Solar power from space: moving beyond science fiction

Studies showed that it was a feasible, but daunting, proposition. “This was in the days before PCs, microelectronics, robotics,” says Mankins. “The idea of something like the shuttle’s robotic arm was unimaginable. So you’d need these big crews to bolt the things together - and the satellites themselves would have had to be physically enormous. We’d need a new launch system that would dwarf the space shuttle.”

The bottom line, he says, was that it could be done, but it would have cost the equivalent of a trillion of today’s dollars to get the first kilowatt of power, and it would have taken 20 years. “The National Research Council and the Office of Technology Assessment looked at it,” recalled Mankins. “One of them said, ‘Let’s revisit this in ten years.’ The other said, ‘Let’s never consider this again.’”

In the mid-1990s, NASA did revisit the concept. Under Mankins’ direction, a team of engineers was assembled to see whether advances in technology made space-based solar power more feasible. “The basic answer,” he says, “was ‘yes’”.

In the past decade two other factors have emerged to boost the prospects of SBSP: climate change and interest from the military.

There is a growing recognition that non-carbon energy sources will be crucial if the world is going to avoid the worst effects of climate change. It’s almost inevitable that carbon emissions will end up being taxed one way or another, and when they are, renewables like SBSP will immediately become more competitive economically.

That’s what motivates Solaren and PG&E. Although it is cloaking its work in secrecy, Solaren has said it will cost roughly US$2 billion to launch a handful of satellites carrying the equipment that will be robotically assembled into a single, large solar station. One way the company plans to boost efficiency is to use parabolic reflectors to concentrate sunlight onto the solar cells.

“The biggest expense,” says Cal Boerman, Solaren’s director of energy services, “is the cost of getting into space, and we’re convinced we can get the weight down to the point where we can do this with a minimum number of launches”.

As with any SBSP system, the energy will be converted into microwaves and beamed down to a so-called rectenna - an antenna that “rectifies” the microwaves back into electricity. Solaren’s, to be located near Fresno, Calif., will consist of an array of smaller antennas that will cover about a square kilometre - far less real estate than you’d need if you were using ground-based solar cells to gather an equivalent amount of power.

Because Solaren’s satellite will be in geostationary orbit, the antennas won’t have to track it across the sky; like a satellite TV receiver, they’ll always aim at a fixed point in the sky. At 22,000 miles up, a geostationary satellite is in full sunlight virtually all the time.

As for safety, he says, the fact that the microwaves are spread out over a square kilometre means that they’d be relatively harmless to, say, a flock of birds that happened to fly through them. And if the beam should wander, the satellite will be programmed to scatter it.

Solaren isn’t the only company trying to commercialise SBSP: PowerSat, based in Everett, Wash., has recently filed patents for its own space-power system, which will use an array of hundreds of small satellites linked together rather than one large one. PowerSat says it can reduce some of the high costs of putting the technology in space by using solar energy to power electronic thrusters to manoeuvre the satellites into orbit. A Swiss company, Space Energy, is also working on SBSP. Solaren is the only one, though, with a contract with a utility. “As we talked to investors,” says Boerman, “they naturally asked, ‘Can you sell it?’”

If this first project works out, Solaren eventually wants to put in orbit satellites that can generate a gigawatt of electricity, enough to power roughly 1 million homes.