Validation of Direct Beam Irradiance Measurements From Rotating Shadowband Irradiometers in a Region With Different Atmospheric Conditions

Abstract

Rotating shadowband irradiometers (RSIs) are a common type of radiation sensors for measurement of direct normal irradiance (DNI) at remote sites where daily maintenance of the instruments is not feasible or practicable. Their primordial lower accuracy due to systematic deviations of the photodiode response can be improved significantly with a thorough calibration of each RSI against high precision sensors and application of suitable corrections on the raw data. With different available correction functions for the systematic errors, RSI data coincide with first class reference sensors within 2–3% root mean square deviation (RMSD) for 10 min averages of DNI and meet the annual irradiation sum within 1.5%. Such comparisons of RSI data to reference irradiances have only been published for a small number of sites. To endorse the credibility of RSI measurements, it has to be shown that these accuracies derived for certain locations are also valid at other sites with differing atmospheric conditions. Therefore, a parallel measurement campaign with six RSIs and a reference station with first class and secondary standard instrumentation has been performed in the in the extreme climate of the United Arab Emirates (UAE). The results of this comparison are presented in this paper. The stated empiric accuracy could be validated and confirmed for the UAE.