Solar Averaged Transmittance Properties of Various Glazings

摘要

The solar average transmittance properties of a variety of coated and uncoated plastics (teflon, tedlar, acrylic) and fiberglass composites (e.g., greenhouse coverings) were calculated from the normal hemispherical transmittance measured from 250 to 2500 nm. In addition, the normal hemispherical reflectance for each sample (which includes the reflectance from both sample surfaces) was measured over the same wavelength range. These data were solar averaged over an air mass two solar spectrum for the following cases: (1) an average over the solar energy spectrum as reported separately by Moon and Thekaekara to obtain a solar transmittance which is applicable to a solar thermal collector; (2) an average over the solar photon spectrum to obtain a solar transmittance which is applicable to a solar photon converter; and (3) an average over the solar photon spectrum which has been limited to the active wavelength region of several common solar cells. Solar energy transmittance values for the materials studied ranged from 0.95 to 0.77. The solar energy averages calculated using Thekaekara's data were from 0 to 3.5% lower than the averages calculated from Moon's data. Depending upon the material, the difference between the solar energy average and the solar photon average limited to the active range of a solar cell ranged from 1% to as much as 11%. Thus materials that have a low solar energy transmittance (approximately 80%) when used in thermal systems, may have a higher solar photon transmittance (approximately 90%) when used in photovoltaic systems. (ERA citation 04:000465)