Studying the level of solar radiation is important for problems related to both environmental pollution and alternative energy development. In this work a space-time model for solar radiation in the Tyrrhenian basin is presented. Three main features of the model must be stressed because of their importance in modelling space-time variability of a phenomenon. The first and most important one is that relations between solar radiation in different sites are an outcome of the model’s estimation procedure. With this approach spatial weights are not bound to be symmetrical and proportional to distance between locations or to be constant over time. The second one is the presence of a simultaneous effect among locations as the solar radiation in one of them is a function of what simultaneously happens in all the other ones. The third main feature of the model is represented by constrained estimation on the basis of a priori knowledge about the phenomenon that allows to cope the problem of the increased number of parameters.