Effect of circumsolar radiation on the accuracy of pyrheliometer measurements of the direct solar radiation

An effort underway to use specially developed circumsolar telescopes to measure the angular and wavelength dependence of the circumsolar radiation for application to concentrating solar energy systems is described. Data from these instruments are used to provide information on the pyrheliometer overestimate. Sample measurements of the telescopes, the range to values (overestimates) obtained over the course of a month, and the long term average effect are presented. A brief discussion is given on the relationship of the results to concentrating solar energy systems.