Experimental investigation of the performance of a PVT heat pump soil cross-seasonal energy storage system across various operation modes

To improve the energy efficiency of a photovoltaic thermal (PVT) heat pump system designed for soil-based cross-seasonal energy storage, this study empirically evaluates its performance across multiple operational modes. The system operates in eight distinct modes: soil source heat pump (SSHP) heating, a combination of PVT heating and SSHP heating (PVTSSHP heating), PVT heat pump (PVTHP) heating, standalone PVT heating, soil cooling, SSHP cooling, PVTSSHP cooling, and PVT heating with soil energy storage. Experimental analyses are performed to explore system behavior under representative annual conditions. Under these typical conditions, the system COPs for SSHP heating, PVTSSHP heating, PVTHP heating, PVT heating, soil cooling, SSHP cooling, and PVTSSHP cooling are determined as 4.1, 3.2, 4.2, 10.5, 10.6, 3.3, and 2.7, respectively. The heat pump COP for SSHP heating, PVTSSHP heating, PVTHP heating, SSHP cooling, and PVTSSHP cooling are recorded as 5.9, 6.8, 7.9, 5.0, and 4.9, respectively. Additionally, the thermal efficiency of the PVT array under different operational modes is measured at 27.0 % for PVTSSHP heating, 20.0 % for PVTHP heating, 14.2 % for PVT heating, 48.9 % for PVTSSHP cooling, and 32.9 % for PVT heating soil mode. The electrical efficiency of the PVT array is reported for all modes as 16.9 %, 16.5 %, 16.4 %, 16.0 %, 14.7 %, 15.5 %, 16.0 %, and 16.4 %.