Energy Biz - September/October 2008 - (Page 96) » technoloGy Frontier Harvesting Solar power in Space JAPAN HAS HigH HOPES By MARTiN ROSENBERg Japan is working hard To advance its laser and microwave research so that solar power generated in space can be beamed to Earth in two decades, Scientific American reported this summer. By 2030, the Japanese hope to generate 1,000 megawatts at an orbiting solar generator and transport it to Earth. To learn more about the effort, EnergyBiz e-mailed questions to Hiroaki Suzuki with the Japan Aerospace Exploration Agency, also known as JAXA. He is one of 180 Japanese scientists working on the program, according to Scientific American. It also reported that the ultimate cost of such a project could climb to tens of billions of dollars, but the Japanese are intent on mastering the technology first, and then driving down the cost to levels that are competitive. Because the orbiting power station would be geostationary it would work around the clock as it is hit with more powerful solar rays than reach the Earth. Hiroaki Suzuki PhOTO anD iLLusTraTiOns cOurTEsy OF Jaxa EnErgyBiz Briefly describe how Japan intends to generate electricity from solar panels in space and then transmit that power to Earth. suzuki We have investigated two types of space solar panel systems, laser and microwave. With laser-based systems, Earth-orbiting solar condenser mirrors concentrate solar energy and divert it to laser amplifiers. A direct solar pumping solid-state laser diode uses the concentrated solar energy to amplify a low-power seed laser beam. The amplified laser beam is transmitted to Earth. Thus, this type of system uses no solar cell panels. Radiators dissipate the laser generator’s waste heat into space. A ground-based photovoltaic device converts the transmitted laser beam into electricity. This system can also be used to produce hydrogen with photocatalytic hydrogen generation or water electrolysis. With microwave-based systems, primary mirrors collect solar energy that solar panels convert to electricity that powers semiconductor devices to generate a microwave beam. A ground-based rectifying antenna array collects the transmitted microwave beam and converts it into electricity that is supplied to commercial power grids. How advanced is the technology? suzuki A current space solar panel system study undertaken by JAXA consists of three main subjects, elemental technology development, ground energy transmission demonstration and concepts and architectures. In the elemental technology development study, a laser amplifier with a direct solar pumping solidstate laser diode made of yttrium aluminum garnet ceramic doped with neodymium and chromium is being studied. The atmospheric transmittal properties of a high-energy laser beam and beam-pointing technology are studied for their applications in a laser-based system. For the microwave-based system, a large-scale phased array antenna, microwave amplifier, retro-directive beam control, and rectifying antenna are being studied. For both systems, a large-scale, ultra-light reflective mirror is also studied. EnErgyBiz September/October 2008 96 E n E rgyB i z
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