In conventional solar water heaters, the thermal energy storage is accomplished by increasing the sensible heat in a fluid. Therefore, the accumulation capacity of sensible heat is proportional to the mass storage and the increase of temperature, so that an increase in the requirements involves a bigger tank volume. Phase change materials (PCM) stored energy at constant temperature (or at least in a fairly narrow range of temperature) while the phase change is produced, they are presented as an alternative to compensate the solar
