Impact of electrical energy storage on the performance of photovoltaic systems in building retrofits

• EES effects studied in retrofitted buildings with max rooftop PV and R290 based HP. • Energy and economic benefits assessed through dynamic simulations. • New index quantifies the potential of EES to mitigate PV-related grid disturbances. • Residential EES achieves positive NPV; tertiary unprofitable in current conditions. • EES integration with PV supports zero-emission targets in residential and tertiary. This study investigates the impact of integrating electrical energy storage (EES) into photovoltaic (PV) systems serving existing buildings that have already undergone energy retrofitting. Focusing on representative locations in Southern Europe, the analysis considers both residential and tertiary buildings with typical configurations. The buildings are assumed to have maximum rooftop PV coverage and are equipped with heat pumps using low-GWP R290 refrigerant, in line with recent regulations. Dynamic simulations were carried out to assess the benefits of varying storage capacities, with particular attention to both energy performance and economic feasibility. To achieve the target of zero-emission buildings (ZEBs), the renewable share of the energy supplied from the grid was also taken into account. Furthermore, a new index was introduced to quantify the ability of EES to mitigate grid disturbances caused by PV generation. The Discounted Cash Flow (DCF) method was applied to determine the optimal storage sizes. Results show that, in residential buildings, storage sized according to a 10-year Net Present Value (NPV) criterion provides positive returns, with peak energy performance reached below the economic break-even point. Conversely, for the tertiary sector, the investment is not economically viable under current conditions, mainly due to daytime-concentrated electricity use, which reduces storage benefits, and lower electricity purchase costs, which limit the advantage of self-consumption. Nonetheless, storage still improves key energy performance indicators. In some cases, EES integration enables the PV system to cover 100% of annual electricity demand. The integration of EES also leads to a reduction in grid disturbance of up to 61.2%. Overall, the study confirms that appropriately sized EES can significantly enhance self-consumption, reduce grid disturbances, and support buildings in approaching net-zero emission targets.