Sunday, July 27, 2008

Solar Power Satellites

The basic idea of solar power satellites (SPS) has been around since 1968, but with high and rising energy costs and with improvements in solar photovoltaic technology, the idea seems to be getting more attention now. There was an opinion piece in the New York Times last week that outlined the basic ideas of SPS, noting that the required technologies all exist now, and that with lighter and higher efficiency solar cells, the mass of an SPS could be much less than the monster systems envisioned in the seventies. The ISS could be used for testing some SPS technologies in space (even though it is in low Earth orbit and therefore doesn't stay over one point on Earth as a real SPS would presumably do from GEO). There are other promising developments:
  • An October 2007 report to the National Security Space Office called "Space-Based Solar Power As an Opportunity for Strategic Security" (available here). Strange maybe, but at least DoD is an interested party with money!

  • Japan has been testing SPS technology including power-beaming and plans to have an SPS in space by 2030 (JAXA concept picture shown).

  • A new organization called SSAFE (Space Solar Alliance for Energy Future) was announced last fall by NSS. SSAFE is a coalition of 13 research and space advocacy groups advocating investments in space-based solar power. NSS also has an extensive on-line library of books and other materials on space based solar power.
A recent article in Air & Space Magazine also talks about the issues of space-based solar power. While there is great promise, and progress is being made, there are also many problems, including public perception of the safety of beaming power to Earth with microwaves (really not a major issue) and the fact that ground-based energy technologies are also developing faster now, reducing possible energy cost advantages of space-based solar. But in the long run, placing arrays of efficient solar cells in a place where the sun always shines is too good an idea to waste!


ZZ said...

Wouldn't the receivers for this also have to be very large?

FlyingSinger said...

Yes, receivers would cover quite large areas (I saw one figure of 6 x 8 miles), which is probably why the Japanese propose to have theirs off-shore (Japan doesn't have much open land area). Other studies have assumed they would be in isolated land areas. The actual size would depend on the size of the transmitting antenna, the wavelength(s) used, the distance from the SPS to the rectenna array (the SPS would be in GEO over the equator but could be aimed to off-equator points within some limits), and other factors. The size would also depend on the allowed energy density of the transmitting beam, which would be set to make it safe for wildlife and humans who wandered into the beam.

So yes, large, but not impractically so.

ZZ said...

So wouldn't jut building a 6X8 mile solar array on the ground result in getting the same energy? Does the atmosphere attenuate it that much?

rberger said...

Its a weapon system, not an energy system if you tune it just so slightly differently. Why do you think the Military is interested?

And even if it wasn't its a boondoggle. We can get renewable energy much cheaper and MUCH more reliably with purely terrestrial systems..

FlyingSinger said...

The orbiting solar cells are in full sunlight 24/7 whereas any solar array on the ground generates no power at night and is affected also by clouds etc. The microwave conversion and coupling efficiency is expected to be very high because they can choose whatever wavelength they want and design the transmitting and receiving antennas to work very well (shape the beam etc.) at the design wavelength.

Anything can be a weapon, of course, so it would be safest to not develop any technology, just stay in the cave except when you have to go out and gather nuts and berries. But the stated reason for military interest is that they have to get electric power to their bases and personnel potentially anywhere in the world, so beaming the power in from space offers some real advantages. And it has a lot of civilian carryover, unlike many military developments (but like some others, such as GPS and DARPA's internet, which I find to be pretty handy).

rberger said...

So if the Military was to use it to power their bases and such, an enemy just has to launch a bunch of rocks into the orbital path of the energy beaming stations and knock out the entire US Military bases that use that power.

Or the same if they are used for the energy source for a country's civilian power.

Its super vulnerable, and there are many other terrestrial technologies that are distributed and cheaper. The alternatives aren't Space Based power or living in caves.

FlyingSinger said...

OK, sorry - you're right, the alternatives are not space based power or caves. I am totally in favor of developing ground-based alternative energy, solar, wind, geothermal, tidal, etc. as well as expanded nuclear power and research into fusion (even if it's always 20-50 years in the future). But for some circumstances, space based solar may have real benefits, and it's worth doing some initial development, as the Japanese are clearly doing. With small land area and high technology, it may be just the thing for them. There doesn't have to be one solution, and just because the military is interested in it doesn't mean it's a Death Ray.

Big Al said...

When I first heard about this concept, I thought it was nutty. It's actually a good idea. you could start with power for island nations and go from there.
It would however require the development of a million pound booster rocket to orbit the materials.

Eric M. Collins said...

rberger: As mentioned, just about any beneficial scientific or technological advance can be perverted into a weapon. However, a well engineered system would not only be very robust and reliable, it could also be made to be inherently safe. In this case, the design of the transmitting antenna could easily be made such that it would be impossible to produce a beam that could have sufficient energy density to do any damage.

Also, a satellite in geostationary orbit is a LONG way off, much further than can be reached by all but a handful of rockets currently in existence.

Bruce: Something you said got me to thinking about the wisdom of using this technology to power forward military bases and troops on the ground. Assuming that the power beam is going to saturate a pretty large area by the time it reaches the ground, what's to stop your enemies from tapping into the same energy source?