Solar Sale

A tiny, cost-effective solar cell nearly doubles the amount of electricity generated by sunlight as compared with standard photovoltaic cells. Developed by Spectrolab (a company that makes solar cells for spacecraft) with funding from the Department of Energy, the so-called multiple-junction solar cell consists of germanium and several layers of gallium arsenide. Each layer responds to different wavelengths and works with sunlight concentrated by lenses or mirrors, thereby maximizing the conversion efficiency.

Percent of conversion efficiency in: Standard silicon cell: 12 to 22

Spectrolab cell: 40.7

Number of layers in Spectrolab cell: 20 to 30

Size of cell in square centimeters: 0.26685

Maximum concentrated solar input in watts per square centimeter: 24

Equivalent concentration, number of suns: 240

Electrical output in watts: 2.6

Estimated cost in cents per kilowatt-hour: 8 to 10

SOURCES: Department of Energy Announcement, December 5, 2006; Spectrolab