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Anyone can do their part for the planet - as millions of people did for an hour last month by turning off the lights. The trick is to do it without resorting to darkness.

For the moment, Japan leads the way with its ambitious program to collect solar energy in space, convert it into electromagnetic microwaves and deliver it wirelessly to precise locations on Earth. This transmission technology will do to terrestrial power lines what cellphones did to telephone poles. Funded in part by a consortium of 16 corporations (led by Mitsubishi Electric), Japan expects its prototype space-based power station to provide electricity to 300,000 Tokyo homes by 2030.

In the end, though, the United States won't be far behind - and, for competitive reasons, probably will surpass Japan in the pursuit of space-based solar power. Ostensibly at least, Tokyo lacks the military motivation of Washington - although, as a resources-bereft country, Japan must ensure its energy supply from somewhere else simply to survive.

For its part, the U.S. Defence Department's National Security Space Office (NSSO) adopted space-based energy as a strategic priority in 2007. President Barack Obama's 2010 budget, which essentially cut lunar adventures to fund economy-class spaceships, can be interpreted as a prerequisite investment in space-based energy: A power station in space, 36,000 kilometres or more above Earth, will require 120 launches (of maintenance crews) a year.

With its unclassified assessment of space-based solar power, the NSSO remains an accessible source of information on the relevant science and technology. For a bureaucratic organization in a military hierarchy, the NSSO compiled its report in a uniquely collaborative way - at no cost. The agency simply created an access-controlled website and invited the world's leading scientists to participate - and 170 did. The NSSO report reflects the scientific consensus.

The strategic prize, the NSSO concludes, is obvious: Space-based satellites can economically tap "an inexhaustible strategic reservoir" of clean, renewable energy by 2050 or earlier.

The military importance, it notes, is also obvious: "For the [Department of Defence]specifically, beamed energy from space … has the potential to be a disruptive game-changer on the battlefield." With wireless technology, space-based solar power could deliver electricity across an entire theatre of war - right down to the individual soldier. It could dramatically reduce the chance of international conflict arising from energy shortages, and it could provide on-demand energy for humanitarian purposes in disaster zones. In short, the NSSO says, it could enable the U.S. military "to remain relevant" for the 21st century.

"The basic idea is very straightforward," the NSSO says. "Place very large solar arrays into an intensely sunlit Earth orbit. Collect gigawatts of electrical energy and electromagnetically beam them to Earth." The electricity could be delivered to either conventional electrical grids or directly to consumers. It could also be used to manufacture synthetic hydrocarbons.

Spread an array of solar collectors over a single square kilometre, the NSSO says, and you can collect a supply of energy - every year - "equal to the energy contained in all of the known recoverable conventional oil reserves on Earth today."

This amount of energy "indicates that there is enormous [energy]potential for … the nations who construct and possess an SBSP capability." One of the countries that has expressed its interest in acquiring such a capability, the NSSO says, is Canada.

Although complicated, the delivery of space-based energy would not be much more heroic than "the construction of a large modern aircraft carrier, a skyscraper or a large hydroelectric dam." A single solar-power satellite would be 15 times the size of the International Space Station (344 metric tonnes). In comparison, the Great Pyramid at Giza has a mass of 5.9 million metric tons.

Although the space beam would require a sizable target on Earth, this receiver would be based in a desert - perhaps in South Dakota or sub-Saharan Africa. With its abundant supply of energy, though, these desert zones would be transformed into lush agricultural land. (The NSSO compares the intensity of the space beam to the heat thrown off by a campfire.)

The NSSO expresses considerable curiosity why environmentalists appear obsessed with much more difficult terrestrial energy sources that can't be as efficiently or as cleanly produced as space-based power - which, it says, would produce (on a "lifecycle" basis) one-60th of the carbon emitted by fossil fuels.

You would think that environmentalists would be thrilled to join forces with the Pentagon. As Thomas Edison put it in 1931: "I'd put my money on the sun and on solar energy."