## 7 Future Research Directions  
Based on the current research results, future studies can be deepened based on the following directions:  
1. Optimization of flow channel design:  
The current study indicates the need for further optimization of the PVT backside flow channel design. Future research should focus on the combined effects of the geometric shape, size adjustments, and material selection of the flow channels on the thermal performance and electrical efficiency of the system. By using computational fluid dynamics (CFD) simulations and experimental validation methods, different design schemes can be compared to determine the optimal flow channel configuration. 2. Thermal stability analysis:  
This study shows that there are periodic fluctuations in the temperature of the PVT rear panel, which may affect the stability and long-term operating efficiency of the system. Therefore, future research should focus on developing high-precision thermal models to systematically evaluate the combined effects of ambient temperature, solar irradiation intensity, wind speed, and other factors. In addition, real-time dynamic control strategies to suppress temperature fluctuations can be explored to improve system reliability and lifetime. 3. System integration and energy efficiency improvement:  
Future research can explore the integration design with industrial hybrid heat pumps, investigating the synergistic optimization and integration strategies of the two systems, including the dynamic management and optimal configuration of energy flows to maximize energy efficiency. In addition, evaluating the economic and environmental benefits of such integrated systems in different application scenarios will be an important aspect of future research. In-depth exploration of these research directions can be expected to provide scientific evidence and technical support for the design and application of PVT systems, thereby promoting the advancement and application of renewable energy technologies. D.Z. : conceptualization, investigation, validation, funding acquisition, project administration, writing--review and editing; Y.Z. : conceptualization, methodology, data curation, software, investigation, validation; formal analysis, visualization, writing--original draft, writing--review and editing; Z.Y. : investigation, formal analysis, supervision, resources; T.M. : conceptualization, methodology, formal analysis, funding acquisition, resources, writing--review and editing;  
[PERSON]; [PERSON] [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON] Performance Analysis of a Direct-Expansion Solar-Assisted Heat Pump Using a Photovoltaic/Thermal System for Water Heating. In Proceedings of the Smart Technologies, Systems and Applications: First International Conference, Smart-Tech-IC 2019, Quito, Ecuador, 2-4 December 2019; Proceedings 1. Springer International Publishing: Cham, Switzerland, 2020. * [PERSON] et al. (2020) [PERSON]; [PERSON]; [PERSON]; [PERSON] Theoretical analysis on efficiency factor of direct expansion PVT module for heat pump application. _Sol. Energy_**2020**, _206_, 677-694. [CrossRef]
* [PERSON] and [PERSON] (2017) [PERSON]; [PERSON] Theoretical analysis on a new direct expansion solar assisted ejector-compression heat pump cycle for water heater. _Sol. Energy_**2017**, _142_, 299-307. [CrossRef]
* [PERSON] et al. (2020) [PERSON]; [PERSON]; [PERSON]; [PERSON] Performance analysis of solar assisted heat pump coupled with build-in PCM heat storage based on PV/T panel. _Sol. Energy_**2020**, _197_, 279-291. [CrossRef]
* [PERSON] et al. (2018) [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON] Experimental performance analysis of a direct-expansion solar-assisted heat pump water heater with R134a in summer. _Int. J. Refrig._**2018**, _91_, 12-19. [CrossRef]
* [PERSON] et al. (2018) [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON] A variable frequency control method and experiments of a direct-expansion solar-assisted heat pump system. _Sol. Energy_**2018**, _176_, 572-580. [CrossRef]
* [PERSON] et al.