The increasing frequency and severity of extreme weather events highlight the urgency of addressing climate change. Developing countries like India are particularly vulnerable. India has committed to ambitious renewable energy targets (450 GW by 2030 and net-zero emissions by 2070), but aligning this growth with social and economic development priorities is crucial. Historically, India's power sector has relied heavily on coal, resulting in high greenhouse gas emissions, air pollution, and water stress. However, declining renewable energy costs, particularly solar PV, present a compelling economic case for a rapid transition. This study investigates the feasibility and cost-effectiveness of a complete shift to renewable energy sources in the Indian power sector by 2050, considering the unique challenges and opportunities presented by India's diverse geography and energy demands. The research focuses on analyzing a cost-optimal transition pathway at the state level, integrating various generation options, storage technologies, and interstate transmission to meet hourly power demand. This approach will address two key questions: (1) Is a 100% renewable energy-based power system technically feasible and the least-cost option by 2050? (2) What are the required generation capacities, storage, and flexibility needs at the state and national levels during the transition?

Existing long-term transition studies on India's emission reduction pathways often focus solely on a national level, lack high temporal and spatial resolution, include limited storage and flexibility options, fail to show a clear transition pathway, and consider limited renewable penetration. While some studies explore 100% renewable energy scenarios, they often lack detail in one or more of the mentioned aspects. This study aims to overcome these limitations by providing a state-level analysis with high temporal and spatial resolution, incorporating various storage and flexibility options, detailing a clear transition pathway, and considering high shares of renewable energy penetration.

The study utilizes the LUT Energy System Transition Model, a tool used to assess techno-economic energy transition pathways at various scales. India is divided into 22 states/regions, grouped into four major interconnected regional grids. The model linearly optimizes a cost-optimal capacity mix of generation, storage, transmission, and flexibility technologies to meet hourly power demand for each state over an entire year. Two key constraints are implemented: no new fossil fuel or nuclear power plants after 2015 (except for those already under construction or commissioned by 2019), and a maximum annual growth of 4% in renewable energy capacity share after 2020. The model incorporates distributed self-generation and consumption by residential, commercial, and industrial prosumers (using a separate sub-model for cost optimization of rooftop solar PV and batteries), thus reducing the demand of the centralized power system. The optimization considers capital expenditures (CAPEX), weighted average cost of capital (WACC), operational expenditures (OPEX), ramping costs, fuel costs, and GHG emission costs for all technologies. Detailed financial and technical assumptions for each technology are provided in the Supplementary Information. Hourly profiles for solar PV, wind, and hydropower are based on high-resolution spatial data. Renewable energy potentials are determined based on land use limitations and specific capacity densities. The model is designed to analyze the technical feasibility of a 100% renewable energy system and calculate its costs, comparing them to a scenario with continuing fossil fuel use. The analysis covers capacity expansion, electricity generation, storage deployment, electricity import/export, seasonal power system analysis, and the financial implications of the transition.

The cost-optimal transition pathway shows significant growth in solar PV and wind capacities across all states. During the first decade, larger states like Uttar Pradesh and Maharashtra experience substantial solar PV capacity additions, while states with good wind resources see significant wind energy capacity increases. After 2030, solar PV dominates, reaching almost 3000 GW by 2050, supported by large-scale battery storage. Wind capacity growth slows, reaching around 410 GW. Hydropower sees growth in regions with favorable resources. The share of coal declines dramatically, with many plants at risk of becoming stranded assets due to reduced profitability and the cost competitiveness of renewables. Gas turbines and multi-fuel reciprocating internal combustion engines (ICE) are installed to provide flexibility, especially for evening peak demands. Transmission capacity expansion significantly improves resource variability management and reduces local storage needs. The share of coal in electricity generation decreases by over 60% in 2030, with solar PV accounting for 73% of generation in 2050, wind 19%, and other renewables and flexible technologies fulfilling the remainder. Storage capacity grows substantially, with batteries providing most of the short-term storage output and gas storage for seasonal balancing. Interstate electricity trade increases significantly, with some states becoming net exporters and others net importers, enhancing overall system efficiency and cost-effectiveness. The levelised cost of electricity (LCOE) decreases from around 71 €/MWh in 2020 to 38 €/MWh in 2050, even without considering carbon emission costs. GHG emissions from the power sector decline dramatically, approaching zero by 2040. Seasonal analysis reveals operational differences between summer (high solar, battery use) and monsoon (high wind, hydropower) seasons.

The findings demonstrate the technical and economic feasibility of a rapid, cost-optimal transition to a 100% renewable energy-based power system in India by 2050. The transition is driven by the declining cost of solar PV and batteries. The model effectively highlights the complementary nature of solar and wind energy resources, particularly the ability of wind energy to supplement solar generation during monsoon seasons. Interstate electricity trade is crucial in balancing regional resource variability. The significant reduction in LCOE compared to a coal-dominated system shows that rapid decarbonization is not only environmentally beneficial but also economically advantageous. The dramatic decrease in GHG emissions aligns with India's climate goals and contributes to global climate mitigation efforts. This study effectively addresses limitations of previous research by providing a detailed, state-level analysis with high temporal and spatial resolution, incorporating various storage and flexibility technologies, and demonstrating a clear transition pathway.

This study shows that a rapid transition to a 100% renewable energy-based power system in India by 2050 is both technically feasible and economically advantageous. Solar PV, coupled with batteries and supported by wind energy, hydropower, and flexible technologies, forms the backbone of this system, significantly reducing LCOE and GHG emissions while improving energy security and reliability. The results highlight the importance of policy support, investment in transmission infrastructure, and flexible generation capacity to facilitate a smooth and effective transition. Future research could explore the integration of other sectors (heat, transport, industry) and further refine the analysis of uncertainties associated with technology cost developments, resource availability, and societal factors.

The study presents a best-policy scenario, assuming perfect foresight of resource availability and demand. Uncertainties regarding future technology cost developments, policy stability, and societal acceptance are not fully captured. The model focuses on the power sector; other sectors could impact electricity demand and require further integration. The study assumes that the necessary infrastructure upgrades are made in parallel to the changes described here and no technical bottlenecks occur during the transition. These limitations should be considered when interpreting the findings.