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Your Illinois Solar Credits Can Expire in October — Check Which Date Your Installer Picked

Ryan Cook•August 18, 2026•Updated Sep 13, 2026

If you had solar installed in Illinois before 2025, there's a date sitting on your utility account that you probably never chose and have likely never seen. It decides whether the credits your panels bank all summer survive into winter or get wiped to zero. For a lot of Central and Southern Illinois homes, that reset lands in October — about a month out.

Here's the part that bothers me: nobody tells homeowners this. It lives in tariff documents.

The rule, in the utilities' own words

Ameren Illinois' net metering tariff, Rider NM2, defines the clock like this: an Annual Period is "the period of 12 consecutive monthly Billing Periods ending on the last day of either the net metering Customer's April monthly Billing Period or its October monthly Billing Period, whichever was selected by the Customer in connection with its application for net metering."

And then, a few sheets later: "Unused credits will expire at the end of the Customer's Annual Period."

ComEd runs the same structure. Its net metering FAQ says kWh net metering credits "do expire and reset annually in April or October as specified on the Net Metering Election Form for customers with legacy status and Fixed Pricing."

Two utilities, same deal. Your extra kilowatt-hours roll month to month, and then once a year whatever's left goes away.

Who this actually applies to

This is a legacy-customer problem, and that word has a specific meaning here.

Connected on or after January 1, 2025? You're fine. ComEd states directly that credits, kWh or monetary, don't expire for customers who interconnected on or after that date. Nothing below applies to you.

Interconnected before January 1, 2025 on a standard fixed-price supply rate? You're a legacy customer. Your credits reset every year.

There are wrinkles inside that. ComEd legacy customers on Hourly Pricing hold monetary credits that don't expire. Ameren customers who move from a fixed rate to Power Smart Pricing lose stored credits entirely in the switch, according to Citizens Utility Board — worth knowing before anyone talks you into a rate change.

Legacy status does come with a real advantage. Legacy households earn credits against all three parts of the bill: supply, delivery, and taxes and fees. Customers who came in after the change are credited on the supply portion only. So the annual expiration is the cost of a better credit, not a penalty on its own.

Why October is the wrong date for a solar house

The two options exist because net metering covers wind too, and the two technologies bank surplus at opposite ends of the year.

CUB spells it out: April is best for solar because it gives you the most time to use credits built up from the previous summer, and October suits wind, which produces more in winter.

Think about how your own system behaves. May through September your panels overproduce, and the bank fills. Then the days get short, the furnace fan runs, and you draw that bank down through winter. An April reset lets that entire cycle finish before the meter zeroes.

An October reset cuts you off right when your bank is fullest.

I've seen this get picked wrong. Not maliciously — a form gets filled out fast, a box gets checked, the homeowner signs a stack of paperwork and never revisits it. The system produces fine. Nobody notices anything is off, because a credit that quietly disappears doesn't show up as a charge.

Go find out which one you have

One phone call. Ask your utility which Annual Period is on your account, and how many banked credits you're sitting on right now.

ComEd: 1-800-825-5436 (net metering questions) or Interconnect@ComEd.com (legacy-status questions)
Ameren Illinois: renewablesillinois@ameren.com

If the answer is April, you can stop reading and enjoy your evening. If it's October, ask whether the date can be changed, and find out what your balance is — that number tells you whether you're about to lose anything worth caring about. A house that burns through its credits over a hot Illinois summer may have nothing banked at all.

Say you do have a meaningful balance and can't move the date this year. Then the honest options are limited but real: run the heavy loads you were going to run anyway before the reset, or look at whether storage makes sense going forward. Illinois pays a $300 per kilowatt-hour storage rebate, and ComEd has confirmed that taking the DG rebate for storage doesn't cost you legacy status — unlike the generation rebate, which does.

My take

The rule itself isn't unreasonable. Utilities aren't obligated to bank surplus forever, and the annual reset is a normal feature of one-to-one net metering.

What I don't love is that the choice between April and October gets made during a sales process, by someone who isn't going to be around in five years, on behalf of a homeowner who's never heard the phrase "Annual Period." It's a small decision with a compounding consequence, buried in a form.

It also argues for something I tell people constantly: a system sized to your actual usage beats an oversized one. CUB makes the same point — the utilities won't require you to match your generation to your usage, but unused credits expire, so matching your household's demand is still the economical move. Overbuilding to chase export credits was already a weaker play after Illinois changed net metering in 2025. A credit that expires unspent is worth nothing at all.

