What are the best options for long-duration energy storage? A techno-economic comparison of technologies including hybrid energy storage systems

As the energy sector strives for decarbonization, long-duration storage solutions are emerging as enablers of high-renewable power systems. This study investigates hybrid energy storage, combining Li-ion batteries, pumped hydro storage, and underground hydrogen storage, as an effective approach to enhance the reliability and economics of high-renewable power systems, supporting deep decarbonization goals. To facilitate techno-economic evaluation, we developed an open-access Python module capable of simulating renewable energy systems across different renewable penetration levels, ensuring flexibility and reproducibility for future research. Results indicate that optimal renewable penetration significantly increases from a baseline of 31% to 39% with compressed air, 49% with hydrogen, 53% with pumped hydro, and 56% with hybrid storage. Compared to a baseline battery-only scenario, the hybrid approach reduces the required renewable capacity by 61% and lowers the levelized cost of storage by 81%. Additionally, relative to standalone storage technologies, hybrid storage reduces capacities needed for electrolyzers by 46.3%, fuel cells by 79.7%, batteries by 96.4%, powerhouses by 39.7%, underground caverns by 50.6%, and upper reservoirs by 69%. The results demonstrate that hybrid energy storage significantly improves both technical feasibility and economic viability, establishing it as a superior long-duration energy storage solution for facilitating renewable energy integration.