In regard to restriction of fossil source and their effects on nature, using of renewable sources of energy has been developed and used in recent decades. One of renewable and clean sources of energy is solar energy. Iran with having around 10 16 MJ of annual radiation of sun is a very good location for using and converting solar radiation. In sight of intermittent nature of radiation and heat use, storing produced heat is inevitable. Storing heat as “sensible” in a medium – such as water – is a common way in solar heaters. Employing latent heat of Phase Change Material (PCM) in solar heaters is a noble way of conserving heat. Reduction in the time for preparing hot water, supplying hot water with a temperature nearer to our demands, energy density conserved in tank, degree of lasting hot water and 2 nd law of thermodynamics for heater are study goals in our experiments. In this research a kind of paraffin wax with some special properties, as a suitable PCM for our demands, in spherical capsules has been used in the tank of our model solar heater. Five previous parameters compared before and after use of PCM. Experiments are carried out at two categories to model passive and active solar heater. Results indicate improvement in the behavior of our new solar heater. The best improvement has indicated in passive solar heater which from five parameters three parameter is better for it.
