Optical flux measurements in the focal area of a parabolic trough concentrator

Abstract
Parabolic trough concentrators are an option to use direct solar radiation for the production of process heat or electricity. Besides thermal losses a number of optical errors have to be taken into account during designing reflector and absorber dimensions. In combination, these errors lead to flux density distributions on the surface of the absorber tube, which deviate tremendously from distributions, calculated with the rules of ideal optics. In the present study a circular foil radiometer has been used to measure the flux densities in the focal area of a parabolic trough concentrator with the objective to analyse the influence of various optical errors. The experimental set-up and the measurement system is described in detail. Measured flux density distributions resulting from various changes of parameters like tracking errors, reflector shape accuracy, specular properties of the reflecting materials and position of the absorber tube are presented. The effect of these parameter changes on the flux density distribution is shown additionally by comparison with several simulated distributions, which take into account the above mentioned optical errors.