Commercial meters can bill the highest short power draw on its own line, apart from the kilowatt-hours. That line is the demand charge. Energy is what the building used across the billing period. Demand is the peak the tariff's interval caught. A battery bought to shave that peak has to be chosen in kilowatts, for the height you intend to cut, and in hours, for how long that height lasts. A storage quote that names only kilowatt-hours has not answered the demand question.
Two lines, two units
The energy line moves with kilowatt-hours. Solar used inside the building, and a battery that shifts midday energy into a later hour, both act on that line. The demand line moves when the highest short draw changes. A battery held full for outages never touches a peak it does not discharge into. The operating mode is part of the size. Power, energy, and duration — duration being energy divided by power — are the words on the commercial energy storage page. Use them the same way here.
A time-of-use rate prices the hour. A demand charge prices the peak. Both can sit on one bill, and they are different lines. The hour-based case for a house battery is in time-of-use rates and a home battery. Net metering credits exported energy under that tariff's rules. It does not define a demand charge.
| Line | What moves it | What a battery can change |
|---|---|---|
| Energy, in kilowatt-hours | How much electricity the building uses over the period | On-site solar, or stored energy released while the building would otherwise buy |
| Demand, in the unit the tariff prints | The highest short power draw the meter records | A discharge that covers that peak for as long as the peak lasts |
Kilowatts and hours together
Suppose, only as arithmetic, that you want to cut 10 kilowatts from a peak that lasts one hour. The battery has to deliver 10 kilowatts, and it has to have 10 kilowatt-hours available for that hour before conversion losses. Stretch the same 10 kilowatts to two hours and the energy doubles. Shorten the peak to a brief spike and the energy shrinks while the kilowatt number stays put. Nothing in that pair is a survey of warehouses, a utility average, or a quote. Your meter history replaces it.
The interval length is whatever the tariff prints. This page will not assign one interval to every commercial meter. Some tariffs add a ratchet that carries part of an earlier peak onto later bills. When that clause exists, a peak you missed can echo. When it does not, only the current period's peak is on the line. Read the unit as well. Some meters bill kilowatts. Some bill kilovolt-amperes. The battery discharges real power. If the bill is in kilovolt-amperes, a watt of discharge and a unit of billed demand are different quantities. Ask which unit the tariff uses before anyone models the shave.
When the discharge has to land
The spike and the discharge have to overlap. A plant that peaks at dawn, and a battery scheduled like a house that only empties at dinner, are on different clocks. Write down the hour the peak actually occurs, from the bill or the interval data, and discharge then. Self-consumption and an export limit change how solar is used or refused at the meter. They do not replace a demand calculation.
A tariff with no demand line will not yield a demand saving, because the line is absent. Houses whose tariff cares about the hour belong on the time-of-use page. Payback arithmetic that can hold a battery's job is in how a solar payback period is calculated. Any figure there that is not from your tariff stays labeled hypothetical. There is no dollar-per-kilowatt rate on this page to paste into that sheet. Bring the tariff.
