Solar thermal collectors and applications

Concentrating collector acceptance angle

Another test required for the concentrating collectors is the determination of the collector acceptance angle, which characterises the effect of errors in the tracking mechanism angular orientation.

This can be found with the tracking mechanism disengaged and measuring the efficiency at various out of focus angles as the sun is travelling over the collector plane. An example is shown in Fig. 22 where the angle of incidence measured from the normal to the tracking axis (i. e. out of focus angle) is plotted against the efficiency factor, i. e. the ratio of the maximum efficiency at normal incidence to the efficiency at a particular out of focus angle.

A definition of the collector acceptance angle is the range of incidence angles (as measured from the normal to the tracking axis) in which the efficiency factor varies by no more than 2% from the value of normal incidence [108]. Therefore from Fig. 22, the collector half-acceptance angle, 0m, is 0.5°. This angle determines the maximum error of the tracking mechanism.