Photovoltaic systems as a pathway to energy efficiency in multi-apartment buildings

Building renovations and rooftop photovoltaics (PV) each offer potential energy savings, but their combined effect in urban multi-apartment buildings is not well understood. This study addresses this gap by evaluating both measures together. Using data from 10 renovated apartment buildings and simulating rooftop PV installations, we quantify technical energy savings, reductions in CO 2 emissions, and economic feasibility under current policy support. In the case-study buildings, envelope retrofits yield an average 50 % cut in heating energy demand, but the investment payback exceeds 80 years even with a 40 % subsidy, limiting their standalone viability. In contrast, rooftop PV systems can cover up to 57 % of a building’s electricity demand, reduce CO 2 emissions by over 4 t CO 2 per year, and achieve a payback of roughly 7 years with an internal rate of return above 13 %. Combined, these measures significantly improve the building’s energy and carbon profile, although PV systems yield the most immediate financial and environmental benefits. As part of the study, a replicable methodology was developed that integrates rooftop PV potential assessment with building-specific energy models and architectural constraints. Combined with Latvia’s 2024 enhancements to citizen-energy-community regulations, our findings indicate that rooftop PV on multi-apartment blocks is a cost-effective pathway to urban decarbonization. These results can guide policymakers and stakeholders in optimizing investments in building refurbishment and solar deployment to achieve energy efficiency goals. • Renovations reduce heating energy use in apartment buildings by 50 % on average. • Renovation face significant financial obstacles, with payback periods > 80 years. • Rooftop PVs pay back in 7 years, cut CO2 by 4 tons annually, and cover ∼57 % of power needs. • Renovation + PV systems boosts efficiency, cuts costs, and supports sustainable urban living. • Strong policy, public support, and funding are key to meeting EU 2050 climate goals.