Wind-solar-storage trade-offs in a decarbonizing electricity system

Exploring cost-effective wind-solar-storage combinations to replace conventional fossil-fuelled power generation without compromising grid reliability becomes increasingly important in a steadily decarbonizing electricity system. For a renewable energy-rich state in Southern India (Karnataka), we systematically assess various wind-solar-storage energy mixes for alternate future scenarios, using Pareto frontiers. The simulated scenarios consider assumed growth in electricity demand, and different levels of base generation and supply-side flexibility from fossil fuels and hydropower. Our approach uses hourly load data, simulates generation based on hourly weather reanalysis data, and models the effects of battery charging and discharging on battery lifetimes. In the context of declining base generation and limited flexibility in the state electricity grid, the reliability of meeting demand is limited by the generation curtailment that is permitted. We show that adding battery storage capacity without concomitant expansion of renewable generation capacity is inefficient. Keeping the wind-solar installations within the officially assessed renewable potential, a fully decarbonized grid with limited flexibility can have approximately 63% reliability even after using adequate battery storage. Achieving 99% grid reliability would be expensive, requiring large wind-solar installations that exceed officially assessed potential, constrained by land allocation. The findings highlight the importance of a fresh examination of curtailment thresholds, available renewable potential, and possibilities of demand-side management based on consumers' willingness to modify hourly demand patterns.