Hong Kong Polytechnic University and Peking University team: Global estimation of building-integrated photovoltaic potential combining 3D building and multi-source spatiotemporal datasets

A team from Professor Yan Jinyue of the Hong Kong Polytechnic University, in collaboration with the University of Tokyo and Peking University Shenzhen Graduate School, published an article titled "Global Estimation of Building-Integrated Facade and Rooftop Photovoltaic Potential by Integrating 3D Building Footprint and Spatio-Temporal Datasets" in Nexus, an interdisciplinary journal of Cell Press. The paper addresses the issue of assessing the potential of building-integrated photovoltaics (BIPV) in high-density urban environments. By integrating three-dimensional building footprints and multi-source meteorological spatiotemporal data and using advanced shadow simulation techniques to capture the dynamic shadow effects in urban environments, it achieves accurate estimation of the photovoltaic potential of building facades and rooftops, providing important support for urban planning and renewable energy utilization.

Research Background

In response to climate challenges, the Paris Agreement set a goal of limiting global warming to within 2 degrees Celsius. The International Energy Agency predicts that global renewable energy capacity will increase 2.7 times by 2030, but still below the target of tripling. Against this backdrop, distributed renewable energy systems have received more attention, and the deployment and installation of urban photovoltaic systems have been increasing. Traditional building-attached photovoltaics (BAPV) are gradually evolving into building-integrated photovoltaics (BIPV). In 2022, the BIPV market was valued at US\$19.82 billion, and it is expected to reach US\$89.8 billion by 2030, representing a 453% increase. In densely populated cities, the available surface area of building facades often exceeds the roof area, and facade photovoltaic panels provide an alternative for buildings with limited roof space. A comprehensive assessment of the photovoltaic potential of facades and rooftops is crucial for guiding urban design, supporting carbon-neutral pathway decisions, and promoting sustainable development.

 

Assessing urban photovoltaic potential faces many challenges, including complex and diverse building landscapes, temporal variations, geographical location, solar radiation, and shadow effects. Common methods rely on remote sensing technology and GIS data to identify areas suitable for photovoltaic module installation and analyze solar radiation. More advanced research has introduced classified building features, skyline analysis, and LiDAR technology for accurate calculation of solar radiation and detailed estimation of photovoltaic output. However, these methods have limitations in analyzing the shadow effects caused by the 3D building structures of cities, making it difficult to comprehensively assess photovoltaic potential.

 

In recent years, advances in GIS applications have reduced the difficulty of obtaining large-scale detailed urban building footprint data. Using high-resolution 3D building footprint data in conjunction with global meteorological databases provides an opportunity for a comprehensive assessment of BIPV potential. This study proposes an integrated solution that integrates multi-source 3D urban building footprint data and uses advanced shadow simulation technology to estimate photovoltaic potential from individual buildings to the global level. Based on this scheme, this study conducted an analysis in 120 cities worldwide, demonstrating the enormous energy potential of facade photovoltaics. In addition, this study developed an open-source toolkit called pybdshadow that can be easily integrated into existing geospatial analysis workflows. This solution provides important support for cities to achieve their carbon neutrality goals.

 

Core Content

1. Solar radiation estimation based on shadow projection

As shown in Figure 1, this study proposes a shadow simulation technology based on three-dimensional urban building footprint data to assess the potential of building-integrated photovoltaics (BIPV). By considering the solar altitude angle and azimuth angle, the shadow projection of a building at a specific time and location is calculated and decomposed into roof and facade shadow analysis. Using geometric projection formulas, the projection points of shadows on the target surface are accurately calculated, and by dynamic analysis of time intervals, solar radiation data on the building surface is obtained. This method can efficiently simulate urban shadow distribution and support photovoltaic potential assessment from individual buildings to the city scale, providing a technical basis for the design and optimization of BIPV systems.

 

Figure 1 Solar radiation calculation in a three-dimensional building environment

 

 

2. Global-scale building-integrated facade and rooftop photovoltaic potential estimation framework

As shown in Figure 2, this study proposes a global-scale framework for estimating the potential of building-integrated facade and rooftop photovoltaics. By integrating global three-dimensional building footprint data with meteorological data (including solar radiation, temperature, and wind speed), combined with shadow simulation technology, the solar irradiance of building facades and roofs is calculated. Using photovoltaic module parameters and weather data, the photovoltaic output of each building surface is estimated. This framework supports photovoltaic potential assessment from individual buildings to city blocks and even global city scales, providing a technical basis for optimizing photovoltaic system layout and configuration and contributing to sustainable urban development.

