles and cloud cover.
When NASA and the US Department of Energy took a look at space-based solar power in the 1970s, they concluded it was technically feasible, but the cost ruled it out. A lot has changed since then and three key developments could bring down the size and cost of a solar power satellite. First, solar cells are now four times as efficient at converting solar energy to electricity, beaming technology has improved, solid-state devices can now be used to point microwave beams, so small, easily assembled antennas could be used in place of the kilometre-high monolith originally called for. Finally, robots are now capable enough to do much of the construction work.
Last year a team from Kobe University, Tokyo, sent a rocket up to an altitude of 210 kilometres to deploy a 130-square-metre net - essentially a spiderweb made of wire - connecting a microwave transmitter to two robots that could autonomously move around the web. The idea was that eventually hundreds of these robots would be deployed, equipped with solar panels, to self-assemble and beam power back to Earth. The experiment was a success, but full results have yet to be published.
A recent study led by Yutaro Kobayashi at USEF estimated that the CO2 footprint of a space solar power plant over its lifetime would be about the same per kilowatt-hour of electricity generated as that of a nuclear plant. With climate change rising up the political agenda, it is this sort of environmental advantage, together with concerns for energy security and rising oil prices, that is helping to spur a resurgence of space solar power.
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