A dynamic simulation model, based upon the thermal-electrical analogy, has been developed to simulate the free thermal behavior of a solar greenhouse. The simple linearized model treats greenhouse air and ground temperatures as lumped parameters. It requires only six input parameters, which were measured on site or obtained from a regional weather-station. Model development focused on radiative transfers through the glazing (i.e. solar input) and within the greenhouse (i.e. re-emitted infrared) and on heat losses by infiltration which were determined experimentally. The model was validated by comparisons with the actual thermal behavior of SERSOL, a solar greenhouse built by students on the campus of the University of Montreal. Data were recorded in SERSOL during 10 days over a 3-month winter period. Several key parameters were adjusted by curve fitting of the results obtained in specially designed experiments. Results obtained over a broad spectrum of weather conditions show good agreement between simulated and actual behavior. The main default of the model appears to be a time shift, which could not be satisfactorily corrected.