9.1 Receiver Design
The job of the receiver is to absorb as much of the concentrated solar flux as possible, and convert it into usable energy (usually thermal energy). Once converted into thermal energy, this heat is transferred into a fluid of some type (liquid or gas), that takes the heat away from the receiver to be used by the specific application.
Thus far we have concentrated our attention on reflection of incident solar energy and not been concerned with the geometry of the receiver. There are basically two different types of receivers - the omnidirectional receiver and the focal plane receiver.
Rather than deal in complete generality and talk about the many possible types of receivers that could fall into these two categories, we discuss only two widely used receivers, the linear omnidirectional receiver and the point cavity receiver. This will not artificially limit the applicability of the development of the following paragraphs but will provide a nice focus to the discussion.
Figure 9.1 is as photograph of a linear omnidirectional receiver used with parabolic troughs. It consists of a steel tube (usually with a selective coating; see Chapter 8) surrounded by a glass envelope to reduce convection heat losses. As the name ´omnidirectional´ implies, the receiver can accept optical input from any direction.