Experimental investigation and analysis of a direct expansion photovoltaic-thermal heat pump system with optimized solar energy harvesting

• A novel PVT heat pump system with optimized solar energy harvesting is proposed. • Image-acquisition camera is integrated to correct dual-axis tracking precisions. • Entire energy conversion pathway of novel PVT heat pump system is analyzed. • Combined power and heat cogeneration performance under typical days is evaluated. Integrating photovoltaic (PV) and solar thermal technologies offers a promising route for transitioning from traditional to renewable energy sources. This study proposes a novel direct expansion heat pump system integrated with dual-axis tracking photovoltaic-thermal (PVT) modules to enhance solar energy harvesting. A comprehensive mathematical model was proposed to elucidate the entire energy conversion pathway of the direct expansion PVT heat pump system, spanning from incident solar radiation to the system’s available condensing capacity. The model provides a fundamental framework for evaluating the synergistic effects of active tracking and solar-assisted heat pump cycles. To enhance the accuracy of solar harvesting within this framework, a vision-based tracking strategy utilizing an image-acquisition camera is employed to perform solar tracking and automatically mitigate rotational deviations. The proposed model and system performance were rigorously validated through comparative experimental investigations. Moreover, the experiments reveal that under an average incident radiation intensity of 994.9 W/m 2 and an ambient temperature of 27.8 °C, the proposed system achieved an electrical energy yield improvement of 6.4% compared to a dual-axis PV system. At a target hot water supply temperature of 50.0 °C, the system exhibits an average heat gain factor (HGF) of 0.68 and an average coefficient of performance (COP) of 5.9. Performance evaluations across typical meteorological days highlight that the proposed configuration boosts daily COP increase of 4.3%-12.2%, proving its potential as a high-efficiency and sustainable solution for building-integrated electricity and heat cogeneration.