FLASC, based in Delft in the Netherlands, stores energy by using a liquid piston to compress air, keeping the air in submerged steel storage and using the surrounding water as a heat sink so compression stays close to constant temperature, then reversing the process to return electricity to the grid. The company says its system reaches 70% round-trip efficiency and can store energy for 4 to 100 hours, designed for 30 years of life, according to FLASC. Its EIC Accelerator project, FLASC HPES, receives an EU contribution of €2,499,991 towards a total cost of €3,571,416 and runs from January 2025 to December 2026, according to CORDIS.
The project is to build a grid-connected pilot plant in Rotterdam to validate key performance data and complete qualification "ahead of market entry", according to FLASC. The project report says a site was secured and permitted, suppliers were making key components for delivery in the first quarter of 2026, control software was developed in simulation, and the full testing campaign was planned for 2026, "on schedule and on budget", according to CORDIS. In July 2026 FLASC posted a timelapse of the 125 kW onshore pilot's construction. No test results have been published.
Company file
- Legal entity
- FLASC B.V., Delft
- Technology
- Hydro-pneumatic energy storage with a liquid piston
- Pilot
- 125 kW grid-connected onshore pilot, Rotterdam
- Partner
- Subsea 7
- Other projects
- OESTER, Offshore for Sure, MUSICA, PowerBundle
- Target market
- Offshore wind farms, onshore sites with water bodies
- EIC funding
- Blended finance, €2.5M grant
Where FLASC Stands Now
FLASC's website now presents the technology for both offshore and onshore sites with a suitable water body and grid access, and says it is hiring. It quotes Subsea 7's vice president of strategy and technology calling it "a competitive and more sustainable alternative to Li-ion battery farms". It cites a 2030 levelised cost of storage of €89 per megawatt-hour, benchmarked against a US Department of Energy study of other technologies. Its funding and accounts have not been published.
"Overall, the project remains on schedule and on budget, and the technical foundations are now in place for the full testing and measurement campaign planned for 2026."
FLASC, EIC project reportThe Technology: Air, Water and Steel
FLASC pre-charges its storage pneumatically rather than relying on water depth, and uses the sea, or another body of water, to absorb heat so compression is nearly isothermal. The EIC project summary ties it to the EU's REPowerEU goal of 60 gigawatts of offshore wind by 2030, which will need storage to smooth output.
What the EIC Award Promised, and What the Record Shows
The project runs until December 2026, so it is too early to judge it. It promised a grid-connected pilot and final qualification. By July 2026 the pilot was being built. Whether it will be tested and qualified before the project ends, and whether it meets the efficiency claims, is not yet known.
- Site and permitsDeliveredProject report.
- Pilot constructionUnder wayJuly 2026.
- Performance validationPendingNo results yet.
- First commercial projectUnverifiedNone announced.
The Money
The EU covers 70% of the project. The award was blended finance, but no EIC Fund investment or private round has been announced, and FLASC's accounts were not accessible in free sources.
What Cannot Be Checked
Questions for the EIC
Whether the EIC Fund invested, who else funds FLASC, when the Rotterdam pilot will start operating and what efficiency it achieves are not public.
Why Europe Should Care
FLASC argues that offshore wind needs storage to cope with intermittency, grid congestion and price swings. It offers a battery-free option built from steel and water. The Rotterdam pilot will be the first real test of whether its numbers hold.
What the award promised
A grid-connected pilot and final qualification before market entry.
What the record shows
A permitted site and a pilot under construction in mid-2026.
The Verdict
Building, not yet proven
FLASC is on the path the EIC funded. The pilot's results will decide whether it is ready for the sea.
FLASC and the EIC have not been asked for comment for this article. It is based entirely on public records and published statements, linked throughout.
