Solar beam irradiance is measured for solar energy applications due to two reasons: to determine the
available amount of the solar resource and energy yield at sites selected for an installation or to evaluate
efficiency and proper operation of a concentrating solar power plant. However, the requirements on data and
devices are different for both applications. In this paper, the equipment and methods used at DLR for
improved solar beam irradiance measurements are presented with reachable accuracy for both applications.
Different thermal irradiance sensors are compared among each other and to an absolute cavity radiometer.
The sensors are calibrated with the absolute cavity radiometer to get utmost accuracy for precise field
measurements. Besides, they are subsequently used for the calibration of RSP sensor heads for remote
automatic weather stations, which reach a mean accuracy of 3%
