Coal Phase-Down and Cross-Fuel Risk in Peninsular Malaysia: System-Level Trade-Offs among Thermal Retention, Co-Firing and Renewable-Storage Deployment

Abstract Coal phase-down can lower power-sector emissions while shifting fuel-security exposure from coal to natural gas. This study quantifies that cross-fuel risk in Peninsular Malaysia using full-year hourly modelling in EnergyPLAN 16.22, MATLAB-based scenario automation and a controlled counterfactual that holds the wider national pathway constant while varying the treatment of an anonymised 1,600 MW Study Thermal Asset. The 2025 demand scale is externally checked against the Energy Commission’s recorded system peak, with a difference of 0.076%. Four cases are evaluated for 2030, 2035 and 2040: managed phase-down (PD), temporary retention (RET), retention with co-firing (RET-CF), and renewable-plus-storage deployment comprising 3,200 MW of solar PV and a 1,600 MW/6.4 GWh four-hour battery system (RE-ST). Relative to PD, RET reduces system natural-gas requirements by 9.35–12.45 TWh/yr but increases operational CO₂ emissions by 1.35–1.79 Mt/yr. A fuel-substitution ratio of 0.999–1.001 indicates near one-for-one coal-for-gas substitution on an input-energy basis. RET-CF preserves the gas reduction while moderating the emissions penalty. RE-ST changes the substitution mechanism more fundamentally, reducing both coal and gas use and lowering operational CO₂ emissions by 1.65–3.00 Mt/yr. It also lowers modelled annual system cost by USD 393–405 million under the adopted solar and battery cost assumptions. A 120-case sensitivity programme distinguishes the physical robustness of these effects from exposure to gas, carbon and substitute-fuel prices and retained-capacity availability. The results show that coal phase-down does not automatically reduce total fossil-fuel exposure: its resilience and decarbonisation outcomes depend on the portfolio that replaces the withdrawn coal contribution.