This paper describes an improved approach for (a) the estimation of the mean expected hourly global solar radiation I(h;n(j)), for any hour h of a day nj of the year, at any. site, and (b) the estimation of stochastically fluctuating I(h;n(j)) values, based on only one morning measurement of a day. Predicted mean expected values are compared, on one hand with recorded data for the period of 1995-2000 and, on the other, with results obtained by the METEONORM package, for the region of Patra, Greece. The stochastically predicted values for the 17th January and 17th July are compared with the recorded data and the corresponding values predicted by the METEONORM package. The proposed model provides I(h;nj) predictions very close to the measurements and offers itself as a promising tool both for the on-line daily management of solar power sources and loads, and for a cost effective PV sizing approach. (c) 2006 Elsevier Ltd. All rights reserved.