Enhanced solar energy collection using reflector-solar thermal collector combinations

• Published in: Solar energy 1975-11, Vol.17 (5), p.277-283
• Main Authors: McDaniels, D.K., Lowndes, D.H., Mathew, H., Reynolds, J., Gray, R.
• Format: Article
• Language: English
• ISSN: 0038-092X; 1471-1257
• DOI: 10.1016/0038-092X(75)90044-4

The amount of direct light gathered by a combination of reflector plus flat-plate collector has been analyzed. The calculations were done allowing variable reflector and collector orientation angles, variables latitude, and arbitrary sun hour angle away from solar noon. The effects of reflection and transmission losses and of polarization of the incident light were included. Correction was also made for the finite size of the reflector. It was found that the optimum orientation has the collector plane almost perpendicular to the plane of the reflector. This optimum orientation is approximately independent of the sun's azimuthal dependence. The optimum reflector angle is found to be between 0° and 10° above the horizon for winter solar conditions. For typical winter operating conditions the enhancement in light gathering power for direct solar radiation is about a factor of 1·4–1·7. This results in an effective increase of 100% in the useful winter heat output from a practical reflector-collector combination with a reflector angle of 0°, over the useful heat output obtained with an optimally oriented simple flat-plate collector. An approximate calculation was also made of the overall enhancement in useful heat output for diffuse solar radiation; an increase by a factor of about 1·5 is predicted. Comparison with the preliminary analysis of the performance of the Coos Bay, Oregon solar house shows substantial agreement with the predictions of the present analysis.