Technical evaluation of a stand-alone photovoltaic heat pump system without batteries for cooling applications

The coupling of Photovoltaic (PV) and Heat Pump (HP) systems is an attractive alternative for reducing the energy consumption associated to cooling applications, as well as increasing the renewable share in the electric systems. This work presents the results of the technical validation of a stand-alone PV-HP system operating without batteries, for two different control algorithms implemented for the compressor of the HP unit: the Maximum Power Point Tracking control (MPPT) and the inverter control. Both algorithms include a routine for mitigating the solar power fluctuations due to passing clouds, which was able to resist 75% of the clouds registered during the carrying out of the tests. The values of the main Key Performance Indicators (KPIs) traditionally used for the characterization of PV and HP systems -Performance Ratio (PR), Energy Efficiency Ratio (EER) and Seasonal Performance factor (SPF)- were calculated, as well as some new KPIs proposed for PV-HP systems. These new KPIs are proposed to distinguish the loss of performance due to any bad quality of the PV-HP and to external factors such as user behavior or the cooling period. The results show a PR of between 0.17 and 0.5, an EER of between 2.51 and 3.06 and a SPF of between 2.51 and 3.01. The low PR value is explained by the utilization ratios of the system (UREF ranged from 0.27 to 0.77) due to the characteristics of this application, rather than any bad quality in the PV-HP system.