Experimental study on a hybrid energy system with small- and medium-scale applications for mild climates

This paper presents the design and performance of a hybrid energy system. The hybrid energy system consists of a standard air-conditioning unit (i.e., a split system), with an integrated boiler for heating water. The entire system is driven by a small off-grid photovoltaic plant and was tested at a geographical location with a typical Mediterranean climate in the summer. Three different working regimes were analyzed: a daytime working regime, a nighttime working regime, and an intense working regime. The boiler water consumption was also simulated to investigate its effect on the overall performance of the hybrid energy system. Experimental measurements in different work regimes indicated that the hybrid energy system achieved a COPc between 5.0 and 6.0. The mean engaged electric power of the compressor ranged between 500 and 700 W. The mean temperature of the water heated in the boiler ranged from 43.1 °C to 51.0 °C, with a maximum recorded value of 60.6 °C. The research results demonstrate that the hybrid energy system could be implemented in small- or medium-scale residential touristic facilities for countries with mild climates, where heat pump systems can be used to achieve relatively high seasonal COP (coefficient of performance) values.