Power systems with increasing shares of wind and solar are experiencing greater intra-day variability, ramping requirements and dependence on flexible resources. Tamil Nadu provides a relevant operational testbed because of its large renewable portfolio, significant industrial Open Access participation and rapidly growing solar utilisation. Its textile, automotive and other C&I sectors increasingly procure renewable energy through captive and Open Access arrangements, while emerging EV charging and data-centre loads add further flexibility requirements. This paper presents a data-driven assessment of solar photovoltaic–battery energy storage system (PV–BESS) integration under 15-minute scheduling, incorporating time-of-day tariffs, deviation exposure, network-loss treatment and Open Access energy accounting. Utility-derived records from two operating PV–BESS installations examine surplus daytime solar storage, measured BESS discharge and subsequent consumer adjustment. By shifting solar energy to the 18:00–22:00 evening peak, BESS can reduce grid imports when applicable C&I tariffs carry a 25% premium. A scheduling framework incorporating state-of-charge, charging/discharging limits, losses, tariffs and deviation costs is formulated to improve net deliverable energy and reduce peak-period dependence. The study also discusses voltage support, fast frequency response and future grid-forming functionality.