Spain’s Fundación Ciudad de la Energía (CIUDEN) has completed operational testing of a sodium-sulfur (NaS) battery storage facility designed to integrate with green hydrogen production.
The system, operating at 305°C and with a minimum nominal capacity of 5.8 MWh, is part of CIUDEN’s broader effort to generate industrial-scale data on hydrogen and energy storage technologies under the EU-funded Recovery, Transformation and Resilience Plan (PRTR).
The NaS battery system—implemented by Spanish contractor CYMI of the COBRA IS group and supplied by Japanese manufacturer NGK through BASF—was validated through commissioning, performance, and hot and cold start-up tests. Results confirmed compliance with tender specifications, including a maximum charge/discharge rating of 1,000/750 kW. With a project budget of €4.84 million, the installation marks one of the few large-scale NaS deployments in Europe, a region where lithium-ion technologies dominate storage investment.
CIUDEN’s testbed in Cubillos del Sil links the NaS batteries with a 2.1 MWp solar PV plant and two electrolyzer types: a polymer electrolyte membrane (PEM) system and a solid oxide electrolysis cell (SOEC). By pairing these assets, the project aims to assess how high-temperature NaS storage interacts with variable renewable generation and hydrogen electrolysis under different usage scenarios. Key metrics under review include efficiency, system compatibility, cost reduction potential, and security of supply.
This dual-technology electrolyzer setup is particularly significant for the hydrogen sector. PEM systems are already commercializing, while SOECs promise higher efficiency when paired with waste heat sources, but remain at an earlier stage of deployment. Data generated by CIUDEN could therefore help clarify the trade-offs between the two approaches in real-world hybrid systems.
Revisiting Sodium-Sulfur in Europe’s Storage Mix
While lithium-ion has become the de facto choice for grid-scale storage, NaS batteries retain advantages worth revisiting. With energy densities around 150–240 Wh/kg and proven service lives exceeding 15 years in commercial projects in Japan and the Middle East, NaS offers long-duration storage potential at competitive raw material costs. The need to maintain operating temperatures of 300–340°C, however, has historically limited wider adoption due to energy losses and safety concerns.
CIUDEN’s project seeks to test whether coupling NaS with renewables and hydrogen production mitigates these drawbacks. By leveraging existing heat integration with SOEC electrolyzers, efficiency penalties could be reduced, improving system economics. If successful, such hybridization could provide a template for diversifying Europe’s storage portfolio beyond lithium-ion, particularly as demand for raw materials like cobalt and nickel tightens supply chains.
Stay updated on the latest in energy! Follow us on LinkedIn, Facebook, and X for real-time news and insights. Don’t miss out on exclusive interviews and webinars—subscribe to our YouTube channel today! Join our community and be part of the conversation shaping the future of energy.