 

Figure 2 Global-scale framework for estimating the potential of building-integrated facade and rooftop photovoltaics

 

3. Verification and analysis of photovoltaic potential of individual buildings

This study verified and analyzed the photovoltaic potential of individual buildings by comparing measured photovoltaic output data. Taking 60 rooftop photovoltaic power stations on the campus of the Hong Kong University of Science and Technology as a case study, using measured photovoltaic power generation data and on-site weather data from open-source datasets, combined with building footprint data provided by Tencent Map, the shadow projection and photovoltaic potential of building facades and roofs were calculated. By comparing the model estimation results with measured data, the accuracy of the model in shadow simulation and photovoltaic output estimation was verified. As shown in Figure 3, the model can well reflect the changes in photovoltaic output under different seasons and weather conditions, providing reliable technical support for optimizing the configuration of building photovoltaic systems.

 

Figure 3 Verification and analysis of building-level photovoltaic potential by comparing with measured photovoltaic output data

 

 

4. Photovoltaic potential analysis of urban blocks

The study further investigated the photovoltaic potential of four different types of urban blocks in Hong Kong (high-rise, mid-rise, low-rise, and mixed-type buildings) and analyzed the impact of their three-dimensional spatial morphology on the power generation efficiency of building-integrated photovoltaics (BIPV), as shown in Figure 4. By calculating the daily photovoltaic output throughout the year, it was found that high-rise buildings, due to their high shadow coverage, had rooftop photovoltaic potential of only 83.16% of that of low-rise buildings, while the photovoltaic potential of building facades was relatively less affected by changes in urban morphology, mainly affected by building orientation and spatial layout. The study also showed that the photovoltaic potential of equator-facing facades is significantly higher than that of non-equator-facing facades. Optimizing urban building morphology and facade photovoltaic layout can significantly improve the overall photovoltaic potential and provide a more comprehensive strategy for urban renewable energy production.

 

Figure 4 BIPV potential of four types of three-dimensional urban spatial morphology

 

5. Comparative analysis of BIPV potential in the core areas of 120 cities worldwide

This study selects the core areas of 120 cities worldwide (20 from each continent) to assess their building-integrated photovoltaic (BIPV) potential, focusing on the impact of latitude, building morphology, and city size on photovoltaic efficiency. The study found that the rooftop photovoltaic potential in low-latitude regions is significantly higher than that in high-latitude regions, while the facade photovoltaic potential is relatively evenly distributed within the 40-degree latitude range. Although rooftop photovoltaic systems perform better in most areas, in cities with large facade areas, the facade photovoltaic potential averages 68.2% of the rooftop potential, exceeding it in some cities. The study also shows that Asian and North American cities have enormous photovoltaic application potential due to rapid economic development and high-density high-rise buildings, while African, South American, and Oceanian cities have high per-unit-area potential but lower potential for individual buildings. These findings provide important evidence for the promotion of photovoltaic technology and urban planning in different regions.

 

Figure 5 Comparative analysis of BIPV in the central areas of 120 global cities

Conclusions

This study proposes a method for estimating the photovoltaic potential of building facades and rooftops in three-dimensional urban morphology. By integrating building footprint models with multi-source meteorological data and simulating shadow projection on three-dimensional buildings, it enables the assessment of BIPV system energy output from individual buildings to a global scale. Covering 120 cities, the study analyzed the photovoltaic potential of specific buildings, building blocks, and 1-square-kilometer areas. It revealed that the facade photovoltaic potential is approximately 68.2% of the rooftop photovoltaic potential on average, exceeding 1.5 times in some urban areas. These findings highlight the enormous potential of building facades for photovoltaic installations and provide a technical basis for future research on the economic feasibility and market potential of facade-integrated photovoltaic systems. The study also shows that facade photovoltaic output is significantly affected by urban morphology and building orientation, providing valuable reference for urban planners, architects, and policymakers. Future research can further integrate microclimate data and detailed 3D models to explore the implementation potential, economic feasibility, and environmental benefits of BIPV systems, providing a comprehensive framework for sustainable urban development.

Research Team Introduction

 

The co-first authors are Dr. Yu Qing, postdoctoral researcher at Peking University Shenzhen Graduate School, and Mr. Dong Kechuan, graduate student at the University of Tokyo. Dr. Guo Zhilin and Professor Yan Jinyue, research assistant professor at the Hong Kong Polytechnic University, and researcher Zhang Haoran at Peking University Shenzhen Graduate School are the co-corresponding authors of this paper.

 

The International Urban Energy Research Center (UEX) is dedicated to addressing urban energy and related environmental issues and accelerating the achievement of carbon neutrality in cities. The research scope of this center covers urban energy science and technology, energy and new urban transportation modes, as well as interdisciplinary fields such as energy and artificial intelligence and data science.