Solar power from space

California energy utility PG&E has contracted with the private company Solaren to put solar panels in space — and beam the power back to earth. Solaren hopes to start commercial operation by 2016, pulling 200 megawatts from orbit — that’s about half what an average coal fired power plant generates.

John Mankins is an expert in space based solar power. He managed NASA’s space solar power studies before starting his own company, Managed Energy Technologies. On "Living on Earth," he explains how it all works.

Mankins says a solar satellite is no small undertaking: "It’s about a half a mile across for the transmitter and it’s on the order of ten thousand tons or approximately twenty international space stations. It would collect the sunlight and convert it into electromagnetic radiation into a beam of energy and then send it to some other locations such as a receiver on the earth."

If you’re envisioning a giant laser beam of concentrated solar power shooting down to the planet, that’s not quite how it works, says Mankins: "Hopefully, no one would ever actually build such a system. The beam when it’s up in space would start out at about a half a mile across and then it would spread and be on the ground – and again everything depends on the details of the engineering – but it would spread to be approximately four miles across. You’d certainly want to take the right precautions, keep the energy density, the amount of power that’s in a square meter of the beam low enough to be safe. You’d want to geographically isolate the receiver so it wasn’t in a populated area. And you’d want to have safe guards so that planes would, for example, not be allowed normally to fly through the beam and in the event that one did inadvertently or deliberately try to fly through the beam, you’d have to be able to cut it off in a timely way so that – a sort of belt and suspenders and buttons approach – so that it was safe to start with, it’s remote, and you turn it off just in case."

He explains how the energy gets on the surface of the planet: "Very, very elegantly. There’s basically a simple antenna with a diode in the middle of it, and it takes incoming radio waves and converts it at very, very high efficiency, maybe 80% or 85% efficiency into voltage. Mechanically, it would look a great deal like chicken wire, like a mesh, and so even though you had this large antenna collecting energy from the solar power satellite above you, below the ground itself would still receive something like 80 percent of normal sunlight, the rain would pass though, it would not have any kind of significant impact on the sort of the ecosystem, whether it was farms or natural land beneath it."

The solar power is collected on the orbiting satellites, and the solar energy in space is much stronger than it is here on earth: "So up in space the average sunlight passing the earth from the sun is about 1,400 watts per square meter. And on the earth at mid summer, mid day in the desert, it’s about 1,000 watts per square meter. And on the earth, of course, you add the additional factors of normal atmospheric absorption, you add weather, you add nighttime and the overall average sunlight which is available per square meter up in space is significantly greater than that which could ever be collected on the earth."

As for how to position a satellite so that it gets sunlight all the time: "A lot of different cases have been looked at. The one that looks the most promising is to place these solar power satellites in what’s called a geostationary earth orbit — that’s the same orbit that used for example by broadcast satellite radio or by broadcast TV satellites. Its high above the earth, about twenty three thousand miles up, and it has an usual property — that the time it takes for a satellite to go around the earth at this particular distance is just at 24 hours. If you use the right kind of transmission technologies, this is basically solid state arrays, you could deliver power from one satellite to New York in the morning to Dallas at midday and to Los Angeles in the afternoon."

Mankins says it’s going to be worth the investment: "If you can solve the engineering problems, if you can get solar energy from space — for on the order of ten cents a kilowatt-hour, which is highly competitive with terrestrial energy sources — space solar power has the potential to provide absolutely carbon neutral energy to billions of people 24/7. So those would be problems definitely worth addressing."

Hosted by Steve Curwood, "Living on Earth" is an award-winning environmental news program that delves into the leading issues affecting the world we inhabit. More "Living on Earth."