Experimental performance of three solar collectors

Abstract

Simultaneous testing of solar collectors is important for the determination of accurate comparative performance data. Three flat-plate solar collectors were tested for over six months: a water trickle collector, a typical collector with double glazing, and a thermal trap collector. The first two collector types have been previously tested by other investigators, but the development of the thermal trap collector is unique to New Mexico State University, where in 1964 work was initiated on this type of collector. The thermal trap collector employs a transparent solid (methyl methacrylate) adjacent to the fluid cooled collector plate. It is found that by the use of this transparent solid, which has a high transmittance of short wavelengths combined with a low transmittance of long wavelengths and a small thermal conductivity, high temperatures can be achieved. The comparative collector tests were performed for a variety of operational conditions. The collector efficiencies were experimentally determined, and analysis of the collector losses was accomplished. The thermal trap collector was found to have a higher operational efficiency than the other collector types and is capable of collecting solar energy for a longer period of time each day. At operating temperatures above 145°F, the thermal trap collector is more than twice as efficient as the water trickle collector. © 1975.