Minnesota permit moves Spearmint Energy’s 600 MWh Midwater battery closer to construction

Spearmint Energy has secured Minnesota Public Utilities Commission approval for the Midwater Energy Storage Project, a proposed 150 MW / 600 MWh standalone battery system in Freeborn County. The four-hour facility would occupy between 10 and 20 acres beside the Glenworth Substation in Shell Rock Township and connect through a new 2,668-foot, 161 kV transmission line. The decision gives Spearmint its second permitted battery project in Minnesota and strengthens its development position inside the Midcontinent Independent System Operator market. Midwater could store electricity during lower-demand periods and return it when system demand or grid stress is higher, adding flexible capacity to southern Minnesota. However, the site permit does not confirm completion of MISO interconnection work, project financing, equipment procurement, an offtake structure or a construction notice to proceed.

What has the Minnesota Public Utilities Commission approved for the Midwater battery project?

The Minnesota Public Utilities Commission’s decision covers the site permit for Midwater’s proposed battery energy storage facility. The permit represents a major land-use and environmental approval for a project of this scale, but it should not be interpreted as a final investment decision or a declaration that construction is ready to begin.

Midwater BESS, LLC, a subsidiary of Spearmint Renewable Development Company, submitted the project through Minnesota’s state permitting process. The associated regulatory proceedings are identified as dockets ESS-24-294 and TL-24-295.

The application proposed an alternating-current battery facility capable of delivering up to 150 MW and storing approximately 600 MWh. Dividing the energy capacity by the power rating indicates a four-hour discharge duration at the project’s maximum rated output.

The project was also filed with an application for a route permit covering a 2,668-foot high-voltage transmission line. The line would operate at 161 kV and connect Midwater with the existing Glenworth Substation.

Spearmint’s announcement specifically highlights approval of the site permit. It does not separately state whether the route permit for the transmission facilities was issued on the same terms. The final Commission order will therefore be important for confirming the complete approval package, applicable construction conditions and any continuing obligations attached to the transmission connection.

Midwater went through environmental assessment, public-hearing and administrative review processes before reaching the Commission. The environmental assessment was issued in February 2026, followed by in-person and virtual hearings in March. The public comment period closed later that month, and an administrative law judge issued findings and recommendations in May.

That history makes the approval more substantial than an early-stage project announcement. Spearmint has secured control of a viable site, advanced environmental review and moved through a public regulatory process. Yet the permit remains one component of the broader development sequence required to turn Midwater into an operating infrastructure asset.

Why does Midwater’s location beside the Glenworth Substation matter for grid integration?

Midwater is planned for privately owned land off Minnesota Highway 65 in Shell Rock Township. The site’s proximity to the Glenworth Substation is strategically important because grid-scale batteries need a practical and economically viable point of interconnection.

A short transmission connection can reduce the amount of new linear infrastructure required compared with a project located several miles from a suitable substation. It may also limit land requirements, routing complexity, construction interfaces and certain permitting risks.

The proposed 2,668-foot connection is still a significant piece of high-voltage infrastructure. It requires engineering, protection systems, metering, communications equipment and coordination with the transmission owner and MISO. A short line does not eliminate the possibility of network upgrades elsewhere on the system.

The critical question is not simply whether the battery can be physically connected to the Glenworth Substation. It is whether MISO’s studies determine that the project can charge and discharge at its proposed capacity without creating unacceptable reliability effects or requiring prohibitively expensive upgrades.

Interconnection studies can identify costs for substation modifications, transmission reinforcements, protection equipment and other network work. The timing and allocation of those costs can materially affect project economics.

Midwater’s dedicated project materials identify an interconnection agreement as a targeted milestone for autumn 2026. They also state that construction and mobilisation depend on MISO’s ability to meet its posted deadlines. That language indicates the interconnection process remains an important schedule dependency rather than a completed formality.

The site itself is expected to occupy approximately 10 to 20 acres. Project materials say existing vegetation to the north and east should screen the facility from occupied dwellings. Such screening could reduce visual impacts, although noise, lighting, drainage, traffic, emergency access and construction activity remain relevant matters during detailed design and permit compliance.

How could a 150 MW / 600 MWh battery support southern Minnesota and MISO reliability?

A 150 MW / 600 MWh battery can discharge at its full 150 MW rating for approximately four hours, subject to operating constraints, state of charge, degradation and auxiliary power consumption. This duration makes Midwater potentially useful during concentrated periods of high demand or reduced supply.

The Minnesota Public Utilities Commission has described the project’s proposed capacity as sufficient to serve the equivalent of approximately 100,000 households for up to four hours. That comparison illustrates scale, but it does not mean the project would operate as an isolated four-hour backup system for a fixed group of homes.

