It is essential that the designer of a solar thermal system be able to accurately size the size the collector field, energy storage requirement, and other system components in order that a given heat load be satisfied. This requires the capability to accurately predict the energy output by the solar collectors and an hourly calculation of the energy balance of the solar facility. The system design is usually based on a wide variety of operating conditions as experienced by the solar system for a typical year of operation. Not only do the solar radiation and ambient temperature vary throughout the day, but also the incident angle of the solar radiation as well which, for the case of a one-axis tracking concentrator, also has a large effect on collector performance. As a result it is important that the collector-testing methods and the performance-prediction technique be consistent and capable of accurately predicting the solar collector energy,output.

Herein is presented the results of the measurements of normal incidence collector performance, i.e., thermal efficiency, and the incident angle modifier for a one-axis tracking parabolic trough concentrator. The collector efficiency has been determined by three different test facilities using different evaluation techniques. In addition, two measurements of incident angle modifier have been made and are presented along with a calculation of the optical effects of nonnormal incidence on the collector efficiency. Finally, the measured performance of a single collector group along with data for two large collector fields are presented and compared, with the results using the current prediction technique for, collector performance.