Gravity System Aids Storage in Unused Mine Shaft

An underground energy storage system utilizing heavy lift equipment and the force of gravity will soon be installed in a repurposed mine shaft at the 4,737-foot-deep Pyhäsalmi Mine in Finland. The project marks an innovative testbed for one of Europe’s oldest and deepest underground mines, containing copper, zinc, and pyrite. 

Scottish startup Gravitricity partnered with Callio Pyhäjärvi, an organization coordinating activities to reuse the mine for underground energy projects. The company will deploy its gravity energy storage system, GraviStore, to generate and store electricity by raising and lowering weights inside an unused 1,738-foot-deep auxiliary shaft along the 0.9-mile-deep mine. 

 

ABB installed this hoist at the Pyhäsalmi Mine in the early 2000s. Image used courtesy of ABB (Page 5)

 

The project marks the first full-scale demonstration of Gravitricity’s technology, which targets mines undergoing decommissioning activities. GraviStore gives mines like Pyhäsalmi a new life as they approach the end of their operations. The site’s closure plans are ongoing, with pyrite supply expected to continue until 2025. 

 

A 3D rendering of the Pyhäsalmi Mine in Finland. Image used courtesy of Callio

 

GraviStore will provide up to 2 MW of capacity and balancing services for the local electric grid, serving the rural Pyhäjärvi community. The system captures and stores energy in periods of low demand and releases it quickly when demand spikes. This is critical for sites partially powered by solar panels or wind turbines, which only provide intermittent renewable energy when the sun shines or the wind blows. The Pyhäsalmi Mine has an above-ground solar array.

 

GraviStore delivers and stores electricity through gravity-fed weights suspended in underground mine shafts. Image used courtesy of Gravitricity

 

What Is Underground Gravity Energy Storage?

Underground gravity energy storage is a relatively new market, with an estimated storage potential of 7 to 70 TWh worldwide, according to a 2023 study published in Energies. About 550 GWh of that total lies in Europe.

Generally, gravity energy storage systems discharge electricity by lowering large amounts of mass, such as sandbags or concrete blocks, into an area. GraviStore uses a suspended winch system to pull weights through an underground mine shaft. When excess electricity needs to be released, the winch system acts as a generator based on the speed of response required. The weight can be released quickly to meet peak demand or slowly for long-duration energy storage. 

Thousands of mines worldwide can be tapped for gravity energy storage. When co-located with renewable energy plants, the technology provides backup power and peak demand services to offset variable solar and wind generation. GraviStore offers critical grid balancing and frequency regulation functions for transmission and distribution network operators. 

 

GraviStore’s features. Image used courtesy of Gravitricity

 

GraviStore can support thousands of tons of mass for storing energy. In 2018, an Imperial College London assessment recognized it as a compelling alternative to conventional storage methods. Gravitricity’s system combines the advantages of pumped-storage hydropower and battery energy storage systems. Unlike those technologies, it offers increased versatility as it can be quickly dispatched or released slowly. GraviStore takes less than a second to get from zero to full power, whereas pumped hydro’s response time is several seconds to minutes. 

GraviStore boasts a 50-year lifespan (about 50,000 cycles) with minimal degradation and lower levelized costs than lithium-ion batteries. It has an 80% round-trip efficiency and a versatile energy-to-power ratio (15 minutes to 8 hours), with 97% availability. 

 

A 2018 assessment of Gravitricity’s technology compared to competing energy storage methods. Image used courtesy of Imperial College London - Storage Lab

 

GraviStore Will Use Hoist Technology from ABB

Gravitricity is expected to work with partners to finalize and install the system, including Switzerland-based equipment giant ABB and Huisman, a Dutch equipment producer specializing in deepwater and anchor-handling winches. 

ABB has developed more than 1,000 hoist systems, including one installed at the Pyhäsalmi Mine decades ago. The site began operating ABB’s 14-foot-wide hoist pulley powered by a 2.5 MW synchronous motor in 2001. The company recently upgraded the mine hoist with replacements for the old analog brake module and valve block. 

In December, ABB signed an agreement with Gravitricity to provide engineering and development teams specializing in mechanical, electrical, and control systems for mine hoists.