This Space Power idea is getting a real work out lately. Japan's space agency JAXA has announced it wants to collect solar power in space and zap it down to Earth, using laser beams or microwaves by 2030.
The Japanese government has just picked a group of companies and a team of researchers tasked with turning the ambitious, multi-billion-dollar dream of unlimited clean energy into reality in coming decades.
With few energy resources of its own and heavily reliant on oil imports, Japan has long been a leader in solar and other renewable energies and this year set ambitious greenhouse gas reduction targets.
But Japan's boldest plan to date is the Space Solar Power System (SSPS), in which arrays of photovoltaic panels several square miles in size would hover in geostationary orbit outside the Earth's atmosphere.
"Since solar power is a clean and inexhaustible energy source, we believe that this system will be able to help solve the problems of energy shortage and global warming," researchers at Mitsubishi Heavy Industries, one of the project participants, wrote in a report.
The solar cells would capture the solar energy, which is at least five times stronger in space than on Earth, and beam it down to the ground through clusters of lasers or microwaves.
Several space power announcements have been made by various companies within the last year but none have proved that the basic technology even exist. Sure spacecraft and communications satellites have been powered by solar cells since the start of the space race but the largest space based solar array built to date, on the International Space Station, generates only 120 Kw and it's construction required more than 10 Shuttle launches.
The Japanese researchers are targeting a 1 GW (gigawatt) system, equivalent to a medium-sized atomic power plant, or in the region of 8000 times the size of the ISS array, a fairly ambitious target considering the Japanese haven't even managed manned space flight yet.
The Japanese say the satellite would produce electricity at eight cents per kilowatt-hour, six times cheaper than its current cost in Japan. No details are provided on how that price was calculated.
The power would be collected by gigantic parabolic antennae, likely to be located in restricted areas at sea or on dam reservoirs, said Tadashige Takiya, a spokesman at the Japan Aerospace Exploration Agency (JAXA).
The major show stopper for all these space based solar power proposals is that wireless power transmission has not been proven at any distance over 1 mile yet transmission of power from geostationary orbit must be energy efficient over 22,000 miles! Japanese researchers are also considering laser power transmission but laser signals are almost completely blocked by cloud cover and again this technology is untested for long distance power transmission.
Radio and Laser signals suffer from free-space path loss, which is proportional to the square of the distance between the transmitter and receiver and is also proportional to the square of the frequency of the radio signal.
A radio signal 'spreads out' when it leaves the antenna according to Inverse-square law and as much as possible has to be captured by the antenna aperture at the receiving end to achieve high efficiency. Any energy that spreads out and does not make it to the receiving antenna is considered a loss of efficiency.
Wireless power experiments to date have tired to get around these limits by using extremely focused antenna such as parabolic dishes and co-phased arrays at very close range but they still have yet to deal with loss due to distance as all such successful tests have only been over a mile or less.
Where a conventional long distance high voltage power transmission line is around 95% energy efficient, long distance wireless power transmission would be a small fraction of 1% efficient.
The challenge -- including transporting the components to space -- may appear gigantic, but Japan has been pursuing the project since 1998, with some 130 researchers studying it under JAXA's oversight.
Last month Japan's Economy and Trade Ministry and the Science Ministry took another step toward making the project a reality, by selecting several Japanese high-tech giants as participants in the project.
The consortium, named the Institute for Unmanned Space Experiment Free Flyer, also includes Mitsubishi Electric, NEC, Fujitsu and Sharp.
The project's roadmap outlined several steps that would need to be taken before a full-blown launch in 2030.
Within several years, "a satellite designed to test the transmission by microwave should be put into low orbit with a Japanese rocket," said Tatsuhito Fujita, one of the JAXA researchers heading the project.
The next step, expected around 2020, would be to launch and test a large flexible photovoltaic structure with 10 megawatt power capacity, to be followed by a 250 megawatt prototype.
This would help evaluate the project's financial viability, say officials. The final aim is to produce electricity cheap enough to compete with other alternative energy sources.
JAXA says the transmission technology would be safe but concedes it would have to convince the public, which may harbour images of laser beams shooting down from the sky, roasting birds or slicing up aircraft in mid-air.
According to a 2004 study by JAXA, the words 'laser' and 'microwave' caused the most concern among the 1,000 people questioned.
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