Performance analysis and operation optimization of photovoltaic/thermal assisted energy-pile ground source heat pump system in cold regions

The coupling between the photovoltaic/thermal collector and energy piles can store the solar waste heat in the soil via the energy piles, addressing soil thermal imbalance around energy piles, and preventing the decline in electric efficiency of photovoltaic/thermal collector due to high temperature. However, solar thermal energy is subject to losses during transmission when stored underground and subsequently used as the heat source for the heat pump. In contrast, direct utilization of solar thermal energy through different functions-such as preheating, direct heating, and auxiliary heating-can avoid these transmission losses. Despite the promising potential of energy piles, research on optimizing the utilization of solar energy in conjunction with energy piles remains limited. To bridge this research gap, this study proposes multi-functional operation strategies for photovoltaic/thermal-assisted energy-pile ground source heat pump systems, including configurations for heat storage, serial heat source and storage, and parallel heat source and storage. Using system models developed for an office building in the severe cold region of China, the study conducts a comparative analysis of subsystem thermal and electric performances, as well as the overall energy, environmental, and economic impacts. The results indicate that the parallel heat source and storage system achieves the highest solar heat extraction, ranging from 16.95 MWh to 17.25 MWh, due to its significant temperature difference during the heating season, with a utilization ratio of 13.19 %-14.17 %. A higher flow rate to the PV/T subsystem further enhances solar heat extraction, reducing the dependence on soil heat extraction. Additionally, the serial heat source and storage system demonstrates optimal solar energy utilization, achieving a total efficiency of 70.20 %, with electricity production of 225.84 MWh and heat recovery of 732.57 MWh. Finally, the overall performance analysis highlights the serial heat source and storage system as the most suitable configuration. This system achieves the lowest total power consumption (82.48 MWh to 82.60 MWh), carbon emissions (497.31 tCO2), and ten-year costs (60.34 x 104 CNY). This study contributes to the optimization of PV/T-assisted energy-pile ground source heat pump systems, supporting the advancement of low-carbon, energy-efficient building technologies.