Switzerland breaks ground on world's most powerful battery

A construction crew in northern Switzerland is excavating a pit the size of two football pitches and 27 metres deep that will house the world's most powerful battery when it opens in 2029 — a $1bn-plus redox flow installation capable of supplying 210,000 households with power for an entire day and injecting or absorbing electricity faster than the eye can blink.

The project is being built by Swiss energy company FlexBase, and represents both a record-breaking scale-up of a Victorian-era technology and a bet that long-duration grid storage will become essential infrastructure as renewables penetration deepens and AI data centre demand surges.

"We will be able to inject or absorb up to 1.2 gigawatt-hours of electricity in a few milliseconds," FlexBase co-founder Marcel Aumer told Swiss public broadcaster RTS, describing a responsiveness that makes the installation useful not just for storing energy but for providing the near-instantaneous grid balancing services that system operators require as coal and gas plants retire.

The project is part of the battery revolution that is sweeping the world that can complete the green energy transformation by supply grid-level storage capacity that allows cheap power generated during the day to be stored and released during peak demand times in the early evening. The FlexBase flow installation battery follows on from a massive sand battery that has been developed in Finland that can heat a whole town for a week, as innovations unfold.

The technology

Redox flow batteries store energy in liquid electrolytes held in large tanks — in FlexBase's case, vanadium-based solutions — which are pumped through a cell with a membrane separating positive and negative sides. Charging and discharging involves ions transferring through that membrane, changing oxidation states. The chemistry is inert, making the battery non-flammable. It is also almost completely recyclable and, crucially for grid operators, has a practically unlimited cycle life — unlike lithium-ion batteries, which degrade with repeated charging.

The technology was first theorised in 1879 and modernised through NASA research between the 1950s and 1970s. Lithium-ion subsequently dominated the market for consumer and short-duration storage applications, but redox flow has been gaining ground at grid scale where long-duration storage — measured in hours rather than minutes — and longevity matter more than energy density or weight.

FlexBase says the component costs for redox flow systems — tanks, membranes, cell stacks and pumps — have fallen significantly as the industry has matured, improving the economics of the technology at scale.

The scale

At 2.1 gigawatt-hours of capacity, the FlexBase installation will be comfortably the largest of its kind in the world. China's Xinhua Ushi project in Inner Mongolia, currently the largest operational redox flow battery, has a capacity of 700 megawatt-hours — the Swiss installation will be three times larger. Japan and Germany have also invested significantly in the technology, but neither has a project approaching this scale.

The site sits near the German border in northern Switzerland, in the same region as the Leibstadt nuclear power plant — whose total electrical output of approximately 1.2 gigawatt-hours is matched by the speed at which FlexBase's battery can inject or absorb energy. The battery will be fed by excess generation from wind turbines in the area, storing it during periods of low demand and releasing it during peaks.

When the 215,000-square-foot technology complex opens in 2029, the battery will share the site with a data centre, laboratories and offices. AI data centres in the region — whose power demand is both large and predictably spiky — are identified as a primary commercial customer for the installation's flexibility services alongside its grid stabilisation role.

The FlexBase project arrives as the European energy storage market accelerates. The Iran war's disruption to global gas supply has reinforced the strategic case for energy storage that can bridge the gap between intermittent renewables and steady demand — exactly the niche that long-duration flow batteries are designed to fill.