Something unusual is happening deep beneath Switzerland, and it is not getting much attention outside energy circles yet. Engineers are building what could become one of the world’s largest underground energy storage systems, designed to store renewable electricity on a massive scale and release it when the grid is under pressure.Early reports suggest the system could hold around 2.1 GWh of energy and deliver up to 1.2 GW of power, enough to supply roughly 210,000 homes for an entire day. It is being developed by Flexbase with support from Invinity Energy Systems, and is expected to be completed by 2029.
Inside Switzerland’s world’s largest underground battery: What makes this unique
At first glance, calling it a “battery” is slightly misleading. This is not the kind of system you would find in a phone, a car, or even a typical grid storage plant.Instead, it uses vanadium redox flow technology, which stores energy in liquid electrolytes kept in large tanks. When electricity is needed, the liquids are circulated through the system to generate power. That one design choice changes everything.Unlike lithium-ion systems, which slowly degrade over time, flow batteries behave more steadily across long cycles. Engineers say they can run for decades with far less performance loss. Another detail matters more than people realise. The system is non-flammable, which makes it safer for large underground deployments where thermal risks are a serious concern.
How it can power 210,000 homes without breaking a sweat
The headline number sounds almost abstract until you break it down. At full capacity, the system stores 2.1 GWh of electricity and can release energy at a rate of 1.2 GW. In real terms, that is enough electricity to power around 210,000 homes for 24 hours.But here is what makes it more interesting. This is not just about total energy. It is about timing. Electricity demand is messy. It spikes in the morning, surges again in the evening, and drops overnight. Power grids have to balance this second by second, or risk instability.This system is designed to react almost instantly, releasing stored energy when demand suddenly rises. Think of it less like a backup generator and more like a shock absorber for the entire grid.It is also strategically placed near the Star of Laufenburg substation, one of Europe’s key electricity junctions linking Switzerland, Germany and France. That location is not random. It sits right where cross-border energy flows are constantly shifting.
Why engineers are moving beyond lithium-ion
Lithium-ion batteries dominate everything from phones to electric vehicles, but they are not perfect for long-duration grid storage. Flow batteries are gaining attention because they solve a different problem entirely.Instead of packing energy and power into one compact unit, they separate the two. That means energy capacity can be expanded without redesigning the system itself.Engineers point to three reasons this matters:
- They last longer with slower degradation
- They are safer at large scale
- They can be expanded in a modular way
Unexpected link with AI data centres
One detail that makes this project stand out is its connection to a 500 MW AI data centre complex being developed alongside it. AI systems are extremely energy-intensive, and demand is rising faster than most grids can comfortably handle. Training models and running large-scale computing infrastructure requires constant, stable electricity.By pairing a massive storage system with a data centre, the idea is to smooth out energy demand and reduce reliance on fossil fuel backup power during peak usage.
Why this project matters more than it looks
The real problem with renewable energy is not generation anymore, It is timing. Solar power peaks in the middle of the day. Wind power depends on weather conditions. But electricity demand follows human behaviour, not nature.This underground system is designed to fix exactly that. It stores excess renewable energy when supply is high and releases it when demand rises.If scaled successfully, systems like this could:
- Reduce strain on national grids
- Cut dependence on fossil fuel backup plants
- Improve cross-border energy sharing in Europe
- Make renewable energy far more reliable in practice
There is a quiet but important shift happening here. Energy is no longer just about producing more. It is about controlling when and how it is used.
