Does Ameren Illinois Have Peak Hours, and Do They Cost Your Business Anything?

"Peak hours" is one of those phrases that sounds like it must cost you something. Often it does not, and the difference is not about when you use electricity. It is about whether any charge on your bill is defined by a window of hours.

That is a question you can settle from documents you already have, before spending anything on rescheduling production or on equipment sold to shift load out of an expensive window.

The three different things "peak hours" can mean

They are frequently confused, they carry very different amounts of money, and only one of them is usually worth reorganizing an operation around.

A time-of-use energy price. The per-kilowatt-hour price is higher during defined hours. Moving consumption out of the window saves the price difference on the kilowatt hours you moved. The saving is real and usually modest.

A demand window. A charge in dollars per kilowatt is applied to your highest measured demand, but only demand recorded inside a defined window counts. This is the expensive one, because a single half hour can set the whole charge, and because everything outside the window is free of it.

A marketing phrase. Utilities and program vendors both use "peak hours" loosely to describe when the grid is busy. That is a fact about the grid and not a charge on your bill.

If your bill has no charge defined by a window, then peak hours are a fact about the grid and cost you nothing directly.

What we know here and what we do not

We reconstruct ComEd commercial bills from the interval record and reconcile them to the cent. We have not reconciled an Ameren Illinois bill.

So we will not tell you Ameren Illinois's window, its determinant, or its rates. What we can do is show you how much a window can be worth in a territory where we have checked, and give you the four questions that settle it for your own account.

In ComEd's standard commercial delivery classes, billed demand is the highest half hour recorded during weekday daytime hours, in a window running from 9 a.m. to 6 p.m., with nothing carried forward from a prior month. Those properties are reconciled against real bills. Two of them do enormous work: everything overnight and at weekends is outside the window, and one bad month costs one month.

Neither property is universal. A tariff that measures demand across all hours makes overnight load expensive. A tariff that carries a prior peak forward makes one bad afternoon expensive for a year. Both structures exist elsewhere, and whether either exists on your account is a question about your rate schedule.

The four questions that settle it

All four are answerable from your bill and your filed rate schedule.

1. Is there a charge priced in dollars per kilowatt? Look at the delivery portion of the bill. If every line is priced per kilowatt hour or is a flat monthly amount, no window is charging you for demand and the expensive case does not apply.

2. If there is one, over what window is the quantity measured? The rate schedule defines this. Ask for it in the form of hours, days of the week, and months of the year, because all three are commonly restricted and each restriction is money.

3. Over what interval length is demand measured? Fifteen minutes and sixty minutes produce different billed numbers from the same operation, and the shorter the interval the more a brief surge costs you.

4. Does anything carry forward? A ratchet provision sets a floor under future billed demand based on an earlier peak. If one exists, preventing a single spike is worth many times more than if one does not.

Your utility representative can answer all four, and the filed rate schedule is public at the Illinois Commerce Commission.

What to do once you have the answers

If there is no demand window, stop here. Rescheduling to dodge peak hours buys you the energy price difference and nothing more, and that is a smaller number than most people expect.

If there is a demand window, the next question is the one that decides whether anything can be done: how far your highest qualifying interval sits above your second highest. Remove the top one and the next becomes your billed demand. Your saving is that gap, not the size of what you removed, and almost no proposal you receive will contain the gap.

That number comes out of your interval record, which is the same input we use in ComEd territory and the reason a reconstruction beats an estimate. If your operation is a candidate, establishing the gap is the cheapest useful thing you can do next.