I.How the price reaches your meter
Northern Illinois sits inside PJM Interconnection, the regional grid operator that runs the wholesale market for a stretch of the country from Chicago to the mid-Atlantic. Every hour PJM calculates what it costs to serve the next unit of demand at a given point on the grid, a figure called the locational marginal price (the market price of electricity at a specific spot, set by the most expensive plant needed to meet demand there). Hourly Pricing passes a version of that price through to the household, with a few small market adjustments, instead of the flat supply rate.
Only the supply portion of your bill changes. The charges for delivery, the poles and wires ComEd owns and maintains, stay on their regular schedule, as do the state and local taxes and the fixed monthly customer charge. So the swing a household on the program feels is real but bounded: it rides on roughly the supply half of the bill, not the whole thing. On most hours of most days the wholesale price sits below the flat rate; the risk lives in a handful of hot afternoons when it can spike well above it.
II.The honest math
Savings on Hourly Pricing come from one thing: moving electricity use away from the expensive hours. In a Chicago summer the costly window tends to fall in the late afternoon and early evening, when air conditioners across the region run hardest and the grid leans on its most expensive plants. A household that can shift the dishwasher, the laundry, and an electric vehicle charge into the night, and that can pre-cool the apartment before the peak, has a real shot at paying less over a year than it would on the flat rate.
A household that cannot shift much gets a weaker deal, and may do worse. If someone is home all day running cooling in August, or depends on equipment that cannot wait for a cheaper hour, the flat rate's predictability is worth something. The program sends alerts when it expects prices to run high, which helps, but it cannot move the load for you. Anyone uneasy with a bill that changes shape from month to month should weigh that discomfort honestly before switching.
III.Checking the price before you commit
The prices are public, and a reader can watch them without enrolling. The program's site posts the next day's hourly prices in the afternoon and updates the live price through the day, so you can track for a week or two what a kilowatt-hour would have cost in your own waking hours. Enrollment is free, there is no contract that locks you in, and a household can return to the flat rate if the experiment does not suit it, though switching back may take a billing cycle or two to take effect.
Before enrolling, the honest step is to look at your own week. Pull a recent bill or the usage view in your online account and ask when the power actually gets used: if most of it already lands in the evening and overnight, the program may fit; if the house is busiest from four to seven on summer afternoons and nothing about that can move, it probably does not. ComEd and the program administrator publish comparison tools that estimate how a past year on the flat rate would have looked on hourly prices, which is a better guide than any general rule.
IV.Worth watching this month
1. ComEd resets its flat supply rate (the 'price to compare') on a set schedule, roughly twice a year, so watch for the next posted rate, since the gap between it and wholesale prices is what the whole decision turns on.
2. Watch PJM's real-time prices during the first real cold snap, because an Illinois polar-vortex morning can push the expensive hours into the early morning rather than the usual summer late afternoon.
3. On the first sustained hot stretch, the program site's day-ahead prices will show how high the late-afternoon peak runs, a routine posting but the clearest real-world test of the program.
4. Keep half an eye on Illinois Commerce Commission filings touching ComEd's supply and rate design, mostly routine, but a change there shifts the flat rate that hourly pricing is measured against.
5. If you are curious, note when the program administrator opens its next outreach or enrollment push, which is routine and nothing to rush.