Why long duration storage is best for Minnesota

Great River Energy (GRE) long-duration pilot project announcement generated many headlines recently. There were three things that the industry observers noted: 1) there is a new commercial grid-scale storage technology called aqueous air battery, 2) the pilot project is 150 hours duration and 3) GRE is retiring a baseload coal plant sooner than scheduled. Electric cooperatives are lightly regulated. Hence co-ops have some wiggle room to implement what their members want without seeking utility commission’s approval. Coop members are looking for more renewable energy; therefore, having viable long-duration storage makes sense. If this new technology pilot project is successful, the industry can expect large scale storage projects connected at the transmission node even in cold weather states like Minnesota.


GRE is a Transmission Owning (TO) member of the grid operator: Midcontinent Independent System Operator (MISO). GRE members like Connexus Energy are dependent on GRE for transmission. The latest announcement from GRE starts with retiring the 1,151 MW coal creek unit in 2022. GRE also wants to add an equal amount of wind by the end of 2023. GRE is in zone 1 of MISO’s resource adequacy construct. Unlike Investor Owned Utilities (IOUs) like Xcel Energy, Minnesota Power, and Otter Tail Power, GRE does not have to seek Minnesota Public Utilities Commission (PUC) approval. Coop members like Connexus drive GRE’s long-term power supply strategy.

An aqueous air battery system

Technology that GRE is piloting, the aqueous air battery system, is not entirely new to the storage experts immersed in mixing periodic table elements on both anode and cathode side. Lithium-Ion batteries are most-commonly used. Batteries discharge and provides energy when electrons flow from anode to cathode. An electrolyte basically “manages” electrons flow from anode to cathode or vice-versa. The Lithium-Air battery uses outside air as the cathode. A type of Lithium-Air batteries uses aqueous electrolyte. Hence the name Aqueous Air battery. Aqueous means something that contains water and aqueous air means, the air is the medium that conducts electricity.

Long duration storage is best for Minnesota winter

The size of the project is small – 1 MW, but the duration is long 150 hours (less than a week). For MISO capacity qualification, resources should show they are capable of discharging for four continuous hours. Pennsylvania New Jersey Maryland Interconnection (PJM) made a case for 8-10 hours duration storage recently in Federal Energy Regulatory Commission (FERC) Order 841 compliance filings. GRE expressed the need for long-duration storage during Minnesota Energy Storage study stakeholder meetings. Cold winters in Minnesota, the potential for ice-storms that “island” East and West Nebraska in Southwest Power Pool (SPP), and the bi-directional energy flows with Manitoba province in Canada – are all possible reasons for long-duration storage needs in this area.

MISO Market as backup

Minnesota Power’s Great Northern Transmission Line (GNTL) grabbed similar attention when first announced in 2012. At that time, MP said[1] that a long transmission line from Canada enables accessing the MISO market as a battery. MISO North region or MISO “classic” (before MISO South integration in December 2013) has more than 15 years of experience with market operations. As a result, MISO North utilities are gaining confidence in depending upon MISO energy market as a backup to their long term power supply strategy.

Solar needs Storage

In the MISO West region, which GRE is part of, there is 17,000 MW of renewable energy in the MISO generator interconnection queue as of May 2020. Approximately 40% of that queue in the west region is solar. Half of the solar in the western area is from Minnesota. As transmission connected solar penetration increases in the MISO region, MISO will start capacity credit calculation for solar. How much of the nameplate capacity gets counted towards meeting resource adequacy is capacity credit. This credit is another reason why long-duration storage makes sense for the MISO west region because storage increases the capacity value of solar.

Form Energy, a commercial spin-off from Argonne

George Crabtree[2], the Director of Joint Center for Energy Storage Research (JCESR) at Chicago’s Argonne National Laboratory, is proud of GRE’s announcement with Form Energy. Form Energy is one of the startups spun out of JCESR in its first five years of establishment. Sepion (focused more on the membrane in the electrolyte that separates anode and cathode) and Blue Current (focused on a nonflammable electrolyte) are the remaining two startups.

MISO Market registration process

Typically, we expect long-duration storage to be associated with pumped hydro storage. Department of Energy (DOE) Global Energy Storage database has two open-looped pumped storage projects with more than a thousand hours of duration in Portugal. Michigan’s utilities Detroit Edison (DTE) and Consumers Energy jointly own a 2,400 MW Ludington pumped storage facility. They raised concerns with MISO’s modeling of pumped storage charging/discharging in the market dispatch optimization algorithm during FERC Order 841 compliance stakeholder discussions. It is not clear if GRE has thought about the MISO market registration process for this 150-hour storage system.


  1. ^ MP said (energytransition.umn.edu)
  2. ^ George Crabtree (www.anl.gov)
  3. ^ Rao Konidena (www.renewableenergyworld.com)
  4. ^ View all posts by Rao Konidena (www.renewableenergyworld.com)

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