- Category 1: 20 kilowatts (kW) or less
- Category 2: larger than 20 kW, but no larger than 200 kW
- Category 3: larger than 200 kW, but no larger than 1 MW
- Category 4: larger than 1 MW, but no larger than 15 MW
The PSC has published two sets of standard forms for interconnection, available on the program web site. One set pertains to systems smaller than 20 kW while the second set applies to larger systems up the maximum size of 15 MW. The PSC also maintains a list of utility interconnection contacts on their Distributed Generation web site. The Wisconsin Distributed Resources Collaborative (WIDRC) has published a set of interconnection guidelines that offer some additional details on the interconnection process.
Generally speaking, Wisconsin's interconnection requirements become more stringent as the system size increases. The rules apply to all public utilities. The 20-kW dividing line between Category 1 and Category 2 installations corresponds to the maximum individual system capacity allowed under the state's net-metering rules. Systems that qualify for net metering are not considered commercial ventures that require commercial liability insurance.
Minimum liability insurance of at least $300,000 per occurrence is required for systems 20 kW and smaller (Category 1) with higher amounts for larger systems based on the category of review under which they fall. However, the law also permits applicants to prove financial responsibility using a negotiated agreement with the utility in lieu of the insurance requirements. Additionally, Category 2-4 facilities must name the utility as an additional insured party in the insurance policy.
Application and study fees vary by category, but systems 20 kW and smaller are not required to pay any fees for application reviews, engineering reviews, or distribution system studies. Facility owners are permitted to file an appeal with the PSC if they believe they are being held to unreasonable requirements, but the rules provide do not provide any guidance on how such appeals will be addressed. In practice, such an appeal would be addressed as a complaint under s. 196.26, Wis. Stats.