There are various hydrogen energy storage configurations that offer different opportunities. The configuration analyzed below is bi-directional and utilizes fuel cells, referred to here as Hydrogen BDFC. This technology involves using a polymer electrolyte membrane (PEM) electrolyzer to generate hydrogen from water (releasing oxygen as a byproduct) with an electrical current before compressing and storing the hydrogen in underground salt caverns until it's needed. The hydrogen is later re-electrified using fuel cells to produce electricity.
There are alternative applications for the generated hydrogen as well, including injecting hydrogen into the gas grid (power-to-gas), using it for transportation (hydrogen-based vehicles), or in industry. There are also different methods to reconvert stored hydrogen into electricity other than fuel cells such as gas turbines or engines. Hydrogen energy storage is typically considered for long-duration applications.
Methodology for the cost and performance estimates for this technology can be downloaded here.