A study from the University of Minnesota-Duluth’s Natural Resources Research Institute (NRRI) finds the potential is there to re-purpose abandoned open pit iron ore mines in northeastern Minnesota’s Mesabi Iron Range to store energy from wind turbines and farms, according to a Midwest Energy News (MWEN) report. Doing so would not only enhance the competitiveness of wind power, it would make beneficial use of land that’s been severely degraded.
Wind energy has been growing fast in Minnesota, thanks to its geography, climate and impetus from the state’s Renewable Portfolio Standard (RPS), which requires that utilities and electric co-ops at least 25% of their electricity from qualifying renewable sources by 2025.
Being able to store wind energy at scale would be a major breakthrough. Wind power production is typically 25% of total rated capacity due to the intermittent nature of wind and the inability to store it when excess electricity is generated.
Wind power production typically picks up at night when wind energy is higher. Electricity demand is lower at night, however, and suppliers selling power into the grid at night typically receive significantly lower prices than they might if they could sell it during the day. Wholesale electricity prices in Texas, as well as other areas, actually dropped to zero due to high levels wind energy production recently.
A Relatively Simple, Clean & Highly Efficient Means of Storing Energy
Minnesota Power and Great River Energy, two Minnesota electric utilities that have signed large, long-term wind power purchasing agreements (PPAs), helped fund the NRRI study, which looked into the policy, topographical and environmental, as well as energy storage, aspects of hydroelectric pumped storage systems at abandoned open pit mines in the Mesabi Iron Range.
Hydroelectric pumped storage systems were first used in Italy and Switzerland in the 1890’s, Energy Journalism Fellow Dan Haugen writes for MWEN. Some 104 gigawatts (GW) of electricity capacity was stored in hydroelectric pumped storage systems worldwide in 2008, according to the US Energy Information Administration (EIA), with the US accounting for just over 22 GW, or around 21% of the total.
The system’s basic design requires a permanent reservoir of water at a lower elevation and a temporary holding pond at a higher elevation. In the case of storing energy from wind turbines and farms, the water would be pumped from the reservoir to the holding pond during the night and then released during the day, passing through a water turbine or turbines on their way back down to the reservoir during the day as required by electricity demand.
Hydroelectric pumped storage systems are highly efficient – 85% of the stored energy can typically be converted into usable power. They’re also relatively inexpensive to operate and maintain, and precise in their ability to deliver electrical power on demand.
They are costly to build, however. A 1,000-megawatt plant can cost around $2 billion to build. Using abandoned open pit mines that are already filled or partially filled with water would eliminate, or partly eliminate, one entire phase of construction, according to Haugen’s report. That would lower the up-front capital costs. A significant amount of capital would still need to be invested in equipment and drilling the system’s tunnels, one industry source told MWEN.
Cost and Other Considerations
Don Fosnacht, the study’s lead investigator and director of NRRI’s Center for Applied Research and Technology Development, told Haugen he thinks a 100-megawatt mining-pit system could be built be built for around $120 million, although that is just a rough estimate.
Environmental effects, along with the potential for abandoned iron ore mines to be reopened if iron ore prices continue to rise are also key considerations that the researchers and study sponsors need to evaluate in more detail before proceeding, however.
“It’s very difficult to manage [wind] without some kind of storage capability, and that’s where this type of project fits in,” Fosnacht was quoted as saying. On the Mesabi Iron Range, “the potential is certainly there, based on our study.”
“The Laurentian continental divide crosses the region, which slopes down from there several hundred feet to Lake Superior. Its topography is also pocked by just over 100 iron ore pits that were mined to varying degrees during the last century. Some are still used in taconite http://en.wikipedia.org/wiki/Taconite mining operations, but many are abandoned and have since filled with rain water,” Haugen writes.