The role of coal plant retrofitting strategies in developing India's net-zero power system: A data-driven sub-national analysis

India set Nationally Determined Contribution (NDC) targets toward its net-zero carbon emission goal by 2070, which requires deep decarbonization of India's power generation sector. Yet, coal power generation contributes to more than 60% of the total, and policies still permit further coal fleet expansion and lifetime extensions. In this paper, we investigate the role of retrofitting India's coal plants for carbon capture and storage (CCS) and biomass co-firing in developing the net-zero power system. We model the power generation and transmission network expansions across 30 Indian regions in four representative technology scenarios under progressively tighter carbon emission caps, taking into account sub-national coal price variation and thermal efficiency of individual coal plants. Our analysis indicates that coal plant retrofitting with CCS could achieve gigawatt-scale deployment by 2035 if India reduces its annual carbon emissions from power generation to half of the 2021 level (i.e., 500 million tons of CO₂). Both renewable capacity expansion and coal plant retrofitting with CCS reduce the unabated coal plant capacity, electricity generation costs, and carbon abatement costs. While exploiting renewable energy potential remains the most cost-effective decarbonization strategy, it faces challenges of low coal plant utilization and the uneven geographical distribution of renewable generation investments.