FEW SITE-INDEPENDENT MODELS FOR ESTIMATING GLOBAL SOLAR RADIATION FOR WEST AND SOUTH ASIAN COUNTRIES

Knowledge of the global solar radiation (GSR) at a place is necessary in selecting the suitable site for implementing solar energy projects. For under-developed and developing countries, there is a very low spatial density of meteorological stations equipped for radiation observation. Hence, the numerical methods become a useful alternative. Here, measured data of geographical and meteorological (geo-met) parameters of 90 stations across Asian countries is used to develop siteindependent GSR estimation models. These parameters are longitude (ᵩ), latitude (λ), mean sea level (MSL) and daily averages of maximum air temperature (Tmax), minimum temperature (Tmin), percentage relative humidity (%RH), temperature difference (ΔT) ratio of minimum to maximum temperature (Tmin/ Tmax). Apart from the above data, data from 5 other stations is used for model validation. Root mean square error (RMSE) is used to assess the quality of the GSR estimates. 6 new models considering different combinations of geo-met parameters as variables are proposed. Observed RMSE ranges from 3.3% to 4.4%. With the test data, new model M-3 (with ᵩ %RH as variables) gives RMSE of 2.9% and the simplest model M-5 (with MSL, ᵩ,λ, %RH as variables) gives a RMSE of 1.87%.