Data-Driven Assessment of Solar Surplus and Battery Storage for Cost and Emission Reduction in Sri Lanka’s Power System

Rapid growth in solar photovoltaic deployment across the Global South is increasingly constrained by temporal mismatches between generation and demand, resulting in renewable curtailment, inefficient system operation, and continued reliance on oil-based peaking generation. Grid-scale battery energy storage systems (BESS) are widely recognised as a key enabler of renewable integration; however, empirically grounded assessments of their operational and developmental value remain limited in emerging power systems. This study develops a high-resolution, data-driven analytical framework to quantify solar-excess availability and derive indicative battery-storage requirements for Sri Lanka’s national power system. Using 15-minute operational, irradiance, generation, and cost datasets obtained from national regulatory and system-planning institutions, the analysis integrates solar-generation potential modelling, solar-excess identification, and storage-dispatch simulation to evaluate feasible charge-discharge windows and system-level impacts. Results show that existing solar deployment already produces substantial and recurrent midday surplus energy concentrated within consistent 2-4-hour windows. Percentile-based sizing indicates that short-duration, grid-scale storage on the order of several hundred megawatts, with energy capacities of a few gigawatt-hours, is technically sufficient to capture the majority of daily solar surplus while displacing high-cost thermal generation during evening peak periods. The findings demonstrate that appropriately sized battery storage can enhance solar utilisation, reduce operating costs and emissions, and improve grid flexibility without requiring long-duration storage solutions. Beyond system-level efficiency gains, the results highlight the role of battery storage as a strategic enabler of energy security, affordability, and resilient low-carbon transitions in fuel-import-dependent power systems across the Global South.