Abandoned Mines Could Provide Energy Storage

It is recognized that large-scale energy storage is the key to the decarbonization of the electric power grid. Renewable energy sources like wind and solar only produce power when the wind is blowing or the sun is shining, so storing excess energy allows the grid to function at night or when the wind isn’t blowing. Although electrochemical storage using lithium-ion or flow batteries is getting all the attention at present, the reality is that a technology called pumped storage hydropower (PSH) accounts for more than 95 percent of grid energy storage in the United States.

 

The Quincy Mine in the Upper Peninsula of Michigan is an example of an abandoned mine that could be used for Pumped Underground Storage Hydro. Image used courtesy of Jason Mack, Michigan Tech

 

Two Elevations

In typical applications, PSH uses two water reservoirs at different elevations. Energy is stored when water is pumped from the lower reservoir to the upper one and power is generated as water moves down from the upper one to the lower one while passing through a turbine. The amount of energy that is stored depends upon the size of the reservoirs. The U.S. has about 22 gigawatts of electricity-generating capacity and 550 gigawatt-hours of energy storage within its pumped storage hydropower facilities spread over every region of the country.

One downside to PSH is the need for large tracts of land to build the reservoirs that hold the water. Building reservoirs can create environmental concerns and in addition, water is becoming scarce in some parts of the country.

 

PUSH

These potential limitations of PSH have led the Keweenaw Energy Transitions Lab (KETL) at Michigan Technological University (MTU) to explore the potential of adapting abandoned mines in Michigan’s Upper Peninsula (U.P.) into energy storage facilities. Michigan’s U.P. has a long history of copper and iron mining from the 1800s and is filled with abandoned mines. In fact, the KETL researchers found 968 suitable mines nationwide, mostly in the west and in the Upper Peninsula, which could be adapted as batteries for the electrical power grid using Pumped Underground Storage Hydro (PUSH).

This isn’t the first time that deep mines have been proposed for pumped storage hydropower. Finland has invested 26.3 million euros to develop one of Europe’s deepest mines for energy storage. In North America, the National Renewable Energy Laboratory (NREL) has said that the U.S. will need 120 gigawatts (GW) of storage to have an 80% renewable grid by 2050.

 

UP Case Study

The KETL study focused on Mather B, a decommissioned iron ore mine in Negaunee, Michigan. The team also extrapolated those results to consider the applicability of PUSH on a national scale. Combining the geospatial and economic analyses, KETL has determined that the U.S. has between 137 GW and 285 GW and 137 GW of power storage capacity nationwide for partially underground and fully underground PUSH facilities used for daily storage. The team also determined that PUSH could be used for long-term (seasonal) storage with a maximum cumulative power of 8.7 GW and energy capacities of 8,010 GWh based on four pumping/discharge cycles over a one-year period. The majority of PUSH opportunities exist in Western and Mid-Western states ( along with the U.P.) where deeper mining has been prevalent.

 

How it Works

PUSH is a closed-loop system whose upper reservoir is located either at or below ground level and the lower reservoir, along with the generating turbine, is built entirely underground. The KETL team looked at several possible scenarios by which the PUSH technology could be applied to existing mine sites. The following data was provided by MTU.

 

Scenario	High Volume Estimate (m3)	Low Volume Estimate (m3)	Maximum Head (m)
Scenario 1: Surface pond to Levels 11-12	13,536,062	4,583,673	1066
Scenario 2: Levels 2-4 to Levels 11-12	13,536,062	4,583,673	512
Scenario 3: Level 6-8 to Levels 11-12	13,536,062	4,583,673	274
Scenario 4: Surface to levels 7-12	33,800,000	18,551,208	792
Scenario 5: Shaft only	6,810	6,810	766

 

The economic feasibility of a PUSH system was also examined by KETL, and the team estimates the capital cost of building a Mather B PUSH facility would be $1.34 million per megawatt (MW) of storage capacity. This capital cost could be recovered a in variety of ways including participation in regional wholesale electricity markets. Complicating the cost estimates is the possibility of needing to deal with potentially contaminated mine water during PUSH operations. KETL conducted water quality testing on the Mather B site and found this particular mine location did not indicate major water quality concerns with potential outflows.

 

Local Benefits

Mining in the U.S. has largely been a boom-and-bust activity, particularly for communities that depend on mines for economic viability. Iron and copper mines were once the lifeblood of communities spread across the U.P. However, almost all have been closed for decades. This has thrown most of the region into economic despair. Despite this, there is a high level of community pride in how the metals mined from deep with the U.P. were used to build the country in the late 19th and throughout most of the 20th Century. The potential for PUSH could mean revitalization for post-mining communities through jobs and transformation “…into thriving economic development hubs — because of, and not despite, their heritage,” according to the KETL report.

 

Feature image used courtesy of Jason Mack, Michigan Tech