Soiling effect on the performance of solar radiometers in composite climatic zone of India

The effect of soiling on the performance of solar radiometers was studied at the national capital region of New Delhi, which is one of the top-ranked polluted cities in the world according to the World Health Organization (WHO). The test pyranometer and pyrheliometer were never cleaned during the soiling test period for around two months. Dust accumulation was allowed on the glass surface of pyranometer's hemispherical glass dome and pyrheliometer aperture glass for two months. The reference pyranometer and pyrheliometer were cleaned on daily basis and measurements were recorded. The test sensors were never cleaned but got washed by rain during the intermittent test period. The transmittance of photons through the glass dome of pyranometer and aperture glass of pyrheliometer is reduced due to dust accumulation on glass surface resulting in measurement of lower irradiance values by test solar radiometers compared to reference solar radiometers. Determined rRMSE value were found to be increasing with time due to soiling on pyranometer and pyrheliometer and reached maximum value of around 12% and 14% respectively during the test period. The per-day rRMSE value for pyranometer and pyrheliometer are 0.28% and 0.20% respectively. During the test period, irradiation values were found to be lowered by 0.21 kWh/m
²
/day for the soiled pyranometer sensor with respect to reference pyranometer sensor. Based on this study it is suggested that weather station sensors in composite climatic zones need to be cleaned on a regular interval to avoid measurement of lower irradiance value by sensors.