Large-scale energy storage systems help intermittent resources, like solar and wind, provide service regardless of weather conditions. These systems allow for surplus energy to be stored and redistributed to the grid when needed. This process decreases stress on the grid, lowers energy costs, and increases renewable energy reliability.¹

Energy Storage Technologies and Regulation

Common energy storage technologies include thermal systems, pumped hydro facilities, batteries, and compressed air systems. The most common of these is battery storage.

Battery energy storage systems (BESS) are a form of large-scale energy storage that uses various types of batteries. Lithium-ion batteries are currently the most common type of battery used in BESS. BESS can be paired with electricity generating equipment, but there are also facilities dedicated solely to battery storage.²

While batteries as a concept go back to ancient times, large-scale batteries have only recently emerged as a mainstay of the electric grid.³ The traditional electric grid was designed to take power from large power stations – nuclear, coal, or hydroelectric, for example – and move it through the transmission system to end-use customers, matching demand with supply as closely as possible. As a result, utility regulation developed rules governing the construction of utility infrastructure that considered generation and transmission.

Given that provision of electricity is a statewide concern, policymakers developed statewide schemes under Wis. Stat. section 196.491 (2022) for reviewing large generation and transmission projects and awarding a Certificate of Public Convenience and Necessity (CPCN) to qualifying projects.

CPCN, BESS, and Wisconsin Statutes

Unfortunately, Wis. Stat. section 196.491(e) – the CPCN statute – does not address large-scale energy storage by name – likely because it was written before this technology became deployable. Facilities explicitly eligible for a CPCN under the law are either large electric generating facilities or high-voltage transmission lines.

While the issue is yet to be directly decided, a standalone BESS may not qualify for a CPCN under the current law. A project made up solely of a BESS may not meet the requirements to be considered a high-voltage transmission line.

Wis. Stat. section 196.491(f) defines a high-voltage transmission line as

a conductor of electric energy exceeding one mile in length designed for operation at a nominal voltage of 100 kilovolts … together with associated facilities.

Battery-only facilities could be considered a “a conductor of electric energy,” but they are unlikely to meet the statutory requirement of exceeding one continuous mile in length. A BESS also may not be “electric generating equipment and [it’s] associated facilities designed for nominal operation at a capacity of 100 megawatts or more.”⁴

Wis. Stat. section 196.52(2) specifies that electric generating equipment and their associated facilities work together to form “a complete facility for the generation of electricity.”⁵ Generating equipment is defined by the U.S. Energy Information Administration (EIA) as a device that converts a form of energy into electricity.⁶

Additionally, a battery’s nominal capacity refers to the amount of energy it can deliver under specific conditions, measured in kilowatt hours (kWh) or megawatt hours (MWh).⁷ This is different from a traditional electric generator’s capacity, which is measured by the maximum power output the generator can produce, measured in kilowatts or megawatts.⁸

Because standalone BESS do not generate any more electricity than they store, and often lose electricity in storage,⁹ and are measured in different nominal operation capacities, they may not qualify under the CPCN law.

Further Considerations​

Legislators behind Wis. Stat. section 196.491 may have intended for the CPCN statute to cover battery-only facilities. The statute’s legislative notes state that the law’s major purpose was to involve state agencies, such as the Public Service Commission and the Department of Natural Resources, in the construction process of large electric generating facilities. The involvement of state agencies was intended to help recognize and balance the needs of the utilities, the consumers, and the environment.¹⁰

The CPCN statute was also intended to increase the reliability of Wisconsin’s electric generation and streamline the construction process.¹¹

Certification for standalone BESS facilities may align with lawmaker’s intent. Although battery-only facilities don’t generate electricity, they do have a similar impact on utilities, the consumers, and the environment as transmission and generation, and can increase reliability.

Status Uncertain

The relationship between standalone storage facilities and Wisconsin's state-specific large energy project certification scheme is currently uncertain. As standalone storage increasingly offer solutions to various challenges in the energy system, practitioners, regulators, and courts will need to assess how storage integrates within existing regulatory frameworks.

This article was originally published on the State Bar of Wisconsin’s Public Utilities Blog. Visit the State Bar sections or the Public Utilities Section webpages to learn more about the benefits of section membership.

Endnotes

¹ For more information, see “What is BESS and how does it work,” Enel X; and “Clean energy storage facts,” American Clean Power.

²See “Types of Energy Storage,” New York State Energy Research and Development Authority.

³ “SEIA’s Vision for American Energy Storage,”Solar Energy Industries Association, January 2025.

⁴ Wis. Stat. § 196.491(g).

⁵ While § 196.52(2) is not specifically referring to large electric generating facilities, its definition would likely still apply here. Large is simply referring to the megawatt capacity the facility is operating at.

⁶ “Electricity explained,” U.S. Energy Information Administration, Oct. 31, 2023.

⁷ Bowen, et. al., “Grid-Scale Battery Storage,” National Renewable Energy Laboratory, September 2019.

⁸ ​FAQs: What is the difference between electricity generation capacity and electricity generation? U.S. Energy Information Administration, Feb. 6, 2024.

⁹ For example, conversion of potential energy from a pumped hydroelectric dam often results in a net loss of electricity which was generated from another source. See “Electricity explained,” (discussing pumped hydroelectric storage).

¹⁰ L.1975, c. 68, § 9, eff. Sept. 30, 1975.

¹¹Responsible Use of Rural & Agr. Land (RURAL) v. Pub. Serv. Comm'n of Wis., 2000 WI 129, ¶31, 239 Wis. 2d 660, 619 N.W.2d 888.