Estimation of Global Solar Radiation
Abstract
Solar radiation is the fundamental renewable energy source that sustains the biosphere and drives its self-organization. Reliable solar radiation data sets are essential to the work of energy planners, engineers and agricultural scientists. Thus solar radiation is a driving variable for a wide range of processes in both natural and human systems. The number of meteorological stations equipped with radiation measuring equipment, as compared to other meteorological parameters, is very few. Furthermore, the present statistics and information on such stations have many record errors. As a result, designing models and reviewing of techniques to estimate the solar radiation are quite useful for applied studies. The objective of this study is the estimation of the global solar radiation, using the Johnson-Woodward (JW) methodology for the first time in Iran and comparing the results derived from this method with meteorological data. This method is an empirical parameter and its sole inputs are the geographical latitude and sunshine hours. To achieve this goal, initially, the model’s empirical parameter was calculated, using the radiation data quality controlled and then using this parameter, the daily global solar radiation was estimated. For this estimation, the data from four synoptic meteorological stations in Tehran Province with long–term radiation statistics was used. To evaluate the estimation results, the statistical methods on error comparison such as Root Mean Squared Error, Mean Bias Error, Mean Absolute Error and correlation coefficient, were used. The results show that the above method used in estimating the solar global radiation has a high degree of accuracy. This model has an overall superior performance for synoptic meteorological stations in Tehran Province. Key Words: Global Solar Radiation, Johnson-Woodward Method, Sunshine hours, Tehran Province.