Solar panels in orbit could generate round-the-clock green energy and beam it down to Earth. Has the time for this epic feat of engineering come round at last?

A global contest is under way to tap the sun’s energy from orbit Essy May

PG&E, one of the world’s biggest utilities, has an unusual deal on its books. It has pledged to buy all the solar power produced by a tiny, secretive California start-up. But you won’t find these panels laid out in orderly rows across a baking desert – they will be in orbit 36,000 kilometres above Earth. There, they will collect the sun’s limitless energy and beam it down to power grids.

This isn’t just California dreaming. A surprising number of space solar projects are under way around the world, with some heavyweight backers. China is in on the act, and aims to have prototypes in orbit in the 2020s. Russia has already built a prototype, and Japan is so committed to the idea that it has launched a national space solar programme and plans to have operational satellites by the 2030s. The US Navy and several aerospace firms are interested too. So are we seeing the start of a second space race?

It’s not hard to see the appeal. In space, solar power overcomes three obstacles that frustrate terrestrial producers. There are the obvious issues of night and clouds, but also a less discussed problem. Namely, even on the clearest, longest, brightest day, the atmosphere scatters and absorbs the sun’s incoming energy until only a fraction of its original strength remains. “How much it’s reduced depends on your location,” says Paul Jaffe, who is working on space solar modules at the US Naval Research Laboratory in Washington DC. Once through the atmosphere, the power intensity can be anywhere between three and 20 …