Week of December 7

We are currently engrossed in an alternative energy project having little to do with alternative fuels and we have had to cut back on our coverage as a consequence. Thus we are doing only one story for this week.

This has to do with reportage surfacing in the Wall Street Journal on a solar energy proposal which is "on the table" so far as the Obama Administration is concerned, one having to do with placing solar generators in orbit around the earth.

The reporter writing the piece affected a degree of incredulity, and not surprisingly, given the editorial position of the paper, but did quote sources in the scientific community amenable to the notion while seeming to indicate that this is a fairly novel idea.

In fact the notion of placing solar generators in space isn't new at all and goes back several decades. In the intense and unremitting sunlight of interplanetary space photovoltaic generators would output far more electrical energy than their counterparts on earth, and they would not be vulnerable to wind or accumulations of grit. There is a problem in transmitting the energy back to earth, however. A tether or space elevator would seem rather farfetched, though it has been proposed, and a fairly lossless transmission could be realized by the use of a highly focused microwave transmission. A geostationary satellite would be the best platform for transmitting energy in this manner since, for safety reasons, one would wish it to fall upon a single receiver located in a remote area, and thus a stationary transmitter would be almost de rigeur.

I have seen a number of learned papers on the subject from the past, and I was aware of a consortium of investors who were trying to launch a project and who apparently never succeeded. As I say, it's not a new idea.

Solar energy generators are in fact used in satellites today and microwave transmissions emanating from such satellites are routine, though they are utilized for transmitting information, not power. So is extending the notion to encompass electrical generation feasible in fact?

The chief difficulty in executing such a scheme would be in modulating the power output of the solar array to achieve megawatt power beams in the microwave regions. With current technology that would entail the use of hundreds of extremely expensive thyratron gas tubes for transmission purposes, and even then switching these tubes at gigahertz frequencies on a continuous basis would be a major challenge.

Switching solid state devices at even a hundred watts power output in the microwave region is difficult, and achieving outputs in the megawatts is quite impossible, and probably always will be. Vacuum tubes are much better—that's why they're still used in microwave ovens—but I've never heard of multi-megawatt or giga-watt microwave transmissions, and I can claim some expertise in this area since I cover the microwave industry fairly extensively on an ongoing basis. Thyratrons have been made that are capable of nanosecond rise times at multi-megawatt ouptus, what is required for microwave operation, but these tubes are designed for producing brief bursts of extremely high power, not for continuous operation. Using enormous numbers of tubes in parallel for driving a transmitting antenna would appear be the only way to make such a scheme work.

It would be very difficult to estimate the cost of such a project, which would probably involve sending crews aloft to join several acres of solar panels together into a single array. The Iridium satellite telephone project, which involved scores of low earth orbit satellites and represented an undertaking of similar magnitude, ended up costing tens of billions of dollars, but maybe this could be done for less.

But I don't make such caveats to suggest that Obama Administration is foolish in entertaining such concepts. They should be looking at everything because with the current state of technology there are no renewable energy silver bullets. But where they should be putting their money is in readily scalable technologies that can be trialed quickly on a small scale and as quickly assessed for their viability. Orbital solar doesn't appear to meet that criterion.