Solar Engineering of Thermal Processes, 4th Edition

Chapter 5

Radiation Transmission through Glazing: Absorbed Radiation

The transmission, reflection, and absorption of solar radiation by the various parts of a solar collector are important in determining collector performance. The transmittance, reflectance, and absorptance are functions of the incoming radiation, thickness, refractive index, and extinction coefficient of the material. Generally, the refractive index and the extinction coefficient of the cover material are functions of the wavelength of the radiation. However, in this chapter, all properties initially will be assumed to be independent of wavelength. This is an excellent assumption for glass, the most common solar collector cover material. Some cover materials have significant optical property variations with wavelength, and spectral dependence of properties is considered in Section 5.7. Incident solar radiation is unpolarized (or only slightly polarized). However, polarization considerations are important as radiation becomes partially polarized as it passes through collector covers.

The last sections of this chapter treat the absorption of solar radiation by collectors, collector-storage walls, and rooms on an hourly and on a monthly average basis.

Reviews of important considerations of transmission of solar radiation ...