Three different methods are currently proposed to forecast solar radiation. The first is based on time series models, which use a series of the daily average of the measured solar radiation as input data. It has been shown in different papers that a RMSE of 5.1 % [7], 8.3 % [8], and 8.4 % [9] can be obtained, for local predictions using ANN — wavelet methods. Whereas in [7] and [8] the Continuous Wavelet Transform (CTW) is used, [9] employs the Discrete Wavelet Transform (DWT). The author of [8] uses the day number of the year and defuzzficated cloud cover information from the weather forecast service, as auxiliary information. These models are applicable for sites where the solar radiation was measured during one year [7], two years [8], or longer time intervals [7], [9]. The second method is able to forecast the motion of clouds using satellite imaging over the earth surface. It can forecast the solar radiation for any site or area, but the uncertainty related to the utilized models increases substantially over 22% to 30%, for forecast horizons larger than six hours, as reported by Lorenz [10]. The author obtained the former value for low and the latter for high cloud variability. The third method, used in the present article, is based on the NWP with its statistical correction MOS.