In many ways, space is the perfect place for a solar energy array. There are no clouds in the way, no seasonal variability, no atmospheric filtering, and your solar panels can operate at peak efficiency around the clock, since the planet doesn't block the Sun. Put a solar panel in space, according to some estimates, and it'll generate 6-8 times more energy than it can down here on Earth.

Getting the power back down to the surface? Now there's the problem. Geosynchronous orbit, in which a satellite stays more or less right above a single point on the Earth, is about 36,000 km (22,500 miles) up in the air. That's nearly three times the width of the Earth, and a bit further than most extension leads can reach. Transmission, plus the hideous expense of space launches, has been the problem.

But space launch costs are coming down with the advent of reusable rockets and alternative launch technologies, and the world is in desperate need of reliable clean energy, so research on space solar continues, particularly focused on improving the efficiency of wireless power transmission, in the hope that we're just a couple of breakthroughs away from commercially competitive extra-terrestrial power generation.