A novel theoretical model, capable of giving the temporal temperature variation at any point inside or outside a non-insulated rectangular solar pond at any time, is presented. Incorporating the finite difference approach, the model makes use of one- and two-dimensional heat balances written on discrete regions in the brine and in the soil adjacent to the pond. These simultaneous equations are solved for the local temperatures, using a computer program. Values of hourly averaged air temperature and daily averaged soil temperature for the site were used as input parameters, and empirical functions for the time-dependence of these variables were incorporated into the theoretical model. It was found necessary to use this level of detail of the meteorological data for reliable predictions on the solar ponds. The model results are compared with measured results on an actual solar pond built in Cukurova, Turkey. The modelled and experimental temperature profiles are found to be in a very good agreement. The results indicate that the thickness of the salt gradient region of a solar pond should not be less than 1.3 m. Heat losses form the pond side-walls was found not to effect the performance of solar ponds when the surface area is greater than 100 m(2). (C) 1998 Elsevier Science Ltd. All rights reserved.