The efficiencies of thermal collectors are traditionally expressed with respect to the total (direct beam plus diffuse) insolation at the collector plane. Evaluation of the performance of concentrating collectors, however, requires, in addition, a knowledge of the insolation which is within the angular field of view of the collector. The use of pyranometers to measure the total insolation as well as the insolation within specified angular fields of view, together with a normal incidence pyrhe iometer to measure the direct beam component, is described. The instrument calibration procedure is discussed, and several data are presented.
Kent A. Reed, Kent A. Reed,
"Instrumentation For Measuringdirect And Diffuse Insolation In Testing Thermal Collectors", Proc. SPIE 0085, Solar Energy Utilization II, (15 February 1977); doi: 10.1117/12.954944; https://doi.org/10.1117/12.954944