Mitigating firm-capacity delay risk through stochastic planning of flexible generation and battery storage

Abstract

Energy-transition plans often assume that committed firm-capacity projects are commissioned on schedule, yet delayed delivery can create temporary adequacy risks and require additional mitigation resources. This study develops a scenario-based stochastic adequacy-mitigation model to quantify the system-level impacts of firm-capacity delay risk in the Jawa–Bali power system over the 2025–2034 planning horizon. The model co-optimizes flexible gas engines, photovoltaic battery energy storage systems, and standalone battery energy storage systems while considering reserve-margin requirements, capacity credit, representative hourly operation, storage charging and discharging, and unit commitment constraints. The results show that the on-time national-planning pathway remains adequate without additional endogenous mitigation. However, delay-risk cases require substantial mitigation capacity. The moderate-delay case selects 4.00 GW of gas engines and 3.00 GW of photovoltaic battery energy storage systems, increasing expected system cost by USD 3.80 billion. The severe-delay case increases gas engine capacity to 5.70 GW while maintaining 3.00 GW of photovoltaic battery energy storage systems, raising expected cost by USD 5.25 billion. These findings show that firm-capacity delay risk should be explicitly incorporated into long-term energy-transition planning to avoid underestimating adequacy needs, mitigation investment, and system-cost exposure.