Toward space solar power: Wireless energy transmission experiments past, present and future

Solar power is a reality. Today, increasing numbers of photovoltaic and other solar-powered installations are in service around the world and in space. These uses range from the primary electric power source for satellites, remote site scientific experiments and villages in developing countries to augmenting the commercial electric grid and providing partial power for individual businesses and homeowners in developed countries. In space, electricity generated by photovoltaic conversion of solar energy is the mainstay of power for low Earth and geostationary satellite constellations. Still, for all its acceptance as a benign and environmentally friendly energy source, terrestrial solar power has yet to be seriously considered a viable technology for providing base electrical generating capacity. The obvious reason is sunshine on Earth is too unreliable. In addition to the diurnal and seasonal cycles, inclement weather reduces the average daily period and intensity of insolation. However, the Sun shines constantly in space. The challenge is to harvest and transmit the energy from space to Earth. The concept of space solar power based on microwave wireless energy transmission was first put forth more than 25 years ago by Dr. Peter Glaser. We review historical experiments in wireless energy transmission which have brought the technology from a laboratory curiosity to its present status. Results from recent experiments and their implications for wireless energy transmission as an enabling technology for space solar power are reviewed. Current developments are discussed along with proposed terrestrial and space experiments.