Getting Solar Off the Ground

Power Player / by Lee Billings /

William Maness on why alternative energy and power grids aren’t good playmates and his plans for beaming solar power from space.

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Seed: What about the high cost of launching payloads into orbit? That’s a lot of heavy lifting to do before you turn a profit.
WM: It takes big, expensive rockets to get into low-Earth orbit (LEO), where the space shuttle goes. What most people don’t know is that to get from hundreds of miles up in LEO to 22,000 miles up in geosynchronous orbit (GEO), where a powersat wants to be, only requires about a third as much energy as it took to get to LEO in the first place. That’s doesn’t seem like a big deal until you realize that the propellant for that final leg of the trip has to be launched from Earth. In 2000 I came up with a proprietary idea to make this problem go away; it’s called the “solar-powered orbital transfer,” or SPOT. SPOT uses the solar collectors on the spacecraft to power ion thrusters, which gradually lift the system to GEO. SPOT can reduce the launch mass of an SBSP system by 67 percent. On a 2,500-megawatt system, that’s roughly $1 billion worth of cost savings. So even if our competitors get contracts with utility companies, they still have to come play with us.

The other key proprietary idea we have is called BrightStar. Classical SBSP proposals call for a single huge transmitter to hit a small spot on the Earth, the receiving station. BrightStars are smaller satellites, each one about 1/300th the size of a classical transmitter, guided by a pilot signal from the ground and working together in a phased array to form a beam. So we don’t have to ever build and launch this huge, honking, monolithic antenna—we just send up a cloud of solar satellites.

Seed: How many total satellites do you need for the first big stage of supplying power to utilities?
WM: Our baseline design is a 2,500-megawatt receiving station, which is only about 5 percent of our total costs. That would require about 300 BrightStars weighing 10 tons apiece, or 600 BrightStars at five tons each. We’re talking to several different launch service providers, including SpaceX and Lockheed Martin, but hundreds of launches is daunting. It’s a chicken and egg problem: You don’t have a cheap space access because you don’t really have recurring payloads, and you don’t have recurring payloads because you don’t have cheap space access. PowerSat can change that. We bring to the table credit-worthy customers with billions to spend, the utility companies, and say, “Please build us a way to launch these things efficiently.” If they build it, we will come.

Seed: So what’s the timeline of your plan?
WM: In the next 18 months, we’re aiming to do a 10-kilowatt ground-based wireless power demonstration, followed by a 1-megawatt ground-based demonstration a year after that.

The 10-kilowatt demonstration will only beam power over 300 yards or so and wouldn’t have much commercial purpose. We’ll be scaling up the engineering lessons we learn from that system and porting them to the 1-megawatt demonstration. The next step after the 1-megawatt ground station is launching a single BrightStar. One of these alone can’t form a beam tight enough to do anything useful on the ground, but it can transmit power sufficiently to be measured, and we can demonstrate our solar-powered orbital transfer.

Seed: What are the other big hurdles facing SBSP and PowerSat?
WM: We’ll need to find a suitable site for building the receiver station and get approval for it. From above, the receiver looks like an ellipse roughly a mile wide, between 1.5 to 2 miles long. But it’s not as environmentally disruptive as a terrestrial array of solar cells. Picture something that looks a bit like chicken-wire mesh strung up on utility poles between 30 and 50 feet off the ground. Anything underneath it doesn’t get substantial microwave impingement since the receivers above are catching the energy. If you put one of our receivers up over some pastureland, it can remain pasture. Rain and sunshine go right through it, so it doesn’t have major environmental effects.

The only real disruptive effect is on cell phones or wireless internet communication. Directly beneath the beam, that stuff won’t work, so you don’t want to do this in the middle of an urban area. You’d also want to have a no-fly zone around the receiver, which is already done for other power production facilities.

The bigger problem is, there are only a couple of good windows for microwave transmission in the atmosphere. One’s at 2.45 gigahertz, which is exactly the frequency that cell phones and wireless internet use. Another is at 5.8 gigahertz, which also has a lot of communications sitting on it. Ultimately SBSP has to have a dedicated chunk of the spectrum, which would require dealing with the international body that does frequency allocation on a planetary scale. They’d need to say that power transmission would occur on exactly 2.45 gigahertz or 5.8 gigahertz, with a slot of 5 kilohertz to either side of it. We don’t want to drift from that. If we do, we lose a substantial amount of electricity to heat, which generates a lot of effects we really don’t want to deal with. So this would mean that new cell phones and wireless devices would need a filter built into them that would work around that frequency. The filter wouldn’t be expensive. The problem of frequency allocation is probably the biggest regulatory issue facing us now.

Seed: What’s the toughest part of talking with people about SBSP?
WM: I’ve spent the last eight years of my life fighting the “giggle factor.” When politicians or investors hear about SBSP, they get a little smile on their face, probably thinking about when they saw it in SimCity 2000. It drives me nuts because this isn’t science fiction. Powersats are no more science fiction than satellite television. What this is about is enabling the continued, controlled growth of our society and our standard of living in a way that doesn’t destroy the planet. I don’t want anyone to have to think about where their electricity comes from. But in order to get there, people like me have to think a lot about what happens behind the scenes when the lights get switched on.

Originally published July 28, 2009

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