The Estimation of Incoming Solar Radiation in Kermanshah Province

Various plannings in agriculture, hydrology, architecture and energy largely depend on the correct estimation of the amount of solar radiation. To estimate the solar radiation, most of the previous studies have used Angstrom model, having the values of sunshine hours as it's input, or regression equations through considering the climatic factors and elements affecting the radiation. In this study, optimized "Bird and Hulstrom" model is used to estimate incoming solar radiation in Kermanshah Province by using the daily data from synoptic weather stations of the province between the years 1990- 2009. For this purpose, all parameters involved in radiation, including length of day, humidity, air mass, air pressure, precipitable water, sky albedo, atmospheric absorption and absorption by ozone were used and the resulting spatial-temporal variations of radiation were analyzed. The results showed that there is little difference between the radiation values measured by pyranometer and values estimated by the model. This indicates the ability of the model to estimate radiation. The least amount of incoming solar radiation in the region occurs in January and December, which varies from 9 to 13 MJ/m2/day in different locations of the province. The amount of radiation absorbed by ozone is reduced in the summer due to the reduction of air mass, especially in the highlands; while the amount of direct radiation and thereby total radiation is increased in this season. The highest amount of incoming solar radiation in the region occurs in June, which varies from 32 to 42 MJ/m2/day in different locations. In autumn and winter, radiation differences in the region are reduced because of the role of diffuse radiation.