Global Estimation of Building-Integrated Facade and Rooftop Photovoltaic Potential by Integrating 3D Building Footprint and Spatio-Temporal Datasets

TL;DR

This study presents a global framework for estimating Building-Integrated Photovoltaics (BIPV) on facades and rooftops by integrating 3D building footprints with multi-source meteorological data. It employs shadow casting to compute time-resolved solar insolation on building surfaces and uses pvlib to translate irradiance into PV outputs, with facade PV efficiency set at 68% of rooftop performance. Validations at the building scale (HKUST) and block level in Hong Kong, plus a global city analysis of 120 cities, reveal that facade PV potential averages about 68.2% of rooftop potential, with 17.5% of samples where facade PV surpasses rooftop PV. The work provides an open-source toolkit (pybdshadow) and a scalable methodology for rapid, high-resolution BIPV potential mapping to guide urban design and policy toward greater deployment of facade-based solar energy.

Abstract

This research tackles the challenges of estimating Building-Integrated Photovoltaics (BIPV) potential across various temporal and spatial scales, accounting for different geographical climates and urban morphology. We introduce a holistic methodology for evaluating BIPV potential, integrating 3D building footprint models with diverse meteorological data sources to account for dynamic shadow effects. The approach enables the assessment of PV potential on facades and rooftops at different levels-individual buildings, urban blocks, and cities globally. Through an analysis of 120 typical cities, we highlight the importance of 3D building forms, cityscape morphology, and geographic positioning in measuring BIPV potential at various levels. In particular, our simulation study reveals that among cities with optimal facade PV performance, the average ratio of facade PV potential to rooftop PV potential is approximately 68.2%. Additionally, approximately 17.5% of the analyzed samples demonstrate even higher facade PV potentials compared to rooftop installations. This finding underscores the strategic value of incorporating facade PV applications into urban sustainable energy systems.

Figures (5)

• Figure 1: Computation of solar insolation within 3D architectural contexts.a Shows the geometry relationship of a wall with its projection on the ground in a sun position. b illustrating the geometric relationship in which Building A casts a shadow over the roof of Building B. c depicts how Wall B casts a shadow onto Wall A. d shows how to represent and estimate the detailed solar insolation time on the building roof and facade in a period by overlaying the building shadows, this will generate a number of smaller polygons on each building. e gives an example showing the estimation results of ground, facade and roof shadows for a city block at a given time. f and g visualize the daily solar insolation time of this city block on January 1, 2022, in both the roof and 3D views. h shows an example of solar insolation time for 23,904 buildings in Shenzhen, China, as of January 1, 2022.
• Figure 2: Global-scale building-integrated facade and rooftop PV potential estimation framework. By integrating building footprint data with global solar data, the model estimates rooftop and facade solar irradiance first. Then, it uses PV module parameters and weather data to estimate the PV output for each building surface. The model framework enables the estimation of PV potential at the building surface level for individual buildings and can be further extended to the estimation of PV potential of urban blocks on a global city scale.
• Figure 3: Validation and analysis of building-level PV potential by comparing with measured PV output dataa shows the comparison of the satellite image and the shadow casting estimated by building footprint at the same timestamp. b compares the rooftop daily measured PV output with the estimated PV potential for two selected buildings, SQ1 and UG3. c presents the satellite image and the building footprint data for the two buildings. d shows the shadow cast over the case region at different times in 2023-12-11, where the roof of building SQ1 is not blocked by shadows during the day, while the roof of building UG3 is blocked by the shadow of the adjacent building at around 17:30 in the afternoon. e compare the measured rooftop PV output with the estimated rooftop PV potential of the building SQ1 and UG3, where we can clearly see that the power generation efficiency of UG3 during the afternoon hours of 16:00-18:00 is significantly lower than that of SQ1, and this trend is well reflected in our estimated result.
• Figure 4: BIPV potential of four types of 3D urban spatial morphology in Hong Konga Illustrates the four categories of city blocks, each characterized by a unique 3D spatial configuration, accompanied by an estimation of their respective PV potential on building roofs and facades. b and c provide detailed insights into the shadow coverage ratio affecting both the facades and rooftops across these diverse city blocks. d and e show the estimated roof and facade-integrated PV potential, with shadow casting between the buildings considered. In e, the solid lines represent facades oriented towards the equator, while the dashed lines indicate facades not oriented towards the equator. f provides a comparative analysis of the daily average PV power generation per building across the four city blocks, assuming that all available facade and rooftop surfaces are equipped with PV panels.
• Figure 5: Comparative analysis of BIPV in central urban areas of 120 global cities. The proposed methodology has been implemented across urban centers in 120 typical cities worldwide, each featuring a 1 km $\times$ 1 km area for the assessment of BIPV potential. a shows the estimated Plane of Array Irradiance (POA) of both roof and facade in the 120 cities, each figure uses color to represent rooftop PV and marker size to represent facade-integrated PV. b depicts the average daily PV potential in kWh per building, while c displays the daily PV potential per unit of area. d presents a scatter plot illustrating the PV potential of 120 cities across various continents.