In this work, we perform a techno-economic analysis on using hydrogen underground storage (HUS) for grid electricity storage, comparing two control strategies, fixed setpoint (SP) control and dynamic control, via dynamic simulations and optimization. Both strategies demonstrate similar arbitrage profit margins, generating approximately $40.74 million and$41.74 million annually, based on 2022 CAISO grid data. A primary challenge identified for HUS in electricity storage is the significant capital investment required for electrolyzers and combined cycle power plants (CCPP), coupled with a lower capital utilization rate due to lower round-trip efficiency. To enhance the economic attractiveness of the HUS system, the study proposes a novel solution: leveraging natural gas (NG) for power generation when the CCPP is not in operation. This strategy significantly boosts the CCPP's operational time and increases the net present value to an appealing $21.94 million per year. The research concludes with a positive outlook on HUS's potential as a sustainable and economically viable grid electricity storage solution.