## 6 Conclusions  
This study delves into the impact of solar radiation intensity on the direct-expansion solar PVT heat pump system, systematically analyzing the variations in PVT panel temperature, electricity generation, photovoltaic efficiency, and COP through comparison with traditional PV panels. The main conclusions of this paper are as follows:  
1. Under different weather conditions, the system exhibits varying operational states. On sunny days, the system enters a high radiation range, while under cloudy and overcast conditions, radiation intensity fluctuates significantly. The return and discharge temperatures of the compressor increase with solar radiation, indicating partial cooling effects. In sunny and overcast conditions, the overall discharge temperature of the system initially rises and then falls, while the back temperature fluctuates between \(-\)13.5 and 24 \({}^{\circ}\)C. Under conditions with an average ambient temperature of 16.5 \(\pm\) 0.5 \({}^{\circ}\)C and an average solar radiation intensity of 510 W\(\cdot\)m\({}^{-2}\), the average temperature difference between discharge and return air temperatures ranges from 81.65 to 83.02 \({}^{\circ}\)C, with the final discharge temperature reaching \(-\)11 \(\pm\) 2 \({}^{\circ}\)C.
2. The system demonstrates significant performance superiority over PV panels under sunny, overcast, and cloudy conditions, achieving temperature decreases of 12 \({}^{\circ}\)C, 11 \({}^{\circ}\)C, and 19 \({}^{\circ}\)C, respectively, compared to PV panels. The temperature slope remains consistent at approximately 0.01 K/W\(\cdot\)m\({}^{-2}\), indicating the stable and uniform response of the PVT panel to solar radiation. Furthermore, the decrease in temperature curve intercepts from 2.13 \({}^{\circ}\)C to 2.44 \({}^{\circ}\)C highlights the system's excellent adaptability to environmental changes. There is a certain degree of discrepancy between experimental and theoretical data, with larger errors observed in the overcast conditions.  
Figure 16: Linear Relationship and Prediction of Solar Radiation Intensity and System COP.  
Under different radiation intensities, the PVT system demonstrates higher power generation efficiency, with PVT panel power output increasing with radiation intensity from 78.33 W to 122.68 W, representing a 56.6% increase, significantly higher than that of PV panels. Additionally, the total electricity generation of the PVT panel exceeds that of the PV panel in all conditions, with an increase ranging from 8.7% to 8.3%. The theoretically calculated electrical efficiency is 19.84%, with measured relative increases of 1.19%, 3.65%, and 2.53%, validating its stability and performance advantages.
4. Linear fitting results show that the response of the PVT panel to radiation intensity is more sensitive, with intercepts and slopes of \(-\)33.79 and 0.3, respectively, superior to that of PV panels.
5. The performance of the direct-expansion solar PVT heat pump system is closely related to ambient temperature and solar radiation intensity. Under different conditions, the COP of the system exhibits significant variations. At an average ambient temperature of 16.94 \({}^{\circ}\)C, the system's COP increases by 5.67% compared to the average value, with radiation intensity and COP exceeding 194.44 W\(\cdot\)m\({}^{-2}\) and 0.14, respectively. COP shows a linear relationship with solar radiation, with slope differences of 0.00135 and 0.00088 W\(\cdot\)m\({}^{-2}\) under high and low temperatures, respectively.