Solar energy has a promising future as one of the most important types of renewable energy. Solar ponds can be an effective way of capturing and storing this energy. A new theoretical model for a heat transfer in a salinity gradient solar pond has been developed. The model is based on the energy balance for each zone of the pond; three separate zones have been considered, namely the upper convective zone, the lower convective zones, as well as the non-convective zone. The upper and lower zones are considered to be well mixed, which means the temperatures in these zones are uniform. The model shows that the temperature in the storage zone can reach more than 90 degrees C during the summer season whereas it can be more than 50 degrees C in winter if the pond is located in the Middle East. In addition, the time dependent temperature for the three layers has been found. Furthermore, it is concluded that heat loss from the pond's surface occurs mainly by evaporation, in comparison to convection and radiation. Heat loss to the ground has been calculated by using three different equations. It was found that the perimeter of the pond has a significant effect on heat loss to the ground from a small pond, while its effect is small in the case of large pond. The validity of the model is tested against experimental data for several established ponds; good agreement is observed. (C) 2015 Elsevier Ltd. All rights reserved.