Swiss company FlexBase has begun construction on the world's largest underground energy storage facility based on a redox flow battery. The facility is being built in Laufenburg, canton of Aargau, on a site known as the "Star of Laufenburg"—a historic hub of the European energy grid, reports swissinfo.

Construction of the Laufenburg Technology Center began in the spring of 2025. In addition to battery storage, it will include a water-cooled data center powered by artificial intelligence, office space, and laboratories.

To accommodate the battery's key components, a pit approximately 27 meters deep and longer than two football fields is being excavated. Once operational, the storage capacity will exceed 2,1 GWh and its output will exceed 1,2 GW—comparable to the Leibstadt nuclear power plant, located in the same canton.

The project is based on vanadium flow battery technology developed by Invinity Energy Systems. Unlike lithium-ion batteries, redox batteries store energy in large reservoirs of liquid electrolytes and are fire-resistant and do not degrade over many years of use.

According to calculations, the accumulated energy will be sufficient to supply 210 000 households with uninterrupted power for 24 hours. The facility's capacity will significantly exceed that of the current largest operating redox storage facility—China's Xinhua Ushi project, with a capacity of 700 MWh.

The facility is scheduled to be commissioned in 2029. The project is being implemented with private funding, without government participation, and is estimated to cost between 1 and 5 billion Swiss francs (1,2 USD and 6,2 billion USD). The project is expected to create approximately 300 jobs in the region.