On a commercial electric bill there are two very different numbers. One is energy — the total kilowatt-hours you used, like miles driven. The other is demand — your single highest sustained draw, usually measured over a 15-minute window, like your top speed. For many commercial and industrial sites, the demand charge is 30–70% of the bill, and it is the part new load makes worse.
What actually sets your demand charge
The meter records demand in short intervals across the month. The utility takes the highest one — your peak — and bills it at a $/kW rate that can run from a few dollars to well over twenty. A single coincident spike, even for fifteen minutes on one afternoon, can set the charge for the entire billing period. That is why two sites using the same total energy can have very different bills: the one with the spikier load pays more.
Why new load makes it worse — and how much
Add EV chargers, refrigeration, or production equipment and you risk two things at once: a higher peak (a bigger demand charge every month) and less headroom before the service limit. A bank of Level 2 chargers that all start at 5 p.m. — right as the building’s existing peak hits — can stack a new spike directly on top of the old one. The fix is rarely “use less”; it is “do not coincide.”
The measured moves that bring it down
- Stagger and schedule flexible load. EV charging is the most controllable. Spreading or delaying sessions so they avoid the building peak can cut both the demand charge and the headroom hit. See managed EV charging with OCPP.
- Cap the flexible peak. A soft economic cap holds the controllable load below a setpoint so it never sets a new monthly peak.
- Know the named line before you act. Find the kW that is actually setting the charge, what time it happens, and which equipment contributes — then target that window specifically.
Demand and capacity are the same data
The interval data that reveals your demand charge is the same measured-demand record that proves how much load a site can add. That is the useful part: one set of evidence answers two expensive questions — “why is my bill high?” and “can this site take more load without an upgrade?” Read how to avoid a service upgrade for the capacity side.
How Ampscale helps
Ampscale reads your bills and interval data into a Site Power Record that names the demand line — the kW, the dollars, the window — alongside the measured headroom. You see the managed move that cuts the charge and the proof a reviewer needs, in one place. Get a first-pass read with the free calculator, or start a free capacity check.
This is general information, not engineering, tariff, or legal advice. Rate structures and demand-charge definitions vary by utility and tariff; confirm yours on your bill or with your provider.