Interannual variation of measured atmospheric solar radiation extinction levels

•Solar extinction measurements are compared and analysed at PSA.•Extinction shows seasonal behaviour and dependence on meteorological variables.•The extinction levels measured during two consecutive years are coincident at PSA.•The CIEMAT system is validated with two years of extinction measurements. Solar radiation loss by attenuation throughout the heliostat-receiver pathway in concentrating solar power plants is a daily factor to consider in order to know the real power production efficiency and performance of this kind of plants. A direct real-time extinction measurement system has been developed at Plataforma Solar de Almería. The system is running from June 2017 and could be installed in other plants. The system is used as a reference system for other extinction methodologies with which they are compared to validate results. Therefore, two years of measurement have been analysed to verify the reliability of the system and to conclude if it can be used as a reference. The study clearly shows that the extinction has a seasonal behaviour and a high dependency on meteorological parameters, episodes of humidity, aerosol and particle concentration. It has also been proven that the system is capable of detecting extinction variations due to the presence of meteorological phenomena. The annual extinction levels measured are coincident in both years analysed, within the error range of the measurement system (≈2%). The measured extinction coincides with the extinction obtained with other methodologies using aerosol data and typical meteorological years.