Spatial estimation of global solar radiation using geostatistics

The number of radiation data collection stations is limited due to economic reasons. Hence, there is a need for the spatially continuous mapping of solar radiation by estimation. This paper utilizes a geostatistical technique for the estimation of solar radiation in Saudi Arabia. This technique includes five steps: (i) data collection, (ii) univariate analysis, (iii) experimental variogram calculations and model fitting, (iv) estimation using kriging, and (v) plotting contour maps. Variogram models are fitted to measured variograms for each month of the year. Estimates were obtained at 1500 grid points (30 × 50) between a longitude of 36.58°E and 50.00°E, and latitude of 17.17°N and 31.33°N for a grid resolution of 55 × 33 km. These values were used to plot the contour maps of solar radiation for each month of the year. To test the performance of the technique, estimates were obtained at the 41 known locations by systematically excluding one of these points from the known data. The error analysis showed a maximum mean deviation between measured and estimated values of 0.0037 (January) and a minimum of 0.0013 (March and October). The mean percent errors were found to vary between a minimum of 0.5% and a maximum of 1.7%. This technique may be expanded for the spatial estimation of solar radiation on regional and continental scales.