An experimental study and a theoretical study have been conducted to evaluate the performance for a closed latent heat energy storage system using energy and exergy analyses. The energy storage tank is neither fully mixed nor fully stratified. It may be considered as semistratified. Experiments were performed on sunny winter days in 1996 in this study a complete storing cycle and charging and discharging periods are considered Energy and exergy efficiencies, total energy and exergy variations, and mean energy and exergy efficiencies are also calculated by using experimental data.