One interval sets the charge
Most business demand tariffs bill the highest 30-minute interval recorded inside the demand window. There is no averaging across the window or the month: one hot Tuesday afternoon can set the charge.
Battery peak shaving guide
What is peak shaving, and when can a battery do it?
Sometimes. Peak shaving lowers the highest power reading the meter records, so the demand charge set from that reading falls with it. A battery is the cleanest way to do it on a business site—but only if it has the power to cover the gap, the energy to last the peak, and a tariff that charges for peak demand in the first place. This page shows how to size all three from a bill and interval data.
Start with the charge
How the bill records a peak worth shaving.
A demand charge is billed from the single highest reading inside the tariff’s demand window. Four rules decide whether a battery can touch it. If the phrase is new, start with how demand charges work on a business bill and come back.
The window is not all day
The tariff names the hours that count. On Endeavour Energy’s N19, the window is 16:00–20:00 on business days. A peak at lunchtime may cost nothing; the same peak at 6 pm sets the bill.
The maximum resets on the tariff’s rules
Some tariffs reset the billed maximum each month; others hold a ratchet across a season or year. The reset rule decides whether one covered month stays covered.
The charge repeats daily
The demand rate is charged per day of the billing period against the recorded maximum. The same kVA figure is paid for again every day of the month it was set.
The window, interval length and reset rules belong to the assigned network tariff. The NSW tariff guides list the current windows by network and tariff code.
The two numbers that size the battery
Peak power and peak duration decide everything.
Battery brochures quote one capacity figure. A demand charge needs two: how hard the battery can discharge, and for how long.
Power · kW
Covers the height of the peak
Must match or exceed the gap between the control threshold and the raw peak, at the moment the peak occurs.Energy · kWh
Covers the length of the peak
Must sustain that discharge for the longest qualifying peak event in the data, with losses and reserve still to come off.Power covers the gap
The inverter must deliver the difference between the control threshold and the raw peak, at once. A site peaking 50 kVA above its threshold needs at least 50 kW of discharge power—or the meter still records the uncovered top of the peak.
Energy covers the duration
Power that runs out mid-peak is worth nothing. A 50 kW shave held for 90 minutes needs 75 kWh delivered that evening. The longest peak of the year, not the average one, sizes the battery.
Losses and reserves come off the top
Round-trip losses mean the battery imports more than it delivers, and usable capacity is usually below nameplate. A battery asked to deliver 75 kWh through the peak needs meaningfully more than 75 kWh installed.
Every qualifying day needs the same cover
The charge survives one missed peak. The sizing case is built from the worst combination in twelve months of interval data—highest peak, longest duration, longest run of peak days.
A 50 kVA gap, held for 90 minutes
- Interval data shows the raw peak running up to 50 kVA above the intended control threshold, inside the 16:00–20:00 window.
- The longest qualifying peak event lasts about 90 minutes.
- Round-trip losses and usable-versus-nameplate capacity are accounted for before the battery is chosen.
50 kW × 1.5 h = 75 kWh delivered that eveningThe site needs at least 50 kW of discharge power and roughly 75 kWh delivered through the peak—so meaningfully more than 75 kWh installed once losses and usable capacity are counted.
Illustrative only. The real numbers come from twelve months of the site’s own interval data, the worst peak in it, and the assigned tariff’s window and reset rules—not from a brochure capacity figure.
How the battery decides to fire
The control threshold is where peak shaving is won or lost.
A peak-shaving battery watches the meter and discharges when site demand crosses a target set below the expected peak. That one number decides whether the month is covered.
Three ways the threshold fails.
Set it too high and the battery never fires, or fires after the qualifying interval has already been recorded. Set it too low and the battery empties before the peak ends, and the clipped peak re-emerges above the target anyway. Set it against the wrong baseline—a month with mild load, a schedule change, new equipment—and the battery chases a peak that no longer resembles the site’s. The threshold comes from the same twelve months of interval data as the sizing, and belongs in the operating controls, not in a supplier’s default.
Most large-business tariffs bill demand in kVA, not kW. A battery discharging real power may reduce only part of the apparent-power peak, because reactive behaviour counts too. Where power factor is poor, dedicated correction equipment can be the cheaper first action—check before treating the whole kVA charge as battery-addressable.
Worked example · network component only
What a held 50 kVA shave is worth on Endeavour Energy’s N19.
The sizing above, priced. The site’s billed peak falls by 50 kVA, and the reduction holds for the full 30-minute peak interval, every business day of the month.
Cutting 50 kVA from a peak on Endeavour Energy’s N19 tariff
- The site’s billed peak falls by 50 kVA, and the reduction holds for the full 30-minute peak interval.
- 2026–27 network demand rates, GST-inclusive: 58.421 c/kVA/day high season (November–March), 53.163 c/kVA/day low season.
- A 31-day month. Peak window: 16:00–20:00 on business days, set from the highest 30-minute kVA reading.
50 kVA × 58.421 c/kVA/day × 31 days ÷ 100 = $905.53$905.53 less in the network demand component for that month. Held every month, the same reduction is worth roughly $10,100 a year across the seasonal rates.
This is gross, not net: battery cost, charging energy and losses come out of it, and one missed peak can set a new maximum. It is a network rate, not a retail quote—the retailer’s pass-through decides what the bill does. And because N19 bills kVA, confirm how much of the peak is reactive before counting the full reduction.
See the current N19 rates and time windowsWorth checking first
When peak shaving fails.
These conditions do not make the battery useless—but each one can leave the billed maximum, and the charge, untouched.
- 01Peaks longer than the battery. A three-hour peak against a two-hour battery leaves the meter recording a new maximum once the battery empties. Duration, not headline capacity, is the failure.
- 02Peaks with no pattern. A peak that arrives randomly can fire before the highest one and spend the battery early. Reliability, not average performance, is what the charge responds to.
- 03No demand charge to attack. On a flat tariff with no kW or kVA component, shaving the peak saves nothing regardless of how neatly the battery does it.
- 04More peak events than cycles. Two distinct peaks per day inside the window can exceed what one daily charge can cover, especially in winter when solar recharge is thin.
- 05A power-factor problem wearing a battery’s clothes. Where the kVA maximum is inflated by reactive load, correction equipment can fix the bill for far less than a battery. Check what the kVA is made of before sizing a shave.
A failed shave can still be a strong tariff-change, efficiency or power-factor project—the wider set of battery cases and misses is in the battery value guide.
The next step
A shave is sized from interval data, not from a quote.
The review marks which peaks set the bill, tests power and energy combinations against the worst of them, and prices the held reduction on the assigned tariff. The inputs that make it quick:
- 01Twelve months of interval data, imports and exports, at the billing resolution
- 02Every billed maximum from the bills, with the date and interval it was set in
- 03The assigned tariff’s demand window, reset rules and kVA or kW basis
- 04Existing solar production, to judge recharge between peak days
- 05Planned new load—a site adding equipment grows into peaks the old data cannot show
Delivered example: All Secure, Three Kings — a 60 kWh commercial battery working alongside a 75.4 kWp rooftop array at a mixed-use facility.
Start with the controllable signal
Check the peaks and the tariff before choosing equipment.
Research and scheme sources
General information only. Market prices, retailer contracts, tariffs and scheme rules change. A project model requires current site data and current commercial terms.