Operation characteristics of the composite system for combing solar PV/T collector and ground-coupled heat pump

Abstract: Photovoltaic/thermal (PV/T) system can absorb the solar energy, while generating electricity and heat, due mainly to its combining the photovoltaic and solar thermal hybrid energy conversion. PV panels as core components of PV/T system are generally cooled under the circulating fluid for high efficiency of power generation in the utilization of solar thermal energy. As such, a current PV/T system can offer electricity and heat for the building, while effectively shorten the investment cycle, compared with the PV system. Lastly, a solar PV/T collector and a ground-coupled heat pump (PV/T-GCHPs) are combined to serve as an improved energy supply system for the complementary utilization of solar energy and shallow geothermal energy. In this study, a PV/T-GCHPs mathematical model was presented for the cooling/heating demand of a 6-floor employee apartment, further to evaluate the performance of the system when simulating the operation characteristics. The results showed that the surface temperature of PV panels decreased significantly, due mainly to the cooling effect of the borehole heat exchanger (BHE) in the PV/T-GCHPs, indicating a higher PV efficiency than before. The temperature of PV panels in the PV/T-GCHPs was 44.69% lower than that of the PV system at noon on a typical day (April 2), whereas the PV efficiency was 12.12% higher than that of the PV system at the same time. The total power generation increased by 20 322 kWh in the power generation of PV panels in the PV/T-GCHPs, compared with the PV system in 20 years. The maximum monthly power generation increased 13.62%, while, the minimum monthly power generation increased 8.67%, compared with the PV system in the first year of PV/T-GCHPs operation. The minimum monthly average PV efficiency was 16.23% in the PV/T-GCHPs, 4.47% higher than that in the PV system. The solar energy was used to charge the ground in the whole life cycle of PV/T-GCHPs (20 years). The average temperature of ground corresponding to the 175 200 h was 2.5 ℃ higher than that in the GCHPs. The ground temperature was kept from dropping rapidly, which was caused from the imbalance of cooling and heating loads in buildings. The total length of BHEs in the PV/T-GCHPs was shortened by 600 m than that in the GCHPs under the same building load. The 20-year mean coefficient of performance (COP) of PV/T-GCHPs was 5.21 in the whole life cycle, 32.23% higher than that of GCHPs through the initial investment of BHEs in the PV/T-GCHPs system. There was a significant economic benefit in the direct cost saving (in this case of 77 192.45 Yuan cost-saving), compared with the GCHPs in the life cycle. The finding can provide a promising theoretical foundation for the popularization and application of the PV/T-GCHPs system in cold regions of China.