Commercial Demand Charges in Illinois: What They Are & How to Manage Them

For many Illinois commercial accounts, the demand charge — not the per-kWh supply rate — is where cost concentrates. It bills how hard a facility pulls at its peak, and it responds to different levers than a supplier contract. Understanding it is often the highest-value part of a commercial energy review.

Who this is for

Facilities with demand-billed rate classes and uneven load — manufacturing, warehousing and cold storage, and any operation with large motors, compressors, chillers, or simultaneous equipment starts. If a bill shows a "kW" or "demand" line, this applies.

How demand billing works

The utility measures peak demand (in kW) over a short interval, commonly 15 minutes, during the billing period, and charges for that peak separately from energy. Because it is driven by coincident equipment use, two facilities with identical monthly kWh can face very different demand charges. That is why total energy alone is a poor predictor of a commercial bill.

Demand vs. supply — two different levers

Shopping a supplier changes the supply rate. It does not, by itself, change the utility's delivery demand charge. Managing demand — understanding when peaks occur and whether they can be shifted or flattened — is a separate exercise from procurement, and for peaky loads it can move the bill more than a supply-rate change. A complete review looks at both.

Capacity tags carry demand into future supply cost

In the PJM region that includes ComEd, an account's capacity tag (PLC) is derived from its usage during system peak periods and feeds the capacity component of supply pricing for a delivery year. Peak behavior in a few key hours can therefore affect cost well beyond the current month's demand line. Read the PJM capacity and Illinois business bills guide for how delivery years and PLC interact — and note that a PJM auction clearing price is not a bill rate.

What a demand review needs

Monthly bills establish the demand pattern; interval data is what reveals when peaks occur and whether they are addressable. Reconcile interval data to billed kWh and kW first, then look for recurring peak drivers. Nothing here promises a specific reduction — demand outcomes depend on how a facility actually operates.