## 4 Processing of Experimental Data
### Electricity Generation of PVT and PV Panels in Relation to Solar Radiation  
The significance of the electricity generation of PVT panels is that it directly reflects the overall performance of the direct-expansion solar PVT heat pump system and visually represents the energy-saving effects of the system. This is crucial for assessing the sustainability and efficiency improvements of the system during its operation. As shown in Figure 9, through comprehensive data analysis across 4 days under different weather conditions, the electricity generation gradually increases with the increase in radiation intensity, reaching a peak and then stabilizing, followed by a decrease as the radiation weakens. Under conditions with average temperatures of 16 \(\pm\) 0.5 \({}^{\circ}\)C and average radiation intensities of 369 W\(\cdot\)m\({}^{-2}\) (overcast), 483 W\(\cdot\)m\({}^{-2}\) (cloudy), and 510 W\(\cdot\)m\({}^{-2}\) (sunny), the average instantaneous electricity generation of the PVT panels is 78.33 W, 109.83 W, and 122.67 W, respectively. Data analysis indicates a significant positive correlation between the average electricity generation of the PVT panels and solar radiation intensity. As the radiation intensity increases, the electricity generation increases, but the rate of increase gradually slows down, and the system's response to the increase in radiation tends to saturate. Figure 8: Impact of Solar Radiation Intensity on PVT and PV Panel Temperatures. Under similar environmental temperatures, with the radiation intensity increasing from 369 W\(\cdot\)m\({}^{-2}\) to 510 W\(\cdot\)m\({}^{-2}\), the instantaneous electricity generation of the PVT panels increases from 78.33 W to 122.68 W, representing a 56.6% increase. This change reflects that under higher solar radiation intensity, the PVT panels absorb more energy, thereby increasing the system's electricity generation. Throughout the entire operational period, the total electricity generation of the PVT panels is significantly higher than that of the PV panels, as shown by the time integration analysis from 8:00 to 17:30 (see Figure 10). Under average temperatures of 16 \(\pm\) 0.5 \({}^{\circ}\)C and different radiation intensities, the total electricity generation of the PVT panels is 0.75 kWh, 1.04 kWh, and 1.17 kWh, respectively, while that of the PV panels is 0.69 kWh, 0.98 kWh, and 1.08 kWh, respectively. Detailed experimental data can be found in Table 4.  
Under overcast, cloudy, and sunny conditions, the total electricity generation of the PVT panels relative to the PV panels increases by 8.7%, 6.1%, and 8.3%, respectively. The data indicate that in the direct-expansion solar PVT heat pump system, the PVT panels exhibit higher electricity generation under different conditions, especially during the transition from overcast to sunny conditions, where the performance of the PVT panels in electricity generation relative to the PV panels is significantly enhanced. This further confirms the excellent performance of the PVT system in utilizing solar energy. To provide a more intuitive comparison of the relationship between the instantaneous electricity generation of PVT and PV panels and solar radiation intensity, linear fitting was performed in this study, and the data for average solar radiation intensity and average instantaneous electricity generation under various conditions were obtained (with goodness of fit greater than 0.99). The fitting results show that the intercept and slope of the instantaneous electricity generation curve for PVT panels are \(-\)33.79 \(\pm\) 11.07 and 0.3 \(\pm\) 0.02, respectively, while those for PV panels are \(-\)31.18 \(\pm\) 9.46 W and 0.28 \(\pm\) 0.02, respectively. The functional relationships between solar radiation intensity and average instantaneous electricity generation obtained are as follows(As shown in Figure 11):  
\[\text{Y}_{PVT}=0.3\text{X}-33.79\]