Design and performance of an off-grid solar combisystem using phase change materials

An off-grid solar combisystem with built-in latent heat storage unit is designed and developed for active space and water heating during day and passive space heating during night. A flat plate solar thermal collector and a photovoltaic module with a Li-Ion battery power the fully autonomous system. The optimized solar combisystem design comprises a heat transfer loop for simultaneously charging phase change material and water. The combisystem can consistently heat the water to about 45 °C during a normal sunny day and retain thermal energy for two days. In addition, the system can also heat the space to a comfortable zone during day and from dawn to dusk along with water heating during winter season, even in fluctuating weather condition. The average energy saving ratio and energy saving obtained during winter season space heating are about 56 % and 4.4 kWh, respectively. The solar combisystem performance shows that the average energy saving ratio and energy saving obtained for space heating were ~ 93% and ~ 2.8 kWh, respectively. It was observed that the air temperature in the phase change material integrated space unit (area coverage ~60%; melting point: 23 °C) remain ~ 4 to 6 °C cooler than corresponding without phase change material integrated space unit. The long-term performance evaluation of the solar combisystem shows that the off-grid system can efficiently maintain the space temperature in a comfortable zone during cooler and warmer season along with water heating for residential application. It is evident that the off-grid phase change materials integrated solar combisystem can lead to significant energy saving in residential buildings both in colder and warmer weather conditions.