Due to the worldwide continuous increase in energy demand and cost, great efforts are exerted to seek, develop, and use alternative energy sources. The solar energy is the cleanest renewable source to be used in many applications. One of these applications is the water solar heater. Being simple, cheap, and has low maintenance, the solar heater has been attracting many researchers to study its performance and seek ways for enhancement.
Previous efforts focused on enhancement techniques as absorber surface modification, using phase change material, nano-fluids, thermal coating, and using porous medium around the absorber. As a proposed idea, the present investigation utilizes the stored thermal energy in sandy soil to warm the flowing water before entering the solar heater collector. An experimental, locally manufactured water solar heater was installed in El Wadi El Jadid region (24 33 latitude and 27 13 longitude).
The results showed an enhancement in the performance of the water solar heater using the thermal energy stored in sand. The daily solar collector efficiency and average outlet water temperature improved by nearly 14.7% and 26%, when sand storage was covered with a plastic transparent sheet and sand was wetted with a certain percentage of waste oil.