Direct Radiation Measurements for the Evaluation of Process Heat Systems with Concentrating Solar Thermal Collectors
Abstract
For the evaluation of the performance of thermal and photovoltaic concentrating solar systems a detailed determination and measurement of the Direct Normal Irradiance (DNI) is essential. The most accurate way of measuring this is with a bi-axial tracking pyrheliometer. However due to its high investment cost and need of maintenance, cost-efficient alternatives are of interest, especially for monitoring projects. This work presents an investigation of the performance and reliability of different alternative devices for the determination of the DNI, which are a sunshine pyranometer SPN1 device and a Rotating Shadowband Irradiometer (RSI). While the pyrheliometer directly measures the DNI via 2-axis tracking, the SPN1 and RSI determine the DNI through the measurement of the global and the diffuse irradiation and the information of the location and solar time. In order to investigate the suitability and reliability of these alternative instruments we have recorded data of about two years in 10 s resolution for the pyranometer SPN1 and pyrheliometer and of about 1 year in 1- minute resolution for the RSI and analyzed the data up to an irradiance of 950W/m2.
Keywords
Direct normal irradiance measurements, Pyrheliometer, Sunshine pyranometer spn1, Rotating shadowband irradiometer rsi