Signing a contract with a solar installer does not mean your system can turn on. Before that happens, ComEd or Ameren Illinois has to approve something called interconnection, the formal process of connecting your system to the utility's grid. This is a separate question from how your exports get credited once you're live. For that, see Net Metering in Illinois: How Solar Credits Work with ComEd and Ameren. This article is about the approval process itself: what ComEd and Ameren each require, roughly how long it takes, and what tends to slow it down.
Interconnection is a permission step, not a credit calculation
Interconnection is the utility's review of whether your system can safely connect to its grid, and its formal authorization once that review is satisfied. Only after that authorization, called Permission to Operate (PTO), can your system legally run and start generating the exports that net metering credits. A signed installation contract, a completed roof install, and even an inspected electrical system are not the same as PTO. Until the utility issues it, your system should not be energized for grid-connected operation.
How ComEd's process works
For a typical residential system, your installer submits an interconnection application to ComEd using the appropriate form: Level 1, Level 2, or Level 4, depending on system size and equipment type. According to ComEd's own net metering program materials, wind and inverter-based solar systems of 25 kilowatts or less qualify for Level 1 expedited review, which ComEd states takes approximately three weeks after a complete application is received. Most residential rooftop systems fall well under that 25 kW threshold.
A separate net metering application is not required if you specify your intent to generate on the interconnection application itself. Once approved, your account moves onto Rider POGNM, ComEd's net metering tariff, but only once three things have happened: ComEd has approved the interconnection, you've submitted a Certificate of Completion (required under Illinois Administrative Code Title 83, Part 466) and ComEd has countersigned and returned it, and you've met the remaining service prerequisites under Rider POGNM. Skipping or delaying any one of those keeps you out of PTO, even if your panels are physically installed and ready.
If you're buying a home with an existing solar system already connected to ComEd, you don't need a new net metering application. Instead, ComEd requires a DER Facility Assignment Form, due within 60 days of taking service at that address, or net metering terminates on the account.
How Ameren Illinois's process works
Ameren handles interconnection applications through PowerClerk, its online application management system. Your certified installer typically submits the application on your behalf, and you'll get email status updates as it moves through review. Before your system can legally operate, Ameren likewise requires an approved interconnection application and a signed Certificate of Completion.
Ameren's own net metering page confirms residential systems apply under Rider NM (net metering), while larger generating facilities fall under the separate Rider QF tariff instead; a customer cannot take service under both riders at the same time. Which rider applies does not change the interconnection review itself, but it does affect which agreement you ultimately sign once interconnection is approved.
A newer wrinkle, specific to Ameren and worth knowing if your installer is quoting a larger system: effective for applications submitted on or after January 9, 2026, Ameren's DER Bulletin 2026-01 tightened how PowerClerk determines whether an application must be reviewed at Level 2 or escalated to Level 4, based on the system's size relative to the voltage of the line it connects to. For most single-family rooftop systems, sized well under 500 kW, this change doesn't come into play. It mainly affects larger systems and community solar projects interconnecting at higher voltages.
The statewide clock both utilities follow
ComEd and Ameren aren't setting their own internal interconnection timelines; both operate under the same statewide rule, Illinois Administrative Code Title 83, Part 466, which governs how every Illinois utility must handle Level 1 Expedited Review. Under that rule, once your installer submits a complete application:
- The utility has 7 business days to confirm the application is complete, or tell you what's missing.
- If anything is missing, you get 10 business days to supply it.
- The utility then has 15 business days to run the required technical screens and tell you whether your system passes.
- If minor equipment modifications are needed, the utility must send you a standard agreement and cost estimate within 10 business days of your election and fee payment; for more substantial modifications, that window is 15 business days.
- You then have 30 business days to sign and return that agreement, with a possible 15-business-day extension if you ask for one.
That's the regulatory floor, not a guarantee of ComEd's three-week estimate above; a straightforward 25 kW-or-under application that passes its screens cleanly can move faster than an application that needs a modification agreement worked through step by step.
What actually slows this down
In practice, delays tend to come from the same handful of places: an incomplete application (missing equipment specs, an unsigned form, a missing invoice or installer certification number), a system that doesn't pass Level 1 screens cleanly and gets kicked into a longer Level 2 or Level 4 review, or a Certificate of Completion that sits unsubmitted after the physical install is finished because nobody circled back to file the paperwork. None of these are complicated to avoid, but they do require someone, you or your installer, actually tracking the step after the panels go up.
Questions to ask your installer before you sign
- Is this a Level 1, Level 2, or Level 4 application for my system, and why?
- Who is responsible for filing the Certificate of Completion once installation is done, and how will I know it's been submitted?
- What's the realistic timeline from application to Permission to Operate for a system my size, not just the install date?
- If I'm moving into a home with solar already connected, has the DER Facility Assignment Form been handled?
A good installer should be able to answer all four without hesitation. If an installer's timeline for "going live" skips interconnection and PTO entirely, that's worth asking about directly.
Where this fits with everything else
Interconnection approval and net metering crediting are two different systems that happen to run on the same utility account. This article covers the approval gate; Net Metering in Illinois covers how your exports get valued once you clear it. For the utility-specific pages on what else to expect as a ComEd or Ameren customer, see Solar for ComEd Customers and Solar for Ameren Illinois Customers, or the broader Illinois solar hub and Illinois solar incentives pages. If you're still comparing installers, How to Choose a Solar Installer in Illinois has questions worth asking before you sign anything.
Ready to see what a qualified local installer would quote for your home? Start your free, no-obligation solar assessment and ask directly how they handle interconnection timing for a system your size.
Frequently asked questions
Can my system be turned on before Permission to Operate?
No. ComEd and Ameren both require PTO, which depends on an approved interconnection application and a countersigned Certificate of Completion, before your system should be energized for grid-connected operation.
Does a Level 1 application mean ComEd's three-week estimate applies to everyone?
It applies specifically to inverter-based wind and solar systems of 25 kW or less that qualify for Level 1 expedited review. A system that needs Level 2 or Level 4 review, or one that doesn't pass its initial screens, follows a different and generally longer timeline under Illinois Administrative Code Part 466.
Does Ameren's January 2026 bulletin affect a typical home rooftop system?
Usually not. It changes how larger systems and certain community solar applications get classified by voltage and size; most single-family rooftop systems stay well under the thresholds it addresses.
Who actually files the paperwork, me or the installer?
Your installer typically submits the interconnection application and the Certificate of Completion on your behalf, but confirm this directly. Start your quote and ask a prospective installer to walk through exactly who files what, and when.
