ABSTRACT
An energy-efficient solar collector should absorb incident solar radiation, convert it to thermal energy, and deliver the thermal energy to a heat-transfer medium with minimum loss at each step. Figure 3.1 serves as a convenient introduction to the design of a flat-plate solar collector and outlines the most salient components. The collector comprises a thermally well-insulated arrangement whose upward-facing side is transparent so that solar radiation can penetrate to an absorbing surface, with carefully tailored properties, in contact with a heat-transfer medium such as water or air. Thermal losses are diminished by placing the absorber surface below a cover glass. Even smaller losses can be obtained by the use of transparent insulation in the air gap between the absorber and the cover glass. In principle, the energy efficiency of the collector can be boosted by surface coated glass: antireflection coatings as well as infrared-reflecting coatings are of interest. It should be stressed that Figure 3.1 refers to the commonly used fixed flat-plate collector. Most of the treatment below will be done with such collectors in mind, but some discussion of absorber surfaces designed for high-temperature applications primarily in evacuated tubular collectors is also included. Some solar collector constructions have solar reflecting and tracking facilities.
