Improving solar gains in GIS-based urban building energy modeling for energy poverty assessment

In Europe, a large share of the building stock is old, with approximately 85% of buildings constructed before the 1970s and 64% exhibiting poor energy performance. Achieving the decarbonization of the building sector by 2050 requires comprehensive and socially inclusive energy efficiency strategies. The revised Energy Performance of Buildings Directive strengthens energy efficiency requirements while explicitly addressing energy poverty, particularly by protecting vulnerable households from excessive rent increases following renovations. This study proposes a multidimensional framework that integrates Urban Building Energy Modeling with socio-economic analysis to evaluate energy retrofit scenarios and their impacts on energy poverty in the city of Turin, Italy. A physics-based UBEM was calibrated using hourly heating consumption data from 125 residential buildings and further enhanced through Machine Learning to extend predictions across multiple retrofit configurations. To improve the representation of boundary conditions in physics-based models, a simplified QGIS-based solar gains simulator was developed to estimate solar irradiation on roofs and façades using 2.5D building footprints enriched with height, orientation, and shading information. Solar gains are calculated separately for horizontal and vertical building components, explicitly accounting for urban shading effects and sky view factors. The solar model validation demonstrated a good agreement with measured solar radiation data on horizontal surfaces and CitySim Pro simulation on vertical envelopes with MAPE of 2%–3% and 6%–23%, respectively. Energy poverty was assessed using two widely adopted indicators: the 10% income threshold and the Low Income High Cost indicator. Results indicate that wall insulation is the most effective single retrofit measure, reducing energy poverty levels from a baseline of 14.4%–17.6% to approximately 6.3%. On the other hand, a fully incentivized global retrofit can reduce the energy poverty index to as low as 2.2%. However, the current annual renovation rate of around 2% significantly constrains the large-scale impact of these interventions.