A Benchmark of Simple Measurement Systems for Direct Irradiance

Kurzfassung

Accurate direct normal irradiance (DNI) measurements are essential for the design and the operation of concentrating solar power systems. Several measurement systems for DNI are available to users, but all commonly used systems still have drawbacks. Sun trackers with pyranometers and a pyrheliometer are expensive and require permanent checks and maintenance by qualified personnel, for example due to tracking errors and soiling effects. Simpler, i.e. more economic and robust sensors may have shortcomings regarding accuracy under various atmospheric conditions and might not be significantly less susceptible to soiling and user errors. Validations and benchmarking of simple radiometers for solar energy applications have been presented. To the best of our knowledge, no benchmarking study is available which evaluates some more recent simple measurement systems which are relevant for solar applications in 2023. Furthermore, most previous benchmarking studies did not measure atmospheric parameters like circumsolar irradiance which may directly influence the measurements of these sensors. We close this gap by benchmarking relevant measurement systems (Rotating Shadowband Irradiometer RSI and Rotating Shadowband Pyranometer RSP 4G; Delta-T SPN1, EKO MS-90, PyranoCam, Sunto CaptPro) at multiple sites. We also evaluate the influence of relevant atmospheric parameters which we measure with dedicated instruments at one site. We include the PyranoCam system in our benchmarking, a novel radiometer system suitable for all solar irradiance components including DNI. It consists of a pyranometer and a fisheye camera that takes photos of the whole sky and employs a combined physical and machine-learning model. The results of the study provide improved estimates of the sensors’ accuracies for a specific application and climatic condition and can assist in the development of corrections for the sensor technologies.