Experimental investigation of an off-grid photovoltaic heat pump collection system with heat collecting as a core

In this study, an off-grid solar photovoltaic heat pump collection system with heat collection as a core is proposed and experimentally verified. The proposed system consists of coupled photovoltaic and heat pump (HP) systems. In the proposed design, intelligent control strategies are used to ensure that during the day, under high temperature and low humidity conditions, solar energy can be converted into thermal energy. The electricity generated by solar photovoltaic (PV) modules is used to drive an HP for heat collection with a high efficiency. By using an energy storage battery, the proposed system can temporarily store abundant solar energy in the form of electrical energy, thus supplementing the energy required by the HP when solar radiation is insufficient, which improves the PV conversion efficiency. Furthermore, an energy output ratio is introduced to characterize the off-grid photovoltaic heat pump collection system’s operational status. In practical applications, the PV module number has a significant effect on the operating time of HP systems, directly affecting the system’s comprehensive heat collection efficiency (CHCE). A test-bed set up in Lasa, Xizang, China, is used in this study, and a series of all-day experiments are performed to analyze the operational characteristics of the proposed system. This study also discusses the influence of the PV module number and the HP start-up time on the system’s CHCE value. Moreover, an analysis is conducted to determine the relationship between the PV module number and the HP start-up time. The experimental results show that the proposed system has high CHCE and good operational stability when transforming solar energy into heat. The maximum instantaneous CHCE of the proposed system can reach 93 %, and the daily CHCE can reach 72 %. This verifies that the proposed system has research and practical significance, as well as significant application potential.