Large-scale analysis of photovoltaic, photovoltaic-thermal, and solar thermal systems in high-density urban environments

Urban solar energy deployment in high-density environments is often limited by rooftop availability, building height, and shading. This study presents a robust, data-driven framework integrating high-resolution Geographic Information System data, 3D building models, and detailed urban morphology to evaluate the potential of various solar technologies, including standard photovoltaic systems, photovoltaic-thermal (PVT) systems (e.g., using water, air, or refrigerant as heat transfer media), and solar thermal systems (e.g., flat-plate or evacuated tube collectors with water or air). Using Hong Kong as a case study, the analysis highlights the impact of urban geometry, showing that incorporating shading reduces rooftop solar radiation by 31 %. Among the technologies assessed, photovoltaic-thermal systems demonstrate the highest combined energy yield, generating approximately 15.99 TWh per year (electricity and heat) from 40 % rooftop utilization. Of this, electricity accounts for 4.0 TWh/year—about 8.9 % of Hong Kong's total electricity consumption (44.8 TWh in 2022), which comprises 33 % of its final energy use. In the residential sector, cooling and hot water each account for 25–26 % of energy demand, emphasizing the value of combined thermal and electrical outputs. Thermal results represent theoretical maximums, as building-specific thermal demands were not modelled. This deployment could offset up to 30.8% of current energy imports, lower NOₓ emissions by 44.3%, and decrease smog-forming pollutants by 8.6%. The proposed framework offers a scalable, transferable approach to urban energy planning, enabling cities worldwide to harness rooftop solar energy more effectively for sustainability and climate resilience.