Midwater would participate in an interconnected regional electricity system. Its actual dispatch would depend on market prices, transmission conditions, operating instructions, contractual commitments and the services for which it qualifies.

Battery storage does not create primary energy. It consumes electricity while charging, retains part of that energy and releases the remainder later. Round-trip losses mean less electricity is returned than was originally used to charge the system.

Its value comes from timing, speed and controllability. A battery can charge when power is relatively abundant or less expensive and discharge when it is more valuable to the grid. It can also respond rapidly to changes in system conditions, subject to its market registration and technical configuration.

Potential applications include energy shifting, peak-demand support, operating reserves, frequency response and other ancillary services. The project could also help manage variability associated with wind and solar generation by moving some electricity from periods of high renewable output into tighter operating periods.

Four-hour storage is particularly relevant because many system peaks and steep ramps occur over several hours rather than entire days. However, a four-hour battery cannot independently solve a prolonged supply shortage. Its reliability contribution depends on entering a stressed period with sufficient charge and being dispatched at the right time.

The project’s commercial performance will likewise depend on disciplined optimisation. Excessive cycling can accelerate degradation, while overly conservative operation can leave revenue opportunities unused. Spearmint will need to balance immediate market value against battery life, warranty limits and long-term availability.

Where does Midwater fit within Spearmint Energy’s national battery storage portfolio?

Midwater is Spearmint Energy’s second project to advance through Minnesota’s state permitting system. Its first was the 150 MW / 600 MWh Snowshoe Energy Storage Project in Olmsted County, which became Minnesota’s first permitted standalone battery project of its type.

The two projects give Spearmint a potential 300 MW / 1,200 MWh battery platform in Minnesota. Both are four-hour systems, but they have separate sites, interconnection points, permits and execution requirements.

The Minnesota developments represent geographic diversification for a company whose operating portfolio is currently concentrated in the Electric Reliability Council of Texas market. Spearmint reports that it operates 350 MW / 700 MWh of battery capacity in ERCOT.

That portfolio includes the 150 MW / 300 MWh Revolution project and the 100 MW / 200 MWh Tierra Seca and Seven Flags facilities. Tierra Seca and Seven Flags reached commercial operation in 2026 after Spearmint secured more than $250 million in construction and tax-related financing for the projects.

Spearmint is also constructing Red Egret, a 300 MW / 600 MWh battery project in Texas City. The company closed approximately $450 million of financing for Red Egret, including a $225 million construction facility, $96 million of preferred equity and approximately $126 million connected with an investment tax credit transfer commitment.

That financing demonstrates Spearmint’s ability to assemble complex capital packages for advanced battery projects. It does not establish that similar funding has been secured for Midwater.

Moving from ERCOT into MISO also introduces a different regulatory and commercial environment. Market rules, capacity accreditation, transmission arrangements, congestion patterns and revenue opportunities differ across regional transmission organisations.

Spearmint’s operational experience in Texas could still provide transferable capabilities in battery optimisation, procurement, construction management and risk control. Midwater will test whether the company can apply those capabilities successfully within MISO while navigating a longer state permitting and interconnection process.

Which milestones still stand between Midwater’s permit and the start of construction?

Interconnection is the most visible remaining dependency. Midwater must obtain the necessary rights and agreements to connect with the transmission system, establish its upgrade responsibilities and coordinate the completion of any required network work.

The project also needs a fully committed capital structure. Spearmint has not disclosed Midwater’s expected construction cost, debt package, equity commitment, tax-credit strategy or financing timetable.

Utility-scale battery developments commonly rely on combinations of sponsor equity, construction debt, term financing, tax-credit transfers and contracted or merchant revenue assumptions. Lenders and investors usually require confidence in interconnection costs, equipment warranties, construction contracts, revenue forecasts and operating risks before releasing capital.

Midwater’s commercial structure has not been announced. It is therefore unclear whether the project will pursue a long-term tolling or capacity arrangement, utility procurement, a partially contracted strategy or greater exposure to wholesale market revenues.

The answer will affect financing terms and risk allocation. A long-term contract can improve revenue predictability, but its pricing and operational restrictions may limit upside. Merchant exposure can capture stronger market conditions, but it increases sensitivity to price spreads, competition and changing market rules.

Spearmint has also not named a battery supplier, engineering and construction contractor or long-term service provider for Midwater. These agreements will determine equipment availability, performance guarantees, completion protections and the allocation of construction risk.

Public schedules for Midwater have evolved. Minnesota’s project portal previously indicated construction could begin in the first quarter of 2027, with commercial operation by the end of that year. The dedicated Midwater website now identifies construction during winter 2027 to 2028 and commercial operation in spring 2028.

The more recent schedule also makes clear that the dates are estimates and depend on MISO interconnection timing. Spring 2028 is consequently the more cautious operational target until Spearmint confirms financing, contracting, interconnection and a formal notice to proceed.

