Space-vehicle power requirements have created a need for developing devices that efficiently convert solar energy to electricity. For a high conversion efficiency in thermal systems, an absorbing surface must have high solar absorptivity and low infrared emissivity. Consequently, research was aimed at obtaining selectively emissive materials for solar heat absorbers. A theoretical analysis was made of absorber-surface efficiencies and selective absorber materials were prepared and tested. The theoretical analysis showed that selective absorbers do have an efficiency advantage over black-body surfaces at temperatures up to 3000 F. Two good selective coatings were developed—a cobalt-oxide deposit and a chrome-nickel-vanadium deposit. The coatings were applied to both polished copper and nickel. The cobalt-oxide surfaces produced an absorptivity of 0.93 and an infrared emissivity of 0.24. The chrome-nickel-vanadium surface had an absorptivity of 0.94 and an infrared emissivity of 0.40.