Enviro-Economic Assessment of Vegetation–PV Envelope Retrofits for Nearly Zero Energy Buildings in Hot-Humid Climates

The growing demand for sustainable energy solutions in the built environment has increased interest in hybrid envelope retrofits that integrate vegetation systems with on-site photovoltaics (PVs). This study presents a comparative assessment of two integrated vegetation–PV envelope retrofit strategies for an educational building in a cooling-dominated hot-humid climate relevant to Nearly Zero Energy Building (NZEB) applications. A calibrated dynamic simulation model was developed to quantify annual net electricity savings, operational CO 2 emission reductions, and cost-effectiveness using the levelized cost of saved electricity (LCOS). Two configurations were assessed: a solar green roof and a façade system combining green walls with glazing-integrated photovoltaics (GIPVs), enabling a consistent evaluation of roof-based and façade-based hybrid systems under identical conditions. Both strategies deliver comparable energy and environmental performance. The solar green roof achieves annual net electricity savings of 231.0 MWh and avoids 163.3 tCO 2 , while the green walls–GIPV system provides 228.3 MWh and 161.4 tCO 2 . However, significant differences are observed in economic performance. The LCOS of the solar green roof is approximately 0.07 $/kWh, compared with 0.28 $/kWh for the façade-integrated system. The results demonstrate that vegetation–PV hybrid retrofits can effectively support NZEB pathways in hot-humid climates, while highlighting that the solar green roof provides a more cost-effective solution under the studied conditions. The study contributes a consistent, decision-oriented comparison of integrated vegetation–PV strategies, linking energy, environmental, and economic performance within a unified modeling framework.