Performance Assessment of an Integrated Sensor for Simultaneous Measurements of Global and Diffuse Radiation Components at Athens Area

The proper design of installations utilizing solar radiation requires the accurate knowledge of solar radiation availability on horizontal and tilted surfaces as well as its direct/total and diffuse components. The measurement of diffuse radiation normally requires a sun tracking or shading device. However, a new integrated instrument, model SPN1, has been presented by Delta-T Devices, incorporating seven miniature thermopile sensors, a built-in microprocessor, and an internal shading device with no moving parts. SPN1 sensor is able to perform simultaneously measurements of both the global and diffuse solar radiation reaching a horizontal surface and can also estimate sunshine duration. Such a sensor was installed at NOA’s actinometric station at Penteli site, during summer 2011, to assess its performance against classic measurements of global irradiance by thermopile pyranometer and diffuse with a shading ring. Stated accuracies are easily verified for 1-min measurements of total solar radiation, with RMSE values varying between 2.6% and 3.6%, whereas for the diffuse radiation, stated accuracies were not possible to verify, with RMSE values varying between 10.8% and 17.0%. This may be due to measurement inaccuracies, yet for the diffuse component there might be a need for a correction factor to improve accuracies.