Use of rainfall data to calculate incident solar radiation in Tropical countries

Abstract

Determining the incident solar radiation for a given location is an important aspect of any solar related application. Though solar radiation data are available at weather stations, localized nature of solar radiation due to topographic and climatic parameters demands measured or calculated solar radiation values for a given location for accurate results. Many correlations have been developed over the past few decades yielding solar radiation values from various weather parameters such as daily sunshine duration, ambient temperature difference, relative humidity, cloud cover etc. However, most of the weather data are practically difficult and costly to record hence requiring a simplistic approach to the issue. For any geographical location the cloud cover plays a major role in controlling the incident solar radiation. In tropical countries, where the climate is highly humid, cloud cover is closely related to rainfall. Therefore, day time rainfall data can be taken as representative of overcast and clear days, paving the way to calculate the clearness index, KT using equations developed on cloud cover data.