How could safety, land-use and environmental conditions affect Midwater’s execution?

Battery storage projects concentrate substantial amounts of electrochemical energy within a relatively small area. Their designs must therefore address thermal events, fire detection, isolation, emergency response, ventilation, drainage and access for first responders.

Earlier project materials indicated that Midwater expects to use lithium iron phosphate battery technology. This chemistry is generally considered more thermally stable than some nickel-based lithium-ion chemistries, but it does not eliminate fire or thermal-runaway risks.

The final equipment selection will determine the applicable system architecture and safety controls. Container spacing, fire barriers, monitoring systems, water access and emergency shutdown procedures will all influence the project’s risk profile.

Minnesota’s review of Spearmint’s Snowshoe project demonstrated that emergency preparedness can become a material permitting issue. Conditions associated with that project included coordination with local authorities and first responders, analysis of water access, specialised emergency equipment and training obligations.

Midwater’s final permit conditions will need to be assessed independently. The Commission may impose project-specific obligations related to emergency response, noise, setbacks, visual screening, stormwater management, vegetation, construction hours and decommissioning.

The project’s relatively limited land footprint is an advantage compared with many generation assets. It does not require a large fuel supply, broad solar array or extensive wind-turbine spacing. Nevertheless, temporary construction disturbance could be considerably larger than the permanent operating footprint.

Long-term decommissioning is another important issue. Batteries, power-conversion systems and electrical equipment will eventually need to be removed, recycled, repurposed or replaced. A credible decommissioning plan should identify financial responsibility and prevent those future costs from being transferred to landowners or local authorities.

Community acceptance will depend on more than compliance with technical standards. Spearmint will need to maintain communication with Freeborn County, Shell Rock Township, emergency services, neighbouring landowners and other local stakeholders through construction and operation.

What will determine whether Midwater becomes an economically durable MISO storage asset?

A site permit gives Midwater development value, but the project’s long-term economics will be determined by its interconnection position, construction cost, financing structure and ability to earn sustainable revenue.

The first major variable is network-upgrade exposure. Unexpected transmission costs can weaken returns or delay financing, even when the battery site and gen-tie route appear straightforward.

Equipment pricing and performance are also critical. Battery costs have generally declined over time, but project economics remain exposed to tariffs, logistics, domestic-content rules, supplier bankability and changes in federal tax policy.

Spearmint must choose a system capable of meeting MISO operating requirements while preserving sufficient flexibility for multiple market services. The project’s four-hour duration could support both energy and capacity applications, but the value attributed to those services can change as MISO adjusts its accreditation and market rules.

Competition is another factor. MISO’s interconnection pipeline contains a large volume of proposed storage and hybrid projects. Only a portion will reach construction, but those that do could reduce price volatility and compress the market spreads on which merchant batteries depend.

Battery degradation creates an additional economic trade-off. Each cycle consumes part of the asset’s useful life. Midwater may require augmentation or equipment replacement to preserve its 600 MWh rating over the operating period.

A successful project will therefore require more than buying power at low prices and selling it at high prices. It will need sophisticated bidding, accurate forecasting, maintenance planning, warranty management and control of charging costs.

Midwater’s location, four-hour configuration and regulatory progress give it credible development foundations. Spearmint’s financing and operating record in ERCOT also strengthens the case that the company can move sophisticated battery assets from development into operation.

The remaining uncertainty is whether the company can convert those advantages into an executable MISO project. Confirmation of interconnection, route rights, financing, major contractors and a commercial strategy would provide the clearest evidence that Midwater has moved from permitted development into committed infrastructure.

What are the key takeaways from Spearmint Energy’s Midwater battery permit?

• The Minnesota Public Utilities Commission has approved a site permit for Spearmint Energy’s Midwater Energy Storage Project.
• Midwater is designed as a 150 MW / 600 MWh standalone battery facility with approximately four hours of storage duration.
• The project would occupy between 10 and 20 acres in Shell Rock Township, Freeborn County.
• Midwater plans to connect with the Glenworth Substation through a 2,668-foot, 161 kV transmission line.
• The project represents Spearmint’s second permitted battery development in Minnesota after the Snowshoe Energy Storage Project.
• Spearmint currently operates 350 MW / 700 MWh of battery capacity in ERCOT, giving it relevant construction and operational experience.
• The company has not announced Midwater’s construction cost, financing package, equipment supplier, contractor or revenue structure.
• The interconnection agreement and any associated network-upgrade requirements remain central execution risks.
• Current project materials target construction during winter 2027 to 2028 and commercial operation in spring 2028, subject to MISO’s timetable.
• The site permit is a significant development milestone, but it does not constitute a final investment decision or construction notice to proceed.