Concentrating (focusing) type solar collector

 

Focusing collector or concentrating type solar collector is a device to collect solar energy with high intensity of solar radiation on the energy absorbing surface. Such collectors generally use optical system in the form of reflectors or refractors. A focusing collector is a special form of flat-plate collector modified by introducing a reflecting or refracting surface between the Solar Radiation and the absorber. In these collectors radiation falling on a relatively large area is focused on to a receiver or absorber of considerably smaller area. As a result of the energy concentration, fluids can be heated to temperatures of 5000 ^oC or more.

 

Figure 2.3 - Concentrating (focusing) type solar collector

A Schematic diagram of a typical concentrating collector is shown in fig. The collector consists of a concentrator and a receiver. The concentrator shown is a mirror reflector having the shape of a cylindrical parabola. It focuses the sunlight on to its axis where it is absorbed on the surface of the absorber tube and transferred to the fluid flow through it.

A concentric glass cover around the absorber tube helps in reducing the convective and radiative losses to the surroundings. In order that the sun’s rays should always be focussed on to the absorber tube, the concentrator has to be rotated. This movement is called tracking in the case of cylindrical parabolic concentrators, rotation about a single axis is generally required. Fluid temperatures up to around 5000 ^oC can be achieved in cylindrical parabolic focussing collector system.