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Demand charges explained: kW vs kWh on a commercial bill

Commercial

kW measures peak instantaneous load; kWh measures total energy. Demand charges hit your peak. The 4 strategies to lower demand without lowering output.

Harry Parker

Energy Consultant, Seenra Inc

Commercial10 min readPublished

Featured infographic

kW vs kWh — peak demand vs total energy

kW measures the highest 15-minute draw. kWh measures total monthly energy. Demand charges hit the kW peak; energy charges hit the kWh total.

Open graph image · /og/demand-curve.png

Demand charges are the second-largest line item on most commercial electric bills after energy (kWh) charges. They measure the peak instantaneous kW draw of your facility during a defined 15-minute window. A single peak event can drive the demand charge for the whole month. Four strategies cut peak demand without cutting output: stagger major equipment startup, install battery storage, schedule production around peak hours, install power-factor correction.

The kW vs kWh difference

kW (kilowatt) is a measure of instantaneous power — how hard the facility is drawing right now. kWh (kilowatt-hour) is a measure of total energy — kW times hours.

A facility can have low total kWh but a high single-minute kW peak. The demand charge is set by that single peak, not by the total kWh consumed.

Four strategies to cut peak demand

Strategy 1: stagger major equipment startup so that compressors, motors, and chillers do not all hit peak simultaneously. Strategy 2: install battery storage to discharge during peak windows.

Strategy 3: schedule production around utility peak hours. Strategy 4: install power-factor correction to reduce apparent kW (kVA) at the meter.

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Common questions

Quick answers from the editorial desk

When is the demand window measured?
Most US utilities measure peak demand during a defined window (typically 1 pm to 9 pm weekdays) using rolling 15-minute averages.
What is a ratchet clause?
Some commercial tariffs apply a ratchet to demand charges — billing the customer for a percentage of their highest peak from the prior 11 months, even in low-usage months.
Does a single 15-minute spike really matter?
Yes. Most demand charges are set by the single highest 15-minute draw of the month. One spike from a startup event can drive demand charges for the whole month.
Can battery storage offset demand charges?
Yes if sized correctly. A battery sized to cover the typical peak draw discharges during demand windows and saves $4 to $22 per kW per month depending on tariff.

Further reading

Pillar guide, cluster siblings, and state pages cited above

Sources

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