Inside Switzerland’s massive underground flow battery that could power 210,000 homes for a day without lithium-ion cells

Switzerland is developing what could become one of the world's largest underground energy storage facilities, aimed at storing renewable electricity on a large scale and supplying power when demand places pressure on the grid.

The project, being developed by Flexbase with support from Invinity Energy Systems, is expected to be completed by 2029. Early reports indicate the facility will have a storage capacity of about 2.1 GWh and a power output of up to 1.2 GW, enough to provide electricity to approximately 210,000 homes for a full day.

Vanadium flow technology at the core

Despite being described as a battery, the facility differs significantly from conventional battery systems used in consumer electronics, vehicles or typical grid storage applications.


The project will use vanadium redox flow technology, which stores energy in liquid electrolytes contained in large tanks. When electricity is required, the liquids are circulated through the system to generate power.

According to engineers, flow batteries experience less performance degradation over long operating cycles than lithium-ion batteries. The technology is also non-flammable, making it suitable for large underground installations where thermal safety is a key consideration.

Capacity designed to support grid stability

The storage system will be capable of holding 2.1 GWh of electricity and delivering power at a rate of 1.2 GW. At full capacity, this would be sufficient to supply around 210,000 homes for 24 hours.

Beyond storage volume, the facility is intended to help manage fluctuations in electricity demand. Power consumption typically rises during morning and evening hours and falls overnight, requiring grids to maintain a constant balance between supply and demand.

The system is designed to respond rapidly by releasing stored energy during periods of increased demand, helping stabilise electricity networks.

Strategic location near major European power hub

The project is being built near the Star of Laufenburg substation, a major electricity junction connecting Switzerland, Germany and France.

Its location places the facility at a key point where cross-border electricity flows are continually changing, allowing it to support regional grid operations.

Alternative to lithium-ion for long-duration storage

While lithium-ion batteries remain dominant in consumer devices and electric vehicles, flow batteries are increasingly being considered for long-duration energy storage applications.

Unlike lithium-ion systems, flow batteries separate energy storage capacity from power generation capability. This allows storage capacity to be expanded without redesigning the entire system.

Engineers highlight longer operational life, improved safety at large scale and modular expansion as key advantages of the technology.

Linked to planned AI data centre complex

A notable aspect of the project is its connection to a planned 500 MW AI data centre complex being developed alongside the storage facility.

AI infrastructure requires large amounts of stable electricity for training models and operating computing systems. By combining large-scale energy storage with a data centre, the project aims to smooth electricity demand and reduce dependence on fossil fuel backup power during peak usage periods.

Addressing renewable energy timing challenges

The project is designed to tackle one of the main challenges associated with renewable energy: matching electricity supply with demand.

Solar generation peaks during daylight hours, while wind output depends on weather conditions. Electricity demand, however, follows consumption patterns that do not always align with renewable generation.

By storing surplus renewable electricity when supply is high and releasing it when demand increases, the facility is expected to reduce pressure on power grids, lower reliance on fossil fuel backup plants, improve cross-border energy sharing in Europe and enhance the reliability of renewable energy systems.