A group of researchers at Michigan Technological University (MTU) say a fully renewable energy grid could be achieved if the US converted mines to hydro-powered batteries. Such mines could pave the way for the “most ambitious” renewable energy targets in much of the country.
The need for more energy storage has become “absolutely urgent” as renewable energy sources have become more widespread, says Associate Professor Timothy Scarlett, an archaeologist with the MTU research team. Wind and solar energy production outpaces our ability to use or store it, creating bottlenecks of pent-up energy that can lead to wasted energy and blackouts.
Scarlett explains that converting the mines to act as batteries would stabilize the wind- and solar-powered grid, absorbing excess power and balancing outages when there is either too much or too little power.
What are the opportunities and barriers to converting decommissioned mines into Pumped Ground Water (PUSH) facilities? This question was investigated at MTU’s Keweenaw Energy Transitions Lab (KETL), whose main goal is to explore, explore and develop pathways for transforming old environmental and economic liabilities into productive clean energy assets for the benefit of sustainable and prosperous communities.
The PUSH study focuses on a decommissioned iron ore mine in Negaunee, Michigan, but it doesn’t stop there. Based on the data collected, the team expands the results to consider the applicability of PUSH on a national scale.
Funded by a grant from the Arthur P. Sloan Foundation, the KETL team is investigating the potential of adapting an abandoned mine in Michigan’s Upper Peninsula (UP) for energy storage. Michigan’s UP has copper and iron mining regions full of abandoned mines that present environmental and economic challenges. Using a government database, the researchers found 968 suitable mines, mostly in the west and Upper Peninsula. Several of these mines are very large, giving them enormous energy potential as batteries for the electrical grid.
The communities that live with these historic mines have complex relationships with them, but appreciate their symbolic role as heritage sites, places of memory and sources of tourism. Given these contexts, the KETL study was about much more than just renewable energy applications.
Instead, the researchers asked, “Can PUSH devices be designed to enhance heritage values while transforming the energy system? The report concludes that PUSH can help economically distressed areas transform into thriving centers of economic development—because of, not in spite of, their legacy.
“A pumped water tank is the best solution, and an underground pumped water tank is the most elegant of the best solutions,” explains Scarlett. (Note: Scarlett reached out CleanTechnica following up on an article we published in 2019 about the early stages of their project.)
The National Renewable Energy Laboratory said the US needs 120 gigawatts of storage to have an 80% renewable grid by 2050; the country had about 23 gigawatts in 2020.
The technology behind hydro-powered batteries
PUSH is a type of closed-loop pumped hydro (PSH) technology, where the upper reservoir is located either on or below the ground surface, while the lower reservoir and turbomachinery are built entirely underground.
This closed-loop PSH application is capable of providing essential grid services while mitigating and repairing environmental damage caused by past mining activities and offering sustainable economic development opportunities for post-mining communities. These PUSH attributes can ease the complexity of the licensing and permitting process and improve the economic feasibility of PUSH devices.
A case study in Negaunee, Michigan, showed the mine could provide extremely long-term storage and offer continuous power to 30,000 people for 3.5 months – at a profit – once built.
The team collected data from a variety of sources: community outreach; historical records from local archives, including documents such as surface and underground mine maps and other company records; and oral histories of mine operations and community life. Each has proven helpful in analyzing mine dimensions, structural integrity, soil and water contamination, property rights and designs.
PUSH devices can be developed using advanced technological systems – materials and machinery – used by conventional PSHs. In what they call a conservative estimate, the researchers determined that the U.S. has between 137 and 285 gigawatts of storage capacity within nearly 1,000 mines likely suitable for PUSH.
Based on their analyses, the team made several high-volume and low-volume reservoir and elevation estimates that translated into 5 fully and partially underground PUSH designs.
Data provided by MTU
Using these designs, the team calculated nameplate and energy storage capacities for several scenarios across 3 models.
- The first model calculated the maximum installed capacity rating with a 7-hour discharge time for the partially and fully underground PUSH facilities using high and low volume estimates of available upper and lower reservoirs. The main goal of this model is to demonstrate the potential of a system requiring high performance. The team does not believe that this model contains realistic case study siting options, as both current market conditions and transmission and distribution infrastructure are highly unlikely to accommodate facilities with these rated capacities.
- The second model simulates daily energy storage scenarios that are based on the site characteristics listed above. This model represents the most realistic design options that can be developed on site.
- The third model extends the second model to explore the potential of PUSH as a solution for long-term energy storage. The third model scenarios have the largest storage capacities for fully and partially underground PUSH facilities. Although similar to the first model, this model appears to be more practical as it is not constrained by the limitations of the first model and is not likely to require the construction of additional shafts.
Dealing with potentially contaminated mine water during the dewatering and operational phases is likely to be a challenge, the researchers note.
Final thoughts
Through their study of “Strengthening the electricity grid and community resilience through the conversion of decommissioned mines to underground pumping facilities”, KETL scientists found that options for a renewable energy transition are available and in the public interest through problem-solving approaches such as energy storage, mine reclamation and rural economic development. Together, these elements can help achieve greater energy equity.
Analyzing the technical, economic, legal, regulatory, water quality, social and community engagement dimensions, the PUSH team saw their work as an opportunity to bring sustainable economic resources to communities abandoned and struggling due to mining. with reclamation and revitalization.
Projects of this kind are already underway in Europe. Finland invested 26.3 million euros last year to convert one of the continent’s deepest mines into energy storage.
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