(CNN) -- In space there's no atmosphere, it's never cloudy, and in geosynchronous orbits it's never night: a perfect place for a solar power station to harvest uninterrupted power 24 hours a day, 365 days a year. The concept has been around since the 1940s when science fiction writer Isaac Asimov posited the idea of a robot-manned space station that delivered energy to Earth via microwaves. Today, the idea is less science fiction than a steadily advancing reality. Clean energy from above The United States, China, India and Japan all have projects at various stages of development that would see robots assemble solar arrays that could provide the Earth with massive amounts of clean and renewable energy delivered wirelessly. Some variants of the idea could even see as much as 1GW of energy beamed to receivers on Earth -- enough to power a large city. According to Dr Paul Jaffe, spacecraft engineer at the US Naval Research Laboratory, the concept is scientifically sound. "NASA and the US Department of Energy did a study in the late 70s that cost $20 million at the time and looked at it in pretty great depth," Dr Jaffe told CNN. "The conclusion at that time was that there was nothing wrong with the physics but the real question is the economics." The cost lies in the number of space launches required to build the power-transmitting satellite. With costs as high as $40,000 per kilogram for some space launches, the final price-tag for the first space-based solar power station could be as high as $20 billion. Private contractors While the recent entry of private space companies stands significantly to cut costs, basic physics dictates that getting payloads into space is still an expensive undertaking. "The subject is revisited every 10 years when the technology changes and some of the factors affecting the economics change." He said the wars in the Middle East gave new impetus to the space-based solar power as scientific researchers with the military wrestled with the problems of delivering energy to troops in hostile areas. Multiple, and potentially hidden, receivers could tap space-based solar power and relieve the military of the expensive and often dangerous task of supplying troops with generator diesel by either road or air, he said. "If you could deliver electricity from space, that would be kind of attractive," he said. More via CNN.com.