Achieving net-zero emissions in highly electrified power systems requires addressing seasonal mismatches between demand and renewable energy supply. This study investigates the role of hydrogen as a seasonal storage technology in enabling a fully decarbonized electricity system in Victoria, Australia. We develop a mixed-integer linear programming model with hourly resolution to jointly optimize generation, storage, and conversion technologies for the projected 2050 demand. The results show that underground hydrogen storage (UHS) is the most cost-effective seasonal storage technology, supplying up to 46% of electricity demand during prolonged winter renewable droughts. Even under scenarios with substantially reduced hydrogen demand, UHS remains economically optimal, highlighting its value as a seasonal storage asset rather than solely as hydrogen supply infrastructure. In contrast, scenarios excluding hydrogen storage increase total system cost by up to 63% and require unrealistically large deployment of pumped hydro energy storage. These results suggest that net-zero system planning in Victoria should prioritize hydrogen infrastructure in conjunction with renewable generation. Despite substantial storage capacity, the optimal system still exhibits 23% renewable curtailment, primarily driven by summer solar PV overgeneration, indicating that renewable overbuild can remain a cost-effective adequacy strategy. The analysis adopts a deterministic, system-level framework and does not explicitly represent spatial network constraints, transmission expansion, non-linear operational dynamics, future efficiency improvements for wind and solar technologies, or stochastic supply and demand uncertainty, which are identified as priorities for future research. • Winter peak demand growth drives rising seasonal storage needs in Victoria. • Batteries, hydrogen, demand response, and hydro secure supply in variable renewable energy droughts. • Excluding hydrogen storage shifts seasonal needs to pumped hydro, raising costs by 63%. • Low hydrogen demand scenarios still show the value of underground hydrogen storage for electrical purposes. • Overbuild leads to 23% curtailment of variable renewable generation.
Bastarrica et al. (Sun,) studied this question.