Analysis of the Contribution of Vertical Façade Photovoltaic Applications to Rooftop PV Generation in Istanbul Using PVGIS Based Simulation

In Istanbul, where urban development is characterized by high-density vertical growth, a significant portion of the existing building stock is not well suited for rooftop solar photovoltaic (PV) installations due to limited roof area, architectural constraints, and structural limitations. In contrast, building façades represent a largely untapped resource for urban renewable energy generation, especially as the cost of PV technologies has declined substantially in recent years. This study aims to quantitatively assess the potential contribution of vertical façade-integrated PV systems to overall on-site energy production in the context of Istanbul, where tall and aging buildings dominate the urban landscape and usable rooftop surfaces are scarce. Using PVGIS-SARAH3 irradiance data, a three-year simulation (2021–2023) was conducted for the coordinates of Yıldız Technical University’s Davutpaşa Campus. Two configurations were analyzed: (i) a 1 kW rooftop PV system oriented horizontally at 0° tilt, and (ii) a 1 kW vertical PV system mounted at 90° tilt facing the South–Southwest direction (azimuth: 45°). A system loss factor of 14% was applied to both configurations, and hourly irradiance-derived power values were used to calculate daily, monthly, and annual energy production. The results show that vertical PV systems can achieve remarkably high annual performance under Istanbul’s climatic conditions, reaching 70.8% of the total annual production of the horizontal system. Over the three-year period, the horizontal installation produced 3572.2 kWh, while the vertical façade system produced 2530.4 kWh. Notably, during winter months when solar altitude is lower, the vertical system occasionally outperformed the horizontal configuration. These findings indicate that vertical PV installations can play a significant complementary role to rooftop PV, particularly during autumn and winter, thereby contributing to a more balanced annual production profile. Given Istanbul’s limited roof availability and high-rise urban fabric, these results provide strong technical motivation for incorporating façade-integrated PV into building energy strategies. In real applications, the ratio of rooftop to façade PV capacity will vary from building to building; thus, system design and investment decisions should be optimized according to architectural, orientational, and operational conditions. Future research may include long term experimental measurements at similar coordinates to validate simulation outcomes and extended simulations involving multi-aspect façade orientations. Such investigations would enable the development of a practical dataset for comparing real-world deviations from modeled performance.