Why is it that ASTEC has “different” solar reflectivity values?
The reflectivity values for ASTEC vary from 85% to 94%. The variability is due to the fact that reflectivity of a given material is “wavelength dependent”. In other words, certain wavelengths of the solar spectrum are reflected more than others. Between the various wavelengths of ultraviolet radiation, visible radiation, and infrared radiation, we obtain “reflectivity” ranging from 85% to 94%. It would be too expensive and impractical to determine the reflectivity of every wavelength in the UV to infrared radiation band. In practice, the industry has adopted a standard which consists in taking the average reflectivity. As for ASTEC, we have taken a more conservative approach by using only the lowest reflectivity: 85%. Normal hemispherical reflectivity: 86.9% Reflectivity for visible radiation: 92.7% Thermal emissivity (infrared): 90% Normal emissivity: 92% Please note that the normal hemispherical reflectivity (86.9%) represents an average reflectivity for ASTEC #900. When we say that
