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 so lar radiation by estimation. This paper utilizes a geostatistical technique for the estimation of solar radiation in Saudi Arabia. This technique incl udes five steps: (i) data collection, (ii) univariate analysis, (iii) exper imental variogram calculations and model fitting, (iv) estimation using kri ging, and (v) plotting contour maps. Variogram models are fitted to measure d variograms for each month of the year. Estimates were obtained at 1500 gr id points (30 x 50) between a longitude of 36.58 degrees E and 50.00 degree s E, and latitude of 17.17 degrees N and 31.33 degrees N for a grid resolut ion of 55 x 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 techn ique, estimates were obtained at the 41 known locations by systematically e xcluding 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 erro rs 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. (C) 2000 Published by Elsevier Science Lt d.