Disused mines get a new lease of life and become part of the energy transition

Using disused mines as energy storage can be both cost-effective and environmentally friendly. Underground pumped storage power plants have great potential to become part of the energy transition by balancing the electricity grid and enabling more renewable electricity production.

Energy storage is a highly topical topic. So far, the focus has been on battery storage and hydrogen storage. Pumped storage power, which is already an established technology, has been somewhat neglected. But now it is being planned in a new guise and is expected to increase sharply as we move towards an energy system with increased elements of wind and solar power.

Pumped storage power is used in many applications around the world, but not so much in Sweden. There are currently three pumped storage power plants in operation, connected to existing power stations, with an output of 91 MW.

On a global scale, the installed capacity of pumped storage power (in 2021) was 165 GW, with China, Japan and the United States being the three largest countries with a share of 53%. It is estimated that the storage capacity corresponds to up to 9 TWh of electricity.

Pumped storage power technology is undergoing strong development. The International Hydropower Association (IHA) estimates that installed capacity will increase by almost 50% to 240 GW by 2030.

Energy storage technologies such as battery storage and pumped storage power plants will in all likelihood play an increasingly important role in the Swedish renewable energy system by primarily delivering frequency regulation services, such as fast frequency reserve (FFR) and frequency retention reserve (FCR) – something that Svenska kraftnät is in demand today.

Pumped storage power as a technology also contributes to swing mass and can support energy-intensive industries that want to optimize their electricity use or access backup power. There is also the opportunity to build business by exploiting price differences between different times of the day or seasons, although this is not the technology’s main competitive advantage.

Finn Jonung, a senior management consultant specialising in business and management issues at Rejlers’ Energy Division, says that the different energy storage technologies all have their specific niche with varying endurance and response time. He therefore believes that there is no competitive situation between them, but that they instead complement each other.

“Thanks to Rejlers’ broad expertise in energy storage, we can see the strengths of different technologies and always give the most optimal advice to the customer.

Rejlers’ offering for energy storage covers the entire process cycle, from feasibility studies, business cases, condition management, technology selection and optimisation, electricity connections, procurements, implementation and design of management plans.

“The energy industry is more important than ever, and it has never been so exciting to work with energy issues as it is now. We are facing a huge transition from fossil fuels to renewable energy, and it requires new solutions and innovations. I think it’s very interesting and meaningful to be part of that process, and to be able to contribute with my knowledge and experience to make a difference,” says Finn Jonung.

One of Rejlers’ clients in the power generation area is Svenska Mine Storage, which has developed a modular concept for underground pumped storage power. In this concept, disused mines are given new life, where water and gravity and reversible turbines form the basis for storing and releasing energy.

The company is developing projects in both Sweden and Finland, where the installed capacity in the first projects will be between 15-30 MW with a storage capacity of between 30-90 MWh. In addition, Mine Storage is developing projects together with Dairyland Power Cooperative in the US Mid-West region.

In the pumped storage technology that Mine Storage is developing, the technical equipment is placed underground. The only noticeable environmental impact is that the water level in the upper water reservoir, such as an existing mining dam, varies slightly.

Mine Storage has found a new way to use old mines as energy storage. It is a new area of application for established technologies, which can be of great importance for balancing the electricity grid and enabling more renewable electricity production. Finn Jonung concludes by stating:

“It is an exciting and challenging project, which requires a lot of technical and business expertise, creativity and collaboration. I am pleased that Rejlers is part of it, and that we can help Mine Storage realize its vision.

Rejlers has supported Mine Storage with project management and their plans to establish their energy storage solution in more countries. During the early phase of project development, Rejlers has also worked with technical solutions, hydraulic models, cost assessments and optimizations. In other customer assignments, Rejlers has been involved in several projects relating to energy storage, both with batteries, hydrogen and thermal storage.