Air Force Perspective on Present and Future Space Power Generation

Photovoltaics continue to be the primary source for electric power for space missions. The need for ever higher power, specific power, areal power density, and radiation resistance continues to push development of novel solar cell technologies. To meet present and future space power requirements, conventional crystalline multijunction solar cells, next generation thin-film solar cells, and novel technologies are being pursued. In the near to mid term, III-V based multijunction solar cell efficiencies are being increased through incorporation of new materials and metamorphic structures. These efforts are expected to result in AM0 solar cell efficiencies of 33-35%. For thin-film solar cells, significant progress has been made in moving to lightweight polymer substrates and incorporation of monolithic integration, pushing cell level specific powers over 1800 W/kg. Efficiencies continue to increase through better process control and post process treatments. Incorporation of new materials and tandem structures promises to further increase thin-film solar cell efficiencies. For the longer term, novel material systems and nanotechnologies are being investigated. Examples are InGaN alloys which show promise for a continuously varied bandgap with composition, and intermediate bandgap or nanostructured solar cells which take advantage of size dependant light absorption to absorb more of the solar spectrum. To take advantage of new technologies, novel module and array structures are also being developed