Why ComEd's electricity supply rate keeps moving

ComEd's price to compare changed on October 1, dropping from 10.399 to 10.103 cents per kWh. Despite the small drop, the rate is still up more than 50% since May 2025, when it was 6.552 cents.

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What the price to compare is

The price to compare is ComEd's rate for the electricity supply portion of the bill, the part customers can shop for. Customers who do not choose an alternative supplier pay it. Suppliers list their offers on Plug In Illinois (https://plugin.illinois.gov/your-available-choices/offers.html?said=1), the shopping site run by the Illinois Commerce Commission, which also explains the price to compare and publishes its monthly history (https://plugin.illinois.gov/understanding-the-price-to-compare/price-to-compare-comed.html).

The price to compare has two parts: the electricity supply charge, which usually changes in June and October, and the transmission services charge, which usually changes in January. ComEd supply customers also pay a third line that sits outside it: the Purchased Electricity Adjustment, or PEA, which changes every month and can move their total supply cost up or down by several cents per kWh.

What drives the changes

ComEd is unusual among utilities in states with supplier choice in who carries the risk that customers use more or less electricity than planned. In most other choice states, including nearby Ohio and Pennsylvania, the utilities hold auctions in which large energy companies bid to supply a share of the utility's customers. The winners supply whatever those customers actually use, hour by hour, at the price they bid, so the winners carry the risk that a heat wave or a cold snap pushes usage, and market prices, above plan. In ComEd's territory, that risk falls on ComEd's own supply customers, through the PEA.

Illinois, through the Illinois Power Agency (IPA), does things differently. Instead of auctioning that load-following supply, the IPA buys fixed monthly volumes of electricity. The volumes vary by month to follow the seasonal shape of demand, but the winning bidders deliver a set amount, not dependent on the amount customers actually use.

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ComEd manages the difference. When its customers need more electricity in a given hour than the IPA bought, ComEd buys the rest from PJM, the regional grid operator; when they need less, it sells the excess. ComEd also pays for the other services PJM requires, such as capacity, transmission, and ancillary services. It estimates all of these costs when it sets the seasonal price to compare.

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Those estimates are never exact, because nobody can predict precisely how much electricity customers will use, or what balancing and the other services will cost. ComEd also does not profit from supplying electricity, and it does not lose money on it either: every cost is passed through to customers. So when ComEd collects less than it spent, it recovers the shortfall in later bills, and when it collects more, it hands the excess back as a credit. The PEA is that settling-up. Each month's PEA reflects costs from three to four months earlier.

The nuclear deal

There is one more wrinkle. The IPA deliberately buys less electricity in its auctions than ComEd's customers will need. Its target for the current year is 50% of expected demand in summer and 30% in the rest of the year.

The reason is a deal Illinois struck in 2021, in the Climate and Equitable Jobs Act (https://ipa.illinois.gov/carbon-mitigation-credit-reports.html), to keep three nuclear plants running: Byron, Braidwood, and Dresden. Power prices had fallen so low that their operator could no longer cover the plants' costs, and closing them would have set back the state's carbon-free energy goals. Under the deal, which runs from June 2022 through May 2027, the plants are guaranteed a set price for their output. When market prices for energy and capacity are below that price, customers pay the plants the difference. When market prices are above it, the plants pay customers the difference.

In effect, the deal covers part of ComEd's supply needs, and it pays off when market prices are high, which is exactly when the unhedged part of ComEd's supply gets expensive. The nuclear credit or charge appears on every ComEd customer's bill, as the "Carbon-Free Energy Resource Adjustment". The PEA applies only to customers who take ComEd's supply. Customers with an alternative supplier are shielded from the PEA but still get the nuclear credits and charges.

So in months when market prices spike, ComEd supply customers tend to see a large PEA charge and a partly offsetting nuclear credit. Customers of alternative suppliers see only the credit.

Watching it play out

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The clearest example is May 2026. Winter Storm Fern sent January's power prices soaring. Four months later, ComEd supply customers saw both sides of it:

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The deal cuts both ways. When prices were low, the nuclear adjustment was a charge: it reached 2.339 cents per kWh in April 2024. Every ComEd customer paid it, including customers with a fixed-price supplier contract. Over the past three years, the PEA and the nuclear adjustment have tended to move in opposite directions. The offset is real, but it is rarely one-for-one, and it arrives on a lag.

October 2026: a credit from a hot July

October's PEA is a credit of 1.551 cents per kWh. It mostly reflects July's heat. Capacity and transmission are fixed daily costs, but ComEd collects them on a per kWh basis, at a rate set based on expected usage. July's heavy air-conditioning use brought in more revenue than those costs, and October's credit hands the excess back.

October's nuclear adjustment is close to zero, a credit of 0.115 cents. The seasonal credit is 1.148 cents, but the monthly true-up swung to a 1.033-cent charge. For much of the past year, the nuclear credits were enlarged by a pass-through of the plants' 2024 federal nuclear tax credits: about $800 million (https://capitolnewsillinois.com/news/high-energy-prices-federal-dollars-turn-nuke-subsidies-into-ratepayer-relief-in-northern-illinois/) reached ComEd customers' bills between November 2025 and May 2026. That refund appears to have run its course: the plants' owner reports little or no tax-credit benefit for 2025 or 2026.

November 2026: a charge from July's prices

November should swing the other way. July's hot weather also brought expensive power, and that cost will reach bills in November. Our estimate is a PEA charge of about 3.8 cents per kWh, partly offset by a nuclear credit of about 2.2 cents, for a net increase of roughly 1.6 cents for ComEd supply customers. Customers with an alternative supplier would see only the credit. ComEd files November's figures by October 20.

What changes in 2027

The nuclear deal ends in May 2027. From June 2027, the IPA's draft 2027 procurement plan (https://ipa.illinois.gov/content/dam/soi/en/web/ipa/documents/20260817-draft-2027-electricity-procurement-plan-ipa.pdf) returns ComEd to the approach used elsewhere in Illinois: buying ahead about 100% of forecast supply, and 106% of on-peak supply in July and August, when heat pushes usage above the average. The PEA will not disappear, since actual usage never matches the forecast exactly, but it should become smaller and less volatile, and the nuclear adjustment goes away. How much ComEd's supply rate moves that June will depend on the auction prices the IPA locks in over the coming months, and on PJM's capacity prices. We will look at both in a follow-up.

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Sources: ComEd Rate BES, Rider PE and Rider CFRA informational sheets (ComEd schedule of rates, filed September 17-18, 2026); Plug In Illinois historical price to compare; Illinois Power Agency procurement results and 2026 Electricity Procurement Plan; PJM metered load and day-ahead prices, ComEd zone; Constellation Energy Q2 2026 Form 10-Q; Capitol News Illinois (April 13, 2026). November figures are Energywell estimates.

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