A startup is trying to generate power in space for use on Earth–an old idea that’s never been tried, mostly because it’s too expensive, but also because people are concerned that it will fry birds in flight.

One of the biggest long-term challenges with solar power is that it doesn’t work well when it’s cloudy, and it stops working altogether at night. Most proposed solutions have to do with storing energy from the sun, but a more exotic way around this problem, first proposed in the late 1960s, involves putting the solar panels in space where the sun is always shining. The power would then be beamed to Earth in the form of some sort of electromagnetic waves, likely lasers or microwaves, to a ground-based station that could then deliver power to customers over existing transmission lines. The government has spent $80 million over decades to investigate this approach, but so far no pilot plants have been built.

Now Solaren Corporation, a startup based in Manhattan Beach, CA, is trying to get the idea off the ground. It’s working with the California utility Pacific Gas and Electric (PG&E), which intends to enter into a power-purchase agreement with the company. If the agreement is approved by regulators, starting in 2016, the utility will purchase 200 megawatts of power from Solaren at an undisclosed price–that is, if the startup can get a system into space and working by then. The company has already selected a site in California for the receiving station; it hasn’t said exactly where, but it will be close to a PG&E substation and won’t require long-distance transmission lines.

Solaren hasn’t released many details about the system. CEO Gary Spirnak says that it’s conceptually the same as communications satellite technology: it uses solar panels to generate electricity, which gets sent to Earth in the form of radio waves, which are received by antennas on Earth. In a Q & A published by PG&E, he said that the design is “a significant departure from past efforts,” so it will be economically feasible. The first system will reportedly be able to generate 1,000 megawatts–about the size of many conventional power plants. The company will need to raise billions of dollars to construct the plant. Right now, it only has 10 employees.

According to a 2007 report (PDF) from the federal government’s National Security Space Office, space-based solar is now technically feasible as a result of advances in solar cells and robotics for construction, among other things. But the designs that it considered would be far too expensive for providing the sort of general-purpose, base-load power that Solaren intends to sell. Instead, the government office recommended that the first systems be developed to beam power to troops at forward military bases, since the military can afford to pay a premium. Right now, such bases have to pay an order of magnitude more for their electricity than most customers do. The power could also be used to make synthetic fuels to offset diesel and jet fuel that can cost $20 a gallon in a war zone.

Even then, the report was skeptical about the economic success of the first space-based power plants. The rocket launches alone could be a big problem: the report estimated that building just one power plant would require 120 launches, while the United States only launches about 15 a year (as of 2007). “Even with the [Department of Defense] as an anchor tenant customer at a price of $1-2 per kilowatt hour … when considering the risks of implementing a new unproven space technology and other major business risks, the business case for [space-based solar power] still does not appear to be close in 2007 with current capabilities (primarily launch costs),” the report said.

Solaren claims to have addressed these launch costs with its new design. It reportedly can build its first power plant with only four or five launches.

Another common concern is safety. Will beaming down massive amounts of power harm birds or airplanes that cross the path of a beam? Or what if the beam isn’t aimed properly and sends its power into the middle of a city? According to the government report, these concerns are unfounded. In the system that it analyzed, the intensity of the beam would be “approximately [one-sixth] of noon sunlight,” with the power absorbed over a wide array of antennas. “Because the microwave beams are constant and conversion efficiencies are high, they can be beamed at densities substantially lower than that of sunlight and still deliver more energy per area of land usage than terrestrial solar energy,” which by comparison only generates electricity about a quarter of the time, the report said. The intensity would be less than the intensity of microwaves allowed by appliance standards to leak out of microwave ovens, the report claims. [Update: This doesn’t appear to be accurate. If the energy is really one-sixth the energy from the sun, as exaerospaceace points out below, this would be roughly three times the allowable limit for microwaves. But one-sixth the energy from the sun still doesn’t sound too dangerous. Of course, the sun can cause some pretty nasty burns if you stay out in it too long. Best not to stand around under the beam.] If the beam were to wander over a city, the results would be “anticlimactic,” the report said.

But even if Solaren can raise the money it needs and convince people that the system is safe, it could still face opposition from other governments around the world–for example, many governments will be concerned that it could be used as a weapon. “The complexity of negotiating any type of international legal and policy agreements necessary for the development of [space-based solar power] will require significant amounts of time (5-10 years),” the report said.

In the end, because of the many obstacles to the technology, the report recommends that the government build a pilot plant to demonstrate the technology, suggesting that only the government has the resources to make it happen. It says that later, once the technology is proven and costs for launches come down, it might become economically viable. Solaren seems to think that it’s found ways around these problems. It will be interesting to see what they come up with. For now, it’s hard to see the agreement with PG&E as more than clever marketing for the company and the utility.

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