Experimental Study on the Impact of Shallow Substrate Green Roof Integrated Photovoltaic Systems on the Surrounding Microclimate

Climate change has intensified the urban heat island effect. In line with the targets set at COP28, Taiwan aims to increase renewable energy generation to 27–30% by 2030, with approximately 50% from solar photovoltaic (PV) systems. In the densely built Taipei metropolitan area, rooftop PV installations have been widely promoted. However, while PV panels convert solar radiation into electricity, they also influence the surrounding thermal environment. Shallow substrate green roof systems are known to reduce rooftop temperatures, and their integration with PV panels requires further examination regarding thermal interaction and microclimate regulation.This study was conducted on the seventh-floor rooftop of the Integrated Technology Complex Building at National Taipei University of Technology (25.0443° N, 121.5354° E). Field measurements were collected daily from 09:00 to 17:00 between October 1 and October 17, 2025. Three rooftop types were evaluated: (1) shallow green roof-integrated PV panels, (2) conventional rooftop PV panels, and (3) bare concrete roof surfaces. Air temperature and relative humidity were analyzed to assess microclimatic effects.Results show that the shallow green roof-integrated PV system reduced temperature by up to 1.5°C (3.9%) compared to conventional PV panels. Heat accumulation beneath conventional PV panels increased adjacent concrete temperatures by 4.3%. With irrigation, the green-integrated system reduced temperature by up to 4.2°C (10.2%) compared to the concrete roof. It also showed an earlier afternoon recovery in relative humidity (9.7%), accelerating surface cooling.Overall, shallow green roof-integrated PV systems mitigate PV waste heat through evapotranspiration and moisture-driven cooling, creating a localized micro-cooling effect. Ventilation conditions significantly influence heat accumulation and should be considered in design applications.