Comparison of the effect of outdoor exposure on the optical properties of solar mirrors and transparent encapsulant materials

Technical Report · Tue Sep 01 04:00:00 EDT 1981

DOI:https://doi.org/10.2172/5283302· OSTI ID:5283302

Dake, L S; Lind, M A; Maag, C R

The effects of outdoor exposure on solar mirrors and transparent encapsulant materials are assessed and compared. The encapsulant materials tested included glasses, polymers and silicones. Samples of the materials were placed on stationary exposure racks in six locations that represented urban, desert, oceanside and high altitude mountain areas. Samples were removed periodically for optical characterizations. The spectral hemispherical and diffuse reflectance of the mirror samples and the spectral hemispherical transmittance and diffuse reflectance of the encapsulant materials was measured. The relative normal hemispherical transmittance of the encapsulant materials was measured. Correlations between the glass and mirror data showed that the average diffuse reflectance losses were six times larger for the mirrors than for the glass samples. The average specular reflectance losses for the mirror samples were seven times as large as the average hemispherical transmittance losses for the glass samples. These correlations may enable one to predict the performance of mirrors made using the other encapsulant materials for superstrates. It was found that the urban and oceanside sites were the dirtiest, while the desert and mountain sites were the cleanest. Average specular reflectance losses varied from 4% at the cleanest site to 50% at the dirtiest site. The range in hemispherical transmittance losses for the encapsulant materials varied between 0% and 6%. At one site, the average daily specular reflectance losses were .04% for the mirror samples and average daily hemispherical transmittance losses were about .01% for the glass samples. The polymer materials degraded somewhat more rapidly than the glasses, and the silicones irreversible degraded too rapidly and severely to be useful for either photovoltaic or solar thermal applications.

• Research Organization: Battelle Pacific Northwest Labs., Richland, WA (USA)
• DOE Contract Number: AC06-76RL01830
• OSTI ID: 5283302
• Report Number(s): PNL-4074; ON: DE82005863
• Country of Publication: United States
• Language: English

Related Subjects

14 SOLAR ENERGY
141000* -- Solar Collectors & Concentrators
ARID LANDS
CONTAMINATION
DESERTS
ENCAPSULATION
GLASS
LIGHT TRANSMISSION
MATERIALS TESTING
MIRRORS
MOUNTAINS
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
POLYMERS
SEAS
SILICONES
SILOXANES
SPECTRAL REFLECTANCE
SURFACE WATERS
TESTING
URBAN AREAS
WEATHERING