Field Experiences with the Operation of Solar Radiation Resource Assessment Stations in India

AbstractWorld's largest DNI measurement network of 51 automatic meteorological stations with solar radiation instruments fulfilling the highest commercially available standards is operating in India. The Indian Ministry of New and Renewable Energy (MNRE) in 2011 started this extensive solar resource monitoring cum meteorological station network under the Solar Radiation Resource Assessment (SRRA) project. This paper highlights the overall performance of the stations over more than one year and documents the specific problems and errors observed in field operation. Following best practices quality assessment tests, a data flagging system to identify, differentiate and quantify different types of errors and other functionalities have been implemented as part of the SolMap project. The quality assessment tests check the plausibility of data, differentiate trustworthy data from likely erroneous data and flag them accordingly. The quality flag statistics of all 51 stations reveals that some stations are performing very well and others need more attention to improve. In the period from January 2012 to March 2013 on an average over all 51 stations, 92% of the solar radiation data are classified as correct. The quality control system has proven to be very effective for detecting errors in functionality of the stations. Values flagged erroneous along with missing values are considered as gaps. Many applications such as solar energy performance simulations need continuous time-series. Therefore it is required to fill the measurement gaps with reasonable data. This paper also describes a set of procedures called ‘basic gap filling’ for solar irradiance. The accuracy of the applied basic gap filling methodology is tested and the results show a mean bias of ca. 3% over GHI, DNI and DHI over all types of gaps. Automated alarms, sensor cleaning switch, bird protection cages for wind sensors etc. are some of the efforts SRRA took for smoother operation. Regular cleaning of the radiometers remains the most challenging task for the SRRA network