Chapter three - Solar Energy Collectors

Abstract

This chapter reviews various types of solar energy collectors currently available. It also analyzes the optical and thermal collectors. There are basically two types of solar collectors: nonconcentrating or stationary and concentrating. A nonconcentrating collector has the same area for intercepting and absorbing solar radiation, whereas a sun-tracking concentrating solar collector usually has concave reflecting surfaces to intercept and focus the sun's beam radiation to a smaller receiving area, thereby increasing the radiation flux. Concentrating collectors are suitable for high-temperature applications. Solar collectors can also be distinguished by the type of heat transfer liquid used and whether they are covered or uncovered. The basic parameter to consider is the collector thermal efficiency. This is defined as the ratio of the useful energy delivered to the energy incident on the collector aperture. The incident solar flux consists of direct and diffuse radiation. While flat-plate collectors can collect both, concentrating collectors can utilize direct radiation only if the concentration ratio is greater than 10. Further the optical analysis of CPC collectors deals mainly with the way to construct the collector shape.