Solar potential in the extension of old residential communities based on Inter-Building Effects: a case study of Nanjing

In the micro-renewal of aging urban residential community, inter-building effects (IBE) significantly influence solar potential, thereby affecting energy efficiency and environmental quality. This study systematically investigates the relationship between building extensions and solar potential. Using Nanjing as a case study, clustering algorithms were employed to classify fundamental building typologies, and Ladybug Tools were utilized to conduct solar radiation simulations across 360 cases. The findings reveal a strong negative correlation between floor area ratio (FAR) and solar potential, with enclosed building layouts experiencing the most pronounced reduction in total annual solar radiation (correlation coefficient: -0.82). Among the IBE indicators, the sky view factor (SVF) and vertical sky view factor (SVFv) exhibit the strongest positive correlations with solar potential (both exceeding 0.9), while height-to-width ratio (H/W) and height difference (DifH) demonstrate the strongest negative correlations (approximately -0.88). Furthermore, for buildings of the same typology, greater initial height mitigates the impact of extensions on solar potential. For point blocks, expansion decreases solar power potential (SPP) from 22.43% at 1F to 4.66% at 7F. A gradient extension strategy proves to be the optimal approach, with the recommended extension scheme involving one-floor, three floors, and five floors extensions concentrically surrounding the target building. These insights provide a robust foundation for optimizing solar access in sustainable micro-renewal projects for aging residential communities.