Cooling photovoltaic surfaces with vertical or rooftop greenery: a review of mechanisms, key factors, methods and future research trends

Building-integrated photovoltaic (PV) systems and greenery are effective strategies for enhancing energy efficiency and ecological value in building façades and rooftops. Integrating PV with greenery not only provides environmental and urban-scale benefits but also helps reduce PV surface temperatures, mitigating efficiency losses caused by overheating. This review summarizes the cooling effects and efficiency improvements of two common systems: PV-green roofs (PV-GR) and façade-integrated PV-vertical greenery (FIPV-VG). Key influencing factors such as distance between PV and greenery, plant species, and climate zones are discussed. Experimental and simulation-based research methods are also outlined. Plant species used in previous literature and potential plant selection with high evapotranspiration rate are summarized and recommend, respectively. This article is a comprehensive critical literature review that synthesizes existing studies and does not collect or analyze primary data. FIPV-VG systems show surface temperature reductions of 1.65 °C to 4 °C and relative efficiency increases of 0.4 % to 3 %. PV-GR systems exhibit broader ranges, with cooling from 1 °C to 11 °C and relative efficiency gains between 0.08 % and 18 %. The temperate oceanic (Cfb) and tropical rainforest (Af) zones demonstrate the highest PV yield enhancements, ranging from 0.4 % to 17.1 % and 0.1 % to 8.6 %, respectively. Sedum is the most common used species in PV-GR while Thunbergia grandiflora is recommended for FIPV-VG due to its strong evapotranspiration capacity (6 L/day/m²) and vigorous growth. The optimal distance between PV panels and greenery requires further in-depth investigation, as it significantly influences both convective and latent heat transfer.