Thermal energy storage cavern twice the size of Madison Square Garden could heat Finland's fourth-most-populous city of Vantaa all year.

Engineering advancements have recently made strides in sustainability by imitating nature as opposed to conquering it. In the case of storage, the global energy transition demands more powerful and efficient batteries as well as earth-friendly processes to get the technology where it needs to be, and one city in Finland is building the world's largest battery of its kind from the earth itself.

Energy storage at its most basic is potential force, motion, and power on command, derived from any number of resources to work machines that give us light, heat, and tools that will all one day run cleanly and sustainably.

That potential can be amassed and extracted in a variety of ways, from compressed air and water reservoirs or pressure from steam, utilizing the downward force of gravity, the heat and photons from the sun, and natural forces pushing turbines – all generating the power we need to work, travel and build.

A number of large-scale energy storage solutions are needed to deal with the intermittent nature of some renewable energy sources, such as wind and solar, if cities and industries are to fully wean themselves from fossil fuels.

Batteries, even those designed for grid-scale storage, aren't yet efficient enough to meet all the longer-term, mass energy storage needs of cities. Though recycling and alternate sources are regularly being discovered, lithium-based batteries, by far the most popular in production, rely on nonrenewable minerals that need to be mined.

To offset this, companies are developing more earth-friendly, large-scale methods of efficient energy storage, such as pumped hydro energy storage and industrial-scale sand or crushed rock thermal storage batteries fabricated around natural processes.

A cave of wonders

Vantaan Energia has announced that it will construct a 90-gigawatt-hour seasonal thermal energy storage facility in a massive cavern – twice the size of Madison Square Garden – capable of heating Finland's fourth-most-populous city of Vantaa for a year.

"The world is undergoing a huge energy transition," Vantaan Energia CEO Jukka Toivonen told New Atlas. "Wind and solar power have become vital technologies in the transition from fossil fuels to clean energy. The biggest challenge of the energy transition so far has been the inability to store these intermittent forms of energy for later use. Unfortunately, small-scale storage solutions, such as batteries or accumulators, are not sufficient; large, industrial-scale storage solutions are needed."

The facility will be built in Vantaa's bedrock, excavating a total of three caverns about 20 meters wide, 300 meters long and 40 meters high. The bottom of the caverns will rest 100 meters below ground level with a total volume of over a million cubic meters, including processing facilities.

Specially designed areas will be filled with hot, pressurized water, reaching temperatures up to 140 degrees Celsius (280 degrees Fahrenheit) without boiling or evaporating.

This is a substantial first step towards an eventual hybrid heating system to be built in Vantaa, providing the city options for efficient, AI-based solutions to the city's power needs throughout the year, and securing affordable and stable prices for customers, all while eliminating emissions.

The facility is expected to come online in 2028.