In this paper, we present an experimental and theoretical investigation of the energy storage performance of a model solar pond with a surface area of 2.096 m(2) and a depth of 2.0 m which is built in Cukurova University in Adana, Turkey. The system consist of three different densities zones (e.g., upper convective, non-convective and heat storage). During the months of a year, a data acquisition device was used to determine the temperature at various locations vertically within the pond. In the theoretical part, a mathematical model is used based on finite differences. For this system, the heat losses have been analyzed and modelled by using the Heat 2 software. We developed a performance model to determine the efficiencies of the solar pond. As a result, the total heat losses in side walls and inner insulation zones of the system are found. The experimental and the theoretical heat storage performance of the heat storage zone of the solar pond is determined the highest energy efficiency as 28.41 and 30.16 % for August, the lowest energy efficiency as 8.27 and 10.74 % for January, respectively. The results are compared and hence a good agreement is found.