The Minnesota Public Utilities Commission issued a site permit on July 16 for Spearmint Energy’s Midwater Energy Storage Project, a 150 MW / 600 MWh standalone battery site in Shell Rock Township, Freeborn County. It is the developer’s second Minnesota approval in less than a year, following the identically sized Snowshoe project in Olmsted County that cleared the same commission in 2025 as the state’s first standalone storage permit.
The specifics. Midwater sits on 10 to 20 acres of private land next to the Glenworth Substation off Minnesota Highway 65. The MPUC filing pegs installed capital cost at approximately $457 million, with roughly $246 million in operating costs over the project life. Spearmint plans a modular enclosure layout built around Tesla Megapack 2XL lithium iron phosphate modules and a 2,668 foot 161 kV interconnection tie to the substation. Construction is targeted for Q1 2027, with commercial operation by year-end 2027.
Why it matters for MISO. Standalone storage build in MISO has trailed ERCOT and CAISO by a wide margin, largely because state permitting frameworks were later to arrive and interconnection studies inside MISO’s cluster process have been slow. Two 600 MWh approvals from the same developer in the same state, at the same MPUC docket standard, is a data point that Minnesota’s process is now routine rather than novel. The precedent Snowshoe set in 2025 for the review timeline shows up here as replicability, which is the input queue economics respond to.
Supply chain read. LFP Megapack 2XL selection continues the pattern seen in every Minnesota, Massachusetts, and California utility filing this month: developers are locking in Tesla LFP for four hour duration blocks near substations, financing on the assumption that domestic content and Section 45X credits stay legible after OBBBA guidance. If FEOC ratios tighten further, the material assistance question sits inside the Megapack bill of materials, not on the plot plan.
Watch list. Spearmint has now approved 300 MWh in Minnesota, with 400 MWh under construction in ERCOT via the Kyuden International investment announced in January. The next signal is whether the Midwater interconnection agreement lands inside MISO’s revised cluster window before Q1 2027 construction start, or whether the schedule slips into the next study cycle. That is where the state permitting speed either translates into steel in the ground or stalls at the queue.