## 5 Conclusions  
This study proposes an optimization strategy for installing PV systems above the main transformer room of semi-outdoor substations, aiming to enhance natural ventilation for both the main transformer room and the PV panels while also comparing the power generation performance of various PV configurations. Through in-depth analysis, this study evaluates the effects of adjusting roof form, slope angle, and windward orientation on improving both the natural ventilation performance of the main transformer room and the power generation capacity of the rooftop PV system. The horizontally arranged PV system yields the best photovoltaic performance and has minimal impact on the wind environment inside the main transformer room. However, the installation of horizontal PV systems reduces airflow velocity in ventilation zones, particularly in the windward bottom area, where the ventilation speed is decreased by 13.2% and by 11.8% in the leeward condition. Additionally, under leeward conditions, horizontal PV systems have a negative effect on heat dissipation in the main transformer room and offer poor ventilation conditions for cooling the rear surface of the PV modules. For unilateral pitched PV systems, since Guangzhou is located in the Northern Hemisphere, south-facing installations are more favorable for power generation. Compared to horizontal PV systems, the energy losses are smaller: at tilt angles of 5\({}^{\circ}\) and 10\({}^{\circ}\), the south-facing single-slope configurations generate power outputs of 118.3 MWh (1.74% loss) and 115.7 MWh (3.90% loss), respectively. However, for north-facing systems with the same tilt angles, the effect of self-shading becomes particularly significant; at 10\({}^{\circ}\), the loss rate reaches 20.02%, making it the least favorable option for PV generation. Therefore, north-facing configurations are not recommended. In terms of natural ventilation, when the PV system is oriented windward, it can improve the airflow inside the main transformer room, reduce stagnant zones, and guide the inlet airflow toward the center of the room. Compared to horizontal PV systems, the proposed PV layouts in this study significantly improve ventilation performance, with increases of 12.6% (Case 5), 11.3% (Case 6), 11.9% (Case 9), and 13.2% (Case 10). Compared to the no-PV baseline (Case 1), these configurations also demonstrate good ventilation, with minor airflow losses of 2.3%, 3.4%, 2.9%, and 1.7%, respectively, ensuring adequate ventilation for the transformer room. Additionally, these layouts offer better airflow beneath the PV panels, aiding module cooling. Larger tilt angles (10\({}^{\circ}\)) have a more pronounced effect on indoor airflow than smaller angles (5\({}^{\circ}\)), but they also result in higher power losses, especially for north-facing installations. Inleeward configurations, PV systems can negatively impact ventilation in the transformer room and are subjected to higher wind loads; the steeper the angle, the greater the wind pressure, which increases structural requirements for mounting the PV system. Therefore, careful consideration is needed when choosing a single-slope orientation, particularly in controlling the overall tilt angle. For symmetrical pitched PV systems, good ventilation conditions are maintained under both windward and leeward conditions. Compared to horizontal PV systems, symmetrical layouts significantly improve ventilation by 8.6% (5\({}^{\circ}\)) and 14.6% (10\({}^{\circ}\)). Ventilation performance improves with increasing tilt angle, with the 10\({}^{\circ}\) symmetrical layout achieving the best ventilation performance among all PV-equipped cases--only a 0.6% reduction compared to the no-PV baseline. However, due to self-shading, power generation is reduced by 11.88% (5\({}^{\circ}\)) and 13.87% (10\({}^{\circ}\)), with losses increasing at steeper angles. When the transformer room is on the windward side, the PV system improves indoor airflow; on the leeward side, the impact is minimal.