If you're shopping now rather than fixing an old account, this is one more reason the design conversation matters more than the panel brand. Whether you buy or lease, sizing should follow your bill. On the lease side, Illinois pricing currently starts as low as $0.10 per kWh with the rate schedule written into the contract before you sign, so what you pay is predictable from day one. And with rates set to change again this October, it's a reasonable moment to look at the whole picture.

Want help reading your own setup, or figuring out whether a battery earns its keep at your house? Run the numbers on the savings calculator, read the full incentive breakdown, or just call me at (618) 217-2001. You can also reach out here.

Tariff language above is quoted from Ameren Illinois Rider NM2 (Ill. C.C. No. 1) and ComEd's published net metering FAQ (December 2025 edition), re-checked September 2, 2026. Rebate and savings figures are estimates, not promises — confirm your own account details with your utility.

Frequently Asked Questions

It depends entirely on when your system was interconnected. If you connected on or after January 1, 2025, your credits do not expire. ComEd's own net metering FAQ states that net metering credits, whether kWh or monetary, do not expire for customers who interconnected on January 1, 2025 or later. If you connected before that date, you have what the utilities call legacy status, and on standard fixed-price supply your unused kilowatt-hour credits do expire once a year. Ameren's Rider NM2 tariff says unused credits will expire at the end of the customer's Annual Period. That Annual Period ends with either your April billing period or your October billing period, whichever was selected when the net metering application was filed. Most homeowners never made that choice themselves. An installer filled out the form, and the date has been sitting on the account ever since.

Call your utility and ask which Annual Period is on your account. That is the fastest route, because the answer lives in your net metering enrollment record rather than on your monthly bill. For ComEd, the net metering line is 1-800-825-5436, and legacy-status questions go to Interconnect@ComEd.com. For Ameren Illinois, email renewablesillinois@ameren.com. Ask two things specifically: whether your Annual Period ends in April or October, and how many banked kilowatt-hour credits are currently sitting on the account. The second number tells you whether this matters to you at all. Plenty of Illinois homes use up their credits through a hot summer and never bank enough to lose any. If you still have your original interconnection paperwork, the choice appears on the net metering application or, at ComEd, on the Net Metering Election Form. Checking takes one phone call and could be worth real money.

For solar, April is the better choice, and it isn't close. Citizens Utility Board puts it plainly in its Illinois net metering fact sheet: an April expiration date is best for solar installations because it gives you the most time to use credits built up from the previous summer. October is the right pick for wind, since turbines produce more in winter and an October reset gives that owner the longest runway to spend winter credits. The logic follows production. Your panels bank their surplus from roughly May through September, and you spend it back down through winter heating and shorter days. An April reset lets that full cycle finish. An October reset cuts it off right as the bank hits its high point for the year. If your account is set to October and your system is solar, ask your utility whether the date can be changed.

Taking the Distributed Generation rebate for generation costs a legacy customer their legacy status. ComEd states that customers with full retail rate net metering will lose legacy status if they elect to take the DG Rebate for generation, and that legacy status is not affected if a customer elects to take the DG Rebate for storage. That distinction matters. The storage rebate does not put your legacy status at risk, while the generation rebate does. Losing legacy status is not purely a downside, either. Legacy customers earn credits against all three sections of the bill, supply, delivery, and taxes and fees, while post-change customers are credited on the supply section only. But once you are off legacy status, the annual expiration stops applying to you. Whether the rebate is worth that trade depends on your system size, your usage, and your bank of credits, so run both scenarios before deciding.

It is worth pricing out, especially if your Annual Period ends in October. A battery keeps surplus daytime production on your property instead of sending it to the grid and hoping you can spend the credit before the reset date arrives. That turns a credit with an expiration date into stored electricity you control, and it keeps your fridge and furnace running during an outage. Illinois also pays a storage rebate at $300 per kilowatt-hour through both utilities, and ComEd has confirmed that taking the DG rebate for storage does not affect legacy net metering status. Batteries are not free, and I would not tell anyone to buy one purely to dodge a credit reset. But if you are consistently banking more credits than you can spend before April or October, that surplus is telling you something about how your system and your usage line up. Estimated savings vary by home.