Your utility is the city, so the state rules are not yours
Illinois requires investor-owned utilities to offer net metering under Illinois Commerce Commission rules, and ComEd and Ameren Illinois are the two providers that framework covers across most of the state. Naperville Electric Utility is neither. It is owned and run by the city, so the ICC net metering requirement does not reach it.
That does not mean there is nothing available to you. It means the terms are the city's own and cannot be inferred from what a ComEd customer in the next town gets, or from what another Illinois municipal utility offers its customers. Two municipal utilities in the same state can run completely different programs, and copying one city's terms onto another is a common error in solar sales material.
So before you accept any payback figure, get the current terms from Naperville Electric Utility directly: whether it offers net metering or another form of credit for exported power, what it pays and on what basis, what system sizes it allows, and what its interconnection process requires. An installer who quotes you a state-wide rule for a Naperville address is quoting the wrong utility.
Permits, and roughly ten days
The city's own solar checklist puts the permit turnaround at about 10 days. That is a usefully specific number, and more than most Illinois cities publish, but treat it as the review step rather than the whole project: design, utility interconnection and inspection each have their own timing.
Ask your contractor what a recent Naperville job has taken end to end and what the submission package needs to contain. Ask also who is responsible for filing, and who books the inspection. Where a homeowner assumes the contractor handles a step and the contractor assumes the reverse, the project simply sits.
It is worth seeing the application package before it goes in. It defines the system that gets approved, so a change to the array after approval means resubmitting, and that is avoidable rework rather than a cost anyone absorbs quietly.
The Historic District adds about three weeks and a notice
If your home is in Naperville's Historic District, a Certificate of Appropriateness from the Historic Preservation Commission is required under Municipal Code Section 6-11-8:2.15 before solar panels visible from a public street can be installed on a principal structure. The process runs about three weeks and requires mailed and posted notice to neighbouring property owners.
Two things follow from the wording. The trigger is visibility from a public street on a principal structure, so placement is part of the question rather than a detail to settle later: a rear plane or a secondary structure may change what is required. And the notice requirement means neighbours will know, which is a reason to have the conversation yourself rather than let a posted sign do it.
Three weeks is not long, but it is sequential with everything else. Build it into the schedule at the start rather than discovering it after a design has been paid for.
Roofs here, and what they produce
Single-detached houses are 62.8 percent of Naperville's 57,135 housing units, so most residents control the roof and the decision. Single-attached townhouse-style units are 12.2 percent, and those can still carry an individually owned roof section, which makes establishing exactly what you own the first step rather than an afterthought.
The rest is spread thin: 3.6 percent in three and four unit buildings, 7.1 percent in buildings of 5 to 9 units, 5.2 percent in buildings of 10 to 19, and 7.8 percent in buildings of 20 or more. In all of those the roof belongs to the building owner or the association, and a resident cannot commission an installation alone.
On production, plan on roughly 1,262 kWh a year for every kW installed. The estimate comes from satellite irradiance data with a standard performance ratio applied, so it is a screening figure. Orientation, pitch, shade and the usable area left after vents and setbacks decide what a particular roof does, and a quote should show all of it modelled plane by plane.
Incentives, and one that no longer exists
The 30 percent federal residential tax credit under Section 25D applied through December 31, 2025 and is not available for a purchased home system placed in service after that date. A 2026 purchase in Naperville cannot claim it, so any quote or online calculator that still includes it produces a payback figure that is wrong by a wide margin.
If you use a lease or a power purchase agreement rather than buying, the provider may still claim the business version of the credit under Section 48E and pass part of that value through in the rate. Ask the provider what they claim and how much reaches you, and confirm with a tax advisor.
Illinois Shines, the state Adjustable Block Program, works through Approved Vendors who receive Renewable Energy Credit payments and may pass the value on as reduced project cost. Ask any vendor for their Disclosure Form showing how much they are passing on, and because your electricity comes from a municipal utility rather than an investor-owned one, ask the vendor to confirm in advance that a Naperville address qualifies rather than assuming it does.