Evaluating the substitution of coal-fired power plants with renewable energy and multi-temporal energy storage for decarbonization

• Significant regional heterogeneity is observed in the substitution effects. • The dominant flexibility resources in power systems vary across transition phases. • Increased extreme weather events imply stronger reliance on long-duration energy storage. • A temporal decoupling algorithm is designed to facilitate long-duration energy storage integration. Replacing coal-fired power plants (CFPPs) with variable renewable energy (VRE) and energy storage is a critical pathway to achieving carbon neutrality. However, a key challenge lies in how to balance multi-timescale adequacy and security to achieve the optimal portfolio of CFPP and energy storage resources. Therefore, this paper proposes a comprehensive assessment approach for the decision-making of VRE and energy storage integration, as well CFPP phase-out, taking power supply adequacy and frequency security into account. In addition, a comprehensive evaluation index system is constructed from technical, economic, and environmental perspectives to provide a reference for striving for the optimal generation and energy storage portfolio under the premise of ensuring the safe and stable operation during decarbonization. Considering frequent and large volatility of VRE generation leads to the risks of seasonal electric energy shortage and short-term power imbalance, even frequency insecurity, the assessment model decouples multi-timescale power and energy balance constraints into short-term power and long-term energy balances to achieve whole timescale power supply adequacy, fully leveraging the synergistic coordination of diverse resources across different timescales, meanwhile the rate of change of frequency (RoCoF) as an indicator of frequency security is embedded to decide CFPP phase-out. Case studies based on real-world datasets demonstrate that a strategic substitution of VRE and multi-temporal energy storage for CFPPs can significantly reduce the cost of low-carbon transition by 17% and promote a 52% reduction in carbon emissions compared to scenarios without CFPP substitution, while achieving a load shedding rate below 0.1% and a 98% VRE accommodation rate.