Distinct Contributions of Building-Integrated PV and BESS to Energy and Cost Reduction Using Measured Operational Data

Despite the widespread deployment of combined PV–BESS systems in community buildings, the distinct contributions of each technology to energy consumption reduction and electricity cost savings remain poorly quantified under real operational conditions. Three years of measured hourly operational data (2023–2025) from a twelve-building mixed-use complex in Siheung-si, South Korea, were analyzed to disaggregate the contributions of a 105.84 kW PV array and a 216 kWh BESS operating under a time-of-use (TOU) electricity tariff. PV and BESS contributions were separated by computing hourly energy flows from measured generation, charging, and discharging data. PV self-consumption accounted for all energy savings, totaling 270,028 kWh over the study period, while the BESS recorded a net energy loss of −7833 kWh due to round-trip efficiency losses. In contrast, the BESS contributed to electricity cost reduction by shifting on-peak consumption to off-peak charging periods, accounting for 13–15% of total annual cost savings. Total electricity cost reduction over three years reached $31,020, with on-peak periods contributing 70.3% of savings. These results establish that PV and BESS serve fundamentally distinct functions: PV reduces both energy consumption and electricity costs through direct self-consumption, while BESS operates as a cost-shifting mechanism through TOU arbitrage without reducing net energy use. The quantitative results provide a practical basis for evaluating PV–BESS systems in community-scale buildings under real-world tariff conditions.