The capacity auction just repriced Illinois electricity

I.How the auction actually works

PJM runs a capacity market called the Reliability Pricing Model. Once a year it holds what it calls a Base Residual Auction for a future delivery year, and power plants, demand response (customers paid to cut usage on command), and some batteries offer to be available on the grid's worst days. PJM buys enough of those promises to meet a reliability target plus a cushion, and the price that clears is quoted in megawatt-days, meaning one megawatt of promised capacity held ready for one day.

You never bid in this auction, but you pay for it. The amount of capacity ComEd must buy is tied to how much power its customers pull on peak days, and that cost rides inside the supply charge on your bill. So when the clearing price rises, the capacity piece of the bill rises with it, usually on a delay set by the delivery-year calendar rather than all at once.

II.Reading the latest results

The auction for the 2025/2026 delivery year cleared at roughly $270 per megawatt-day across most of PJM, up from under $30 the year before, per PJM's own auction report. The next one, for 2026/2027 and held in the summer of 2025, cleared higher still, on the order of $329 per megawatt-day, close to a price cap that federal regulators had approved. Treat both figures as the latest public numbers, not final truth, because PJM revises and restates results.

Why the jump? Demand is climbing, pushed by new data centers and the slow electrification of heat and cars, while older plants retire faster than new projects finish connecting. PJM and its independent market monitor have pointed to that tightening supply. The honest answer on how long high prices last is that it depends on how quickly new generation and storage clear the interconnection queue (the waiting line to plug into the grid).

III.Who pays more, and how much

Here is the honest math. Capacity is one slice of your bill, not the whole thing, so a large percentage jump in the auction price turns into a smaller percentage on the total. Capacity is often on the order of a tenth of a typical residential supply cost, and the exact dollars depend on your usage and the delivery-year schedule. ComEd passes the auction cost through to customers; it does not pocket the clearing price.

Map the players and it gets clearer. PJM runs the auction, the Federal Energy Regulatory Commission approves the rules it must follow, and the Illinois Commerce Commission oversees ComEd's rates inside the state. Note that this is the PJM side of Illinois only: most of central and southern Illinois sits in a different grid called MISO, with its own separate process, so a downstate reader's bill moves on a different clock.

IV.Worth watching this month

1. Watch PJM's auction information pages for the parameters of the next Base Residual Auction, which quietly set the stage for future prices and are routine to post but worth reading.

2. Watch the Illinois Commerce Commission docket calendar for any ComEd rate proceeding where capacity pass-through costs surface, since that is where the number meets your actual tariff.

3. Watch FERC for any order touching PJM's price cap or market rules, because a rule change there can move future auctions more than any single bid.

4. Watch your own ComEd supply charge over the next few billing cycles and compare it to last year, which is routine for most households but easy to check.

5. Watch Springfield for any proposal to change how Illinois takes part in PJM's capacity system, a possibility that is still early, contested, and far from certain.