Demand for battery energy storage systems (BESS) is increasing because they are reliable, support renewable energy and can help lower costs. In 2025, we put Wisconsin's first large-scale energy storage project — the Paris Solar-Battery Park in Kenosha County — into operation. The 110-megawatt (MW) storage facility is capable of powering more than 130,000 homes for four hours.
Think of a battery storage facility as a series of building blocks that come together to create the generation customers depend on:
- The first building block is the battery cell. Similar to a single AA battery, this lithium-ion battery holds the charge and releases energy when needed.
- The next block is the battery module — a group of battery cells packaged together as one unit.
- Modules are then stored on racks, which are tall cabinet-like structures.
- The racks are placed into containers, the outer shells of the storage system that also hold cooling and fire suppression equipment.
- Multiple racks make up the BESS site, providing reliable, cost-saving power to the energy grid.
Open container showing battery racks where modules and cells are stored.
Solar power after sunset
A BESS operates by taking excess energy from the grid when prices and demand are lower, storing the energy until demand is higher, then sending the energy back to the grid for customers to use. It is similar to a cellphone battery: you plug it in at night when you aren’t using it, then have a fully charged battery to draw from as you use the phone throughout the day.
BESS are typically built near solar generation facilities to charge the batteries when the sun is shining and grid demand is low. That surplus energy is stored in the BESS and deployed later in the day when the sun has set, customers return home from work, and electrical use goes up.
We continue to invest in BESS for their flexibility, cost savings and reliability, and currently have five sites under construction throughout Wisconsin:
- Darien Battery Park
- Koshkonong Battery Park
- High Noon Battery Park
- Saratoga Battery Park
- Dawn Harvest Battery Park
Together they total over 460 MW of energy storage, with anticipated in-service dates in 2027 and 2028. In addition, we are seeking approval from the Public Service Commission of Wisconsin for Dawn Break Battery Park, providing an additional 162 MW.
