Comprehensive review of green roof and photovoltaic-green roof systems for different climates to examine the energy-saving and indoor thermal comfort

Built-up regions are increasingly at risk from climate change and urban heat islands (UHIs). Solar panels and green roof systems (PV/GR) can provide several advantages to support ecologically sustainable cities. Research gaps in hot climates at the building and urban sizes are highlighted in this study, which examines the advantages of GR and combined PV/GR systems as well as their optimal design parameters. An extensive analysis of published works from the Scopus database was conducted to examine how energy-saving and indoor thermal comfort (UH-ES-ITC) was accomplished in urban structures, as well as the impact of green roofs (GR) and photovoltaic/GR systems on UHI mitigation. It's been found that, especially at building scale, GR and GR/PV systems enhance notable qualities in hot, dry locations. Sadly, not much research has been done on GR/PV systems on coupling scales. Among the research gaps identified in this study are those related to the methodology, scope, climate, objectives, variables, and features of this integration in different climate zones. Researchers and urban planners might use the findings to inform future research directions and implementation.