Evaluation of Portable Optical Property Measurement Equipment for Solar Selective Surfaces

Abstract

The operation and accuracy of portable optical measurement equipment for determining the solar absorptance, αs , and emittance, ε, of solar selective surfaces are presented. The optical equipment includes a Gier Dunkle Solar Reflectometer (Model MS-251) and a Willey Alpha Meter (Model 2150) for αs measurements and a Gier Dunkle Infrared Reflectometer (Model DB-100) and a Willey Ambient Emissometer (Model 2158) for ε measurements. The accuracy of the MS-251 for measurements of αs for electrodeposited black chrome coatings was determined to be better than ±0.03 absorptance units. For the same coatings, the Willey Alpha Meter accuracy was limited by deviations up to 0.11 absorptance units. The accuracy of the Gier Dunkle Infrared Reflectometer for ε(100°C) measurements is better than ±0.02 emittance units. Values for ε(100°C) determined with the Willey Emissometer using black chrome coatings are higher than the actual 100°C emittance. However, since the relationship is linear, the correct emittance can be calculated by multiplication by a constant factor.