Sodium ion battery on the Wisconsin power grid
Peak Energy and RWE Americas are running a sodium ion battery, a rechargeable grid battery that stores electricity without lithium, cobalt, nickel or graphite, on the Wisconsin power grid for the first time. The pilot sits at an RWE Americas lab in eastern Wisconsin and connects to the regional grid run by the Midcontinent Independent System Operator, called MISO, which the American Clean Power Association says serves 45,000,000 consumers across 16 states and 1 Canadian province. Peak Energy calls the pilot the first sodium ion deployment on the MISO grid, not its first deployment anywhere, since an earlier version of the same GS1.1 battery system began running in Watkins, Colorado, in August 2025.
Passive cooling cuts the cost
The pilot system holds 3.1 megawatt hours, how much energy it can store, and can put out 775 kilowatts of power, a smaller unit than a megawatt, for 4 hours straight. Its cells use a chemistry called sodium iron pyrophosphate, which needs no active cooling, no fans, no pumps and no liquid, only resistive heating in cold weather. Peak Energy says that passive design cuts the power the system uses just to cool or heat itself by 95%, and says its systems can cut the total cost of a storage system by more than 25% against a conventional lithium ion system. Peak Energy states the Wisconsin deal cuts the lifetime cost of stored energy by an average of 70 dollars a kilowatt hour, a smaller unit of energy than a megawatt hour, about half the total price of a battery system today by its own account.
All 3 figures come from the Peak Energy specification page for the GS1.1 system, the same hardware being piloted in Wisconsin.
Show the numbers
| Guaranteed availability | 99 |
| Round trip efficiency | 96 |
| Auxiliary power reduction | 95 |
Energy storage is central to providing dispatchable, reliable energy on demand.
Landon Mossburg, chief executive officer of Peak Energy. Source 1.
A small pilot next to bigger deals
The Wisconsin pilot is a lab scale test, not a commercial rollout. Peak Energy has separately announced 2 supply agreements far larger than the Wisconsin system, a February 2026 agreement with Energy Vault for 1.5 gigawatt hours, a gigawatt equal to 1,000 megawatts, and a November 2025 agreement with Jupiter Power for up to 4.75 gigawatt hours. RWE Americas holds about 13 gigawatts of energy assets across the United States, Peak Energy states.
The Wisconsin row is a lab pilot. The other 2 rows are commercial supply agreements Peak Energy announced separately, far larger in scale.
Show the numbers
| RWE Americas Wisconsin pilot | 3.1 |
| Energy Vault agreement | 1,500 |
| Jupiter Power agreement, up to | 4,750 |
Why MISO wants more batteries
The pilot lands inside a specific regional pressure point. MISO summer 2025 capacity prices jumped more than 2,000%, the American Clean Power Association states, citing a study it commissioned from Aurora Energy Research. That study finds MISO needs a 500% rise in battery storage by 2035 to keep the grid reliable as demand grows, and projects that deploying 10 gigawatts of battery storage across the region, enough to power 8,000,000 homes at peak demand, could save consumers 25,000,000,000 dollars in energy costs over 2 decades, with 4,500,000,000 dollars of that saved in the next decade alone. The association also projects that buildout could cut evening price spikes by more than 60% between now and 2035.
Grid batteries deliver massive cost savings for families and businesses, while ensuring that the grid delivers power when it's needed most.
Noah Roberts, vice president of energy storage at the American Clean Power Association. Source 3.
The 25,000,000,000 dollar figure above comes from the account the American Clean Power Association gives of the study it commissioned, not from a Peak Energy press release describing the same study, because the commissioning association is the source in the best position to state what its own research found.