Electricity flows back to the grid in milliseconds
Beneath the Swiss canton of Aargau, workers are carving out a chamber the size of two football fields to house what may become the world's most consequential battery — a redox flow system capable of storing and releasing electricity at nuclear-plant scale. FlexBase Group's €5.5 billion wager in Laufenburg is less about a single facility than about a fundamental question Europe has not yet answered: how do you make renewable energy reliable? If the project delivers by 2029, it may mark the moment the continent's energy transition stopped being a promise and became an infrastructure.
- Europe is generating more renewable electricity than its grids can absorb, yet blackouts loom because solar and wind power vanish the moment conditions change.
- FlexBase Group is excavating a pit eight stories deep beneath Laufenburg, racing to complete the world's most powerful flow battery before the grid's balancing act becomes untenable.
- At 2.1 GWh of storage and 1.2 GW of instant discharge, the facility would match a nuclear plant's output — without the fuel, the waste, or the risk of fire.
- Redox flow technology, long sidelined by its appetite for space, is now being recast as the only chemistry durable and safe enough to operate at this underground scale.
- With commissioning targeted for 2029, Switzerland is positioning itself as Europe's energy storage benchmark — and every neighboring grid operator is paying close attention.
In Laufenburg, a town in the Swiss canton of Aargau, workers are digging a hole the size of two football fields and as deep as an eight-story building. Inside it, FlexBase Group intends to install the most powerful redox flow battery ever built — a system that can store 2.1 gigawatt-hours of energy and release 1.2 gigawatts in milliseconds, matching the output of Switzerland's Leibstadt nuclear plant. The price tag exceeds five and a half billion euros.
The project is a direct response to a contradiction at the heart of Europe's energy transition. Solar and wind installations are multiplying across the continent, but they produce power only when conditions cooperate. At the same time, demand is rising sharply — driven by electric vehicles, heat pumps, and data centers. Without large-scale storage, surplus renewable energy is wasted and shortfalls risk blackouts.
Redox flow batteries address this mismatch by storing energy in liquid electrolytes rather than solid compounds. When charged, electricity alters the chemical state of the fluid; when discharged, the reaction reverses and power returns to the grid. The technology degrades far more slowly than lithium alternatives and carries a safer profile — FlexBase's aqueous electrolyte is non-flammable, non-explosive, and recyclable. The trade-off is space, which is precisely why a purpose-built underground facility in Laufenburg makes sense.
If construction stays on schedule, the battery will begin operating in 2029. The engineering challenges are substantial but understood, and excavation is already underway. Should the project succeed, Switzerland would demonstrate that intermittent renewables can be made reliably dispatchable — not through ideology, but through infrastructure that finally matches the scale of the problem.
In the canton of Aargau, in a place called Laufenburg, Switzerland is digging a hole the size of two football fields and as deep as an eight-story building. When finished, it will hold the most powerful redox flow battery ever built—a machine designed to store and release electricity at a scale that rivals a nuclear power plant. The company behind it, FlexBase Group, is betting more than five and a half billion euros that this underground chamber will help solve one of Europe's most urgent problems: what to do with all the renewable energy the continent is racing to generate.
The numbers are striking. The battery will store 2.1 gigawatt-hours of energy and release 1.2 gigawatts in milliseconds—the same output as the Leibstadt nuclear facility. Those figures matter because Europe is caught between two contradictory needs. Solar panels and wind turbines are proliferating across the continent, but they only work when the sun shines or the wind blows. Meanwhile, demand for electricity is climbing: electric vehicles are multiplying, heat pumps are replacing gas furnaces, and data centers are consuming more power than ever. The grid needs a way to store surplus energy and release it on demand, or blackouts will follow.
Redox flow batteries are not new technology. They trace their roots to the nineteenth century and were refined by NASA. Unlike the lithium batteries in phones and electric cars, which store energy in solid chemical compounds, redox flow systems pump liquid electrolytes through tanks. When the battery charges, electricity transforms the liquid's chemical state. When it discharges, the process reverses and electricity flows back to the grid. The advantage is durability: these batteries degrade far more slowly than lithium alternatives and can operate for years without significant capacity loss. The disadvantage is obvious—they need enormous space. A redox flow battery cannot fit in a car or a basement. It needs a dedicated facility, which is why Laufenburg, with its geology and infrastructure, became the chosen site.
FlexBase's design uses an aqueous electrolyte with high water content. The company claims it is non-flammable, non-explosive, and recyclable—a safety profile that matters when you are storing gigawatt-hours of energy underground. The logic is straightforward: capture electricity when renewable sources overproduce, on days when the sun blazes or the wind howls. Release it when demand spikes or generation falters. The system acts as a buffer, smoothing the mismatch between when power is made and when it is needed.
If the schedule holds, the battery should begin operating in 2029. That timeline is ambitious but not impossible. The excavation itself is already underway, and the engineering challenges, while substantial, are well understood. What matters is what comes after. If Laufenburg succeeds, Switzerland becomes a model for the rest of Europe—proof that large-scale energy storage is not a theoretical problem but a solvable one. Other nations will watch, learn, and build their own facilities. The grid becomes more stable. Renewable energy stops being intermittent and becomes reliable. The transition away from fossil fuels accelerates not because of ideology but because the engineering finally works.
Notable Quotes
The system is designed to be non-flammable, non-explosive, and recyclable— FlexBase Group
The Hearth Conversation Another angle on the story
Why does a battery need to be this big? Can't we just use more lithium batteries?
Lithium batteries degrade quickly under heavy use and can only cycle so many times before they fail. A redox flow battery can cycle thousands of times with minimal degradation. For a grid that needs to store and release energy day after day for decades, that durability matters enormously.
So the tradeoff is size for longevity?
Exactly. Lithium is compact but temporary. Redox flow is massive but permanent. You can't put it in a car, but you can put it under a mountain.
Why Switzerland specifically? Why not somewhere else in Europe?
Geology, infrastructure, and political stability. Switzerland has the engineering expertise, the grid capacity to absorb that much power, and the regulatory environment to permit something this ambitious. It's not just about digging a hole—it's about having a country that can actually build it.
What happens if it works? Does Europe suddenly have enough storage?
No. One battery, even this one, is not enough for an entire continent. But it proves the concept works at scale. Once you prove it, you build ten more, then fifty more. It becomes the template.
And if it fails?
Then Europe has a five-billion-euro hole in the ground and a harder time convincing investors that large-scale storage is viable. The entire transition slows down.