Feasibility of a High Efficiency Solar Air Conditioner Powered by DC Current

The feasibility of direct use of photovoltaic energy to supply cooling demand of a building is investigated at a demonstration site through its design, installation and evaluation. The cooling is accomplished by using a novel method of energy supply, including photovoltaic panels, electrically driven solar-assisted heat pump, in-house developed inverter and thermal energy storage system.The refrigeration unit is based on a variable speed heat pump, which is supplied by direct current (DC) from photovoltaic panels. In order to provide appropriate current and voltage with high energy transform efficiency, a novel inverter is developed. While in conventional systems four energy transform stages are needed to supply a variable speed heat pump, by this method conversions are reduced to two. In addition, a modular structure of the inverter improves the transformation efficiency, particularly in partial load condition. Although, using this technology reduces the number of energy transformations and losses, but intermittency and variability of PV power will be transferred to the heat pump and the cooling power accordingly. Therefore, a kind of energy stabilizer system is necessary to control the energy fluctuation. Hence, a 30 m3 water tank is used as the thermal energy storage system. The heat pump can be fed simultaneously by both PV and grid power through two separate interfaces. Thus, no additional backup system is needed.