This paper presents a single-site empirical case study — formulated without claims to statistical generalisability — of a 10 kWp photovoltaic (PV) system coupled with a 19.2 kWh lithium iron phosphate (LiFePO₄) battery storage unit, based on 365 days of operational data from a single-family household in southern Poland (50.06°N; 19.94°E). The system was commissioned in August 2024; the battery was pre-charged to approximately 80% SOC prior to the monitoring period commencing 1 September 2024, ensuring that the initial SOC condition is documented and that the annual energy balance closes with negligible net change in stored energy. Standard-ised performance indicators — Self-Consumption Rate (SCR), Self-Sufficiency Rate (SSR), Equivalent Full Cycles per Year (EFC/year), and Grid Dependency Index (GDI) — are deter-mined at daily and monthly resolution. Measured annual PV yield (882.7 kWh/kWp) is com-pared with PVGIS TMY reference data (915.4 kWh/kWp), confirming that the monitoring period was characterised by irradiation approximately 3.6% below the long-term mean. The system achieved annual SCR = 46.2% and SSR = 80.9%, with complete grid independence on 70.1% of days. Battery round-trip efficiency of 91.1% confirms technical quality, while EFC ≈ 96.6 cy-cles/year indicates significant underutilisation of cycling capacity relative to the rated 6,000-cycle lifetime. Economic analysis indicates a battery-specific simple payback period of approximately 26–32 years (sensitivity range) under current Polish net-billing tariffs, identifying uncontrolled electric vehicle (EV) charging as the principal disruptor of system balance. The results constitute empirical evidence relevant for validating simulation models and provide observations useful for the design of residential energy storage systems in continental European climates.