PVIGR series: Experimental insights into PV rooftops and urban heat

Intro:
While large-scale rooftop photovoltaics (PV) are central to low-carbon urban transitions, their local thermal impacts remain poorly understood due to limited experimental evidence. To address this gap, our team conducted a large-scale field experiment on multiple 200 m² rooftops in subtropical Hong Kong, comparing bare roofs, PV roofs, and PV-integrated green roofs (PVIGRs). Together, these three studies tell a broader story: rooftop PV is not thermally neutral; PVIGR can serve as a climate-adaptive design strategy, but its benefits depend strongly on system configuration; and the value of rooftop PV should be assessed not only by electricity generation, but also by its implications for building cooling demand and heat resilience. This work has been featured in PV Magazine. An overview of the PVIGR studies is available here: PVIGR_Slides (PDF)

References:

[1] Chen, L., Lin, Z., Zhou, Q, Zhang, S., Li, M., Wang, Z. (2025). Impacts of photovoltaics and integrated green roofs on urban climate: Experimental insights for urban land surface modelling, Renewable and Sustainable Energy Reviews, 217 (2025) 115709. DOI: https://doi.org/10.1016/j.rser.2025.115709

[2] Chen, L., Chang, H., Zhang, S., Li, M., Li, L., Karamanis, D., & Wang, Z. (2026). Comparing Designs for Photovoltaic-Green Roofs: A Year-Long Field Study in a Subtropical Climate. Renewable Energy, 125805. DOI: https://doi.org/10.1016/j.renene.2026.125805

[3] Chen, L., Zhang, S., Cheng, I., Chang, H., Chen, F., Li, M., & Wang, Z. (2025). The Resilience Paradox of Rooftop PV: Building Cooling Penalties and Heat Risks. Building and Environment, 113233. DOI: https://doi.org/10.1016/j.buildenv.2025.113233

Key Findings:

• PV heat island effect: PV roofs elevated local air temperatures by more than 4 °C on sunny days.

• PVIGR as a climate-adaptive design: PVIGRs did not produce a clear cooling effect above the panels, but they reduced canopy temperatures beneath the panels and improved annual noontime power output by up to 3.7% under well-designed configurations, highlighting the importance of balancing vegetation-driven cooling against shading and restricted airflow.

These studies show that rooftop PV should be understood as an integrated climate–energy system rather than an electricity-only technology. They highlight the need for climate-adaptive PV designs that jointly consider power generation, local thermal effects, building energy demand, and urban heat resilience.

Our work has also been featured in PV Magazine and LinkedIn.