Demand Charge

Electricity bills can price two different things: energy charges reflect how much electricity a site uses over time, measured in kilowatt-hours, while demand charges reflect a defined measure of the rate at which it draws power. If many machines start together for a short interval, the site's power demand may spike although total monthly energy changes little, and a demand charge turns that interval into a financial matter.

A meter typically measures use over intervals rather than an instantaneous spike, and the US Energy Information Administration notes that demand intervals are often 15, 30 or 60 minutes. An illustrative tariff might charge $30 per kilowatt of monthly billing demand, so at 500 kilowatts that component is $15,000.

"Billing demand" can differ from the current month's highest reading, since a ratchet can use a share of a previous peak, and lowering this month's actual peak might not immediately lower the billed amount. The US Department of Energy describes several structures, including non-coincident demand, time-of-use demand, system-peak charges and look-back methods, so read the site's live rate schedule.

Some demand rates apply only in specified hours, so a site can shift equipment to another time band only if the tariff and operating requirements support it, and moving a peak rather than reducing it may or may not help. Other charges can depend on contribution during a grid-wide peak, which the customer may not know in advance.

An electricity audit should first identify whether the account even has a demand charge, because a business with only a simple energy charge will not save demand fees by staggering equipment. Obtain meter interval data, mark the highest periods and compare them with production, HVAC, charging and refrigeration schedules, since the shape of demand often reveals which process needs investigation.

Staggering equipment starts may reduce simultaneous draw, but test the operational effects before changing controls. A sudden spike might come from an unusual operating event or a metering issue, so reconcile the interval with the bill instead of dismissing a short peak because average use looks normal.

Battery storage may discharge during a peak, but installation and controls cost money, so a projected saving needs the tariff, battery efficiency, maintenance and useful life rather than a generic example. Pre-cooling a building is another possible tactic that shifts electricity use and relies on the building's thermal behaviour, so comfort and total energy effects should be measured rather than assumed.

A plant that cuts energy consumption may still pay a high demand charge if its maximum draw is unchanged, which is why managers should track monthly maximum kilowatts, billed kilowatts, total kilowatt-hours, rate and tariff period together. Seasonal schedules also matter, as a cooling peak in summer and a production peak in winter may have different rates, so compare like months and identify rate changes before claiming an operational gain.

For an invented factory whose morning machine starts create a 500-kilowatt interval maximum, test staggered starts and read the billed-demand rule before forecasting savings, since a ratchet may delay benefits. Demand charges are not automatically a penalty for waste, because they reflect the capacity a tariff assigns to the account under its rules, and the practical sequence is to read the rate schedule, inspect interval data, then test feasible changes.