Accurate measurements of direct irradiance are required for precise performance analysis and fault detection of concentrating solar process heat plants for industrial processes (CSHIP). For this reason, a cost-effective and low-maintenance pyranometer SPN1 has been investigated by comparing four years minute mean direct normal irradiance measurements of a SPN1 to a reference pyrheliometer at the Institute for Solar Technology SPF in Rapperswil (Switzerland). A significant overestimation of the direct normal irradiance ...