The concept which is based on pumped hydroelectric energy, closed water circulation and existing mine infrastructure in the depth of the Pyhäsalmi Mine, has “no impact” on the environment. Pyhäjärvi’s “water battery” is based on mature technology used in more than 96 % of world’s energy storages. In addition to its long operational lifetime, generous size of the energy storage (7 h), high volume of the water reservoir (162 000 m3) and great effectiveness (77 %), it has minimal operating costs with limited maintenance and replacement investments.

Initial situation
Finland’s coal use currently falls in what is referred as the entirety within the scope of the emissions trading scheme of the EU. A copper and zinc mine has been operating in Pyhäjärvi, located in the Oulu Region in Finland, since the 1960s. The mine is Europe’s deepest base metal mine and will stop underground operations at the end of 2019

Solution
Re-using the deepest base metal mine in Europe enhances Finnish renewable energy and climate strategies. According to a feasibility study report made by Pöyry Energy GmbH this unique project can now be fully realized. Energy Storage in Mine project financed by the Northern Ostrobothnia Centre for Economic Development, Transport and the Environment (ELY Centers) shows that the underground energy storage plant can be put into practice after the mine closure in late 2019.

Innovation
The existing mine infrastructure is well suited for an energy storage plant. Mine depth enables having head of 1400m which is the world record in the field. The location is good, as it is close to the Finnish transmission grid. There is available backfill quarry on surface that can be used as an upper reservoir. In the mine, there are good and well-known rock conditions.