THE idea of collecting solar energy in space and beaming it to Earth has been around for at least 70 years. In "Reason", a short story by Isaac Asimov that was published in 1941, a space station transmits energy collected from the sun to various planets using microwave beams. The advantage of intercepting sunlight in space, instead of letting it find its own way through the atmosphere, is that so much gets absorbed by the air. By converting it to the right frequency first (one of the so-called windows in the atmosphere, in which little energy is absorbed) a space-based collector could, enthusiasts claim, yield on average five times as much power as one located on the ground.
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