The deepest metal mine in Europe, unused since 2022, is set to host a giant underground gravity battery.

Pyhäsalmi Mine, located 450 kilometers north of Helsinki in Finland, runs deep into the Earth - 1,444 meters, or around 0.9 miles, to be precise. With its copper and zinc deposits depleted, Pyhäsalmi has a lot of vertical space sitting unused that's perfect for capturing the energy of heavy weights being dropped down a shaft, which is precisely what Scottish energy storage tech firm Gravitricity plans to use it for.

First reported by Glaswegian news outlet The Herald, Gravitricity's intent for the Finnish mine isn't, sadly, a mile-high gravity battery, but a smaller one in a 530-meter (1,738 ft) auxiliary shaft. Once complete, the battery will apparently be able to achieve two megawatt-hours of storage capacity.

"This project will demonstrate at full scale how our technology can offer reliable long-life energy storage that can capture and store energy during periods of low demand and release it rapidly when required," Gravitricity executive chairman Martin Wright told The Herald.

A gravity battery is just what it sounds like: Excess energy generated by power plants is used to move a material upward - in Gravitricity's case it's heavy weights in a mine shaft raised by winches - and when there's an energy shortage the load is dropped and the energy is harvested.

Gravity batteries aren't a new idea, and Gravitricity's weight-cable-winch design isn't the only one out there. Liquid pumped between reservoirs at different elevations, loaded-up train cars pushed up and down hills capturing energy with regenerative brakes, and large buoyant cylinders pulled underwater and returned to the surface have all been proposed or tested over the years.

The idea with all the various gravity battery designs is to supplement energy systems in times of shortage - a need becoming doubly important as the world attempts to transition away from fossil fuels toward renewables like solar and wind, also known as variable renewable energy sources.

That's not to say gravity batteries don't have their detractors. Scaling remains difficult, and the amount of energy generated by a gravity battery is minuscule compared to traditional batteries, though it is far cheaper per megawatt-hour.

We were unable to reach Gravitricity for comment, but the firm told The Herald that it had signed a deal with Callio Pyhäjärvi, a special development firm set up to develop reuse projects for the Pyhäsalmi Mine, for the prototype. The project's timetable isn't available (we've asked), nor is it clear whether Gravitricity plans to build additional batteries in the mine if the prototype proves successful.

Nonetheless, "this full-scale project will provide a pathway to other commercial projects and allow our solution to be embedded into mine decommissioning activities, offering a potential future for mines approaching the end of their original service life," Wright said.

While many gravity battery systems have been designed to operate on the surface, putting them underground could have a massive effect on energy shortfalls. According to research published in early 2023, the number of abandoned underground mines is growing globally as fossil fuel usage decreases, pollution concerns grow and resources dry up.

It's challenging to estimate the total number of abandoned mines globally, the paper's authors admit, but they say there are more than half a million in the US alone, many of which could be repurposed with gravity batteries.

If the world's abandoned mines - primarily concentrated in the US, China, India, and Russia - were repurposed into gravity batteries, as much as 70 terawatt-hours could be captured, the researchers concluded. ®

https://www.theregister.com//2024/02/08/europe_deepest_mine_battery/