The Japanese government is prepared to spend some 2 trillion yen on a one-gigawatt orbiting solar power station—and this week Mitsubishi and other Japanese companies have signed on to boost the effort. Boasting some four kilometers of solar panels—maybe of the superefficient Spectrolab variety but more likely domestically sourced from Mitsubishi or Sharp—the space solar power station would orbit some 36,000 kilometers above Earth and transmit power via microwave or laser beam.

The benefit? Constant solar energy production as the space-based power plant never passes out of sunlight. The downsides? Only enough power for roughly 300,000 Japanese homes at a price tag of $21 billion, according to Japan's science ministry (about 127 million people live in Japan in some 47 million households, according to Wikipedia and the CIA's World Factbook). The Japan Aerospace Exploration Agency (JAXA) aims to have a system in space by 2030.

The first step will be launching a test satellite that will gather solar power and beam it back to Earth, probably in 2015. Already, ground tests show that some solar power (180 watts) can be beamed successfully.

In the U.S., where space solar has been on the drawing board since at least the 1960s, California's Pacific Gas & Electric has pledged to buy power from a planned 200-megawatt space solar station put together by Solaren that is still being developed.

But the U.S. government has mixed feelings about space solar. Despite some $80 million spent over decades by NASA, the alternative energy source is no closer to fruition using public funds. And other government agency estimates put the price tag for space solar at $1 billion per megawatt—making this the most expensive power source identified to date in any solar system.

Image: Artist's rendering courtesy of USEF