Solar Engineering of Thermal Processes, 4th Edition

Chapter 6

Flat-Plate Collectors

A solar collector is a special kind of heat exchanger that transforms solar radiant energy into heat. A solar collector differs in several respects from more conventional heat exchangers. The latter usually accomplish a fluid-to-fluid exchange with high heat transfer rates and with radiation as an unimportant factor. In the solar collector, energy transfer is from a distant source of radiant energy to a fluid. The flux of incident radiation is, at best, approximately (without optical concentration), and it is variable. The wavelength range is from 0.3 to , which is considerably shorter than that of the emitted radiation from most energy-absorbing surfaces. Thus, the analysis of solar collectors presents unique problems of low and variable energy fluxes and the relatively large importance of radiation.

Flat-plate collectors can be designed for applications requiring energy delivery at moderate temperatures, up to perhaps above ambient temperature. They use both beam and diffuse solar radiation, do not require tracking of the sun, and require little maintenance. They are mechanically simpler than concentrating collectors. The major applications of these ...