Solar energy collected at a number of discrete sites, which are dispersed over a geographical area, will exhibit both spatial and temporal variability. Being able to model this variability will have many applications, Fur example in controlling an electricity system that is supplied by decentralised PV arrays. This paper describes a statistical modelling study of solar data that were recorded over 2 years at a total of 22 sites in the city of Edinburgh, Scotland, and in the nearby Pentland hills. A spatio-temporal model is proposed for global irradiation on a horizontal plane: this incorporates the sum of two exponentials to model the decrease in covariance between sites with time lag, and a space-time term to model the combined dependence of covariance on time lag and easterly distance. (C) 2001 Elsevier Science Ltd. All rights reserved.