Peak Shaving Calculator
Demand charge calculator for commercial peak shaving: estimate shaved kW savings, battery inverter kW, rated kWh, EV fleet charging peaks, demand-ratchet limits, and simple payback from manual inputs or interval data.
Reviewed June 2, 2026. JouleIO calculators are planning tools; confirm final utility rates, equipment specs, incentives, installation bids, and safety decisions with official utility, manufacturer, installer, DOE, ENERGY STAR, EPA, IRS, or EIA sources.
1. Enter real usage
Use your actual watts, runtime, home size, miles, battery size, or appliance schedule.
2. Localize the rate
Compare national assumptions with your state, utility bill, time-of-use plan, or project quote.
3. Verify before acting
Check final prices, rebates, tax rules, and safety requirements before buying or installing equipment.
Commercial demand charge calculator
Calculate shaved kW savings, battery power, battery kWh, and demand-ratchet limits
Peak shaving only works when the shaved kW repeats often enough to pay for storage and the utility tariff actually credits the lower peak. Use the presets below to see how warehouse HVAC peaks, EV fleet charging, grocery refrigeration, interval data, and demand ratchets change the battery kW, battery kWh, and payback math.
Fast answer
Peak shaving reduces the highest billed kW interval, not total monthly kWh. Demand-charge savings are shaved kW times the $/kW-month tariff.
Battery size
For manual sizing, use shaved kW times peak hours, then adjust for depth of discharge and round-trip efficiency.
Better method
With interval data, sum only the kWh above the target demand threshold because real peaks are rarely flat rectangles.
Demand charge triage
Before buying storage, identify what is creating the peak
The cheapest peak-shaving project is often not a battery first. Use interval data to find whether the billed peak comes from EV charging, HVAC startup, refrigeration, compressed air, or a one-time operational spike. Then compare controls, scheduling, and storage in that order.
EV charging depot
Typical trigger: Many Level 2 or DC chargers start in the same evening window.
First move: Test managed charging, lower charger power, and staggered start times before sizing storage.
Grocery or cold storage
Typical trigger: Refrigeration compressors, HVAC, lighting, and defrost cycles overlap.
First move: Protect refrigeration reliability first, then model how much kW can be shaved safely.
Warehouse or light industrial
Typical trigger: Rooftop HVAC, compressors, conveyors, and shift startup happen together.
First move: Sequence equipment and controls before assuming a battery is the cheapest fix.
School, church, or community facility
Typical trigger: Short event peaks from HVAC recovery, kitchens, lighting, and occupancy.
First move: Check how often the event repeats in billed months; one rare spike may not justify storage.
Bill component map
Demand charge savings are kW savings, not ordinary kWh savings
Many weak peak-shaving estimates mix demand charges and energy charges. This calculator keeps them separate so the result can be checked against a real commercial utility bill.
| Component | Bill unit | What changes it | Use here |
|---|---|---|---|
| Demand charge | $/kW-month | Lowering the single billed peak kW, or the on-peak period kW if the tariff only bills a window. | Enter current peak kW, target shaved kW, demand rate, and any ratchet floor. |
| Energy charge | $/kWh | Using fewer total kWh or shifting kWh into lower-priced hours. | Use the time-of-use calculator for energy shifting; this page focuses on kW demand. |
| Battery power | kW | How much load the battery inverter can cover at once. | Target peak reduction is the first-pass inverter kW requirement. |
| Battery energy | kWh | How long the battery can sustain the shaved kW. | Use interval data when possible; it is more realistic than one flat peak-hour assumption. |
Used when no interval data is pasted. Find this on the demand line of a commercial utility bill.
How much peak load the battery should shave.
Commercial tariffs often charge $10-$30 per kW-month.
How long the battery must discharge to cover the peak.
Use a quote if available; otherwise start with $500-$900/kWh.
Optional. Use 0 if your tariff has no demand ratchet or look-back billing peak.
Optional. Example: 80 means billed demand cannot fall below 80% of the prior peak.
Interval Demand Analyzer
Paste 15-minute, 30-minute, or hourly kW readings from a utility bill export. The calculator will size the battery from the real demand above your target peak.
Readings
0
Observed Peak
0 kW
95th Percentile
0 kW
Average Load
0 kW
Monthly Savings
20 billable kW saved
Battery Size
40 usable kWh needed
Simple Payback
$4,320/yr savings
Billable Peak
Ratchet floor 0 kW
Battery Power
20 kW
First-pass inverter discharge rating.
Rated Duration
2.5 hr
Rated kWh divided by shaved kW.
Demand Bill Cut
20%
$1,800 to $1,440 before other bill lines.
Decision Signal
Possible case; verify controls and tariff
2 hour manual peak window
Peak Shaving Result
Shaving 20 kW from a 100 kW monthly peak lowers the physical peak to 80 kW, a 20% reduction. After the optional demand-ratchet floor, the modeled billable demand changes from 100 kW to 80 kW. At $18/kW-month, that saves about $360 per month before battery degradation, controls, maintenance, financing, taxes, and utility tariff details.
The battery needs about 40 usable kWh to hold the shaved load for 2 hours. After depth of discharge and round-trip efficiency, the rated battery size is about 49.4 kWh. At $650/kWh, the modeled installed cost is $32,099.
The inverter must be able to discharge about 20 kW during the peak. If the target peak lasts longer than expected, the bottleneck becomes battery kWh. If the spike is very short and tall, the bottleneck is usually inverter kW and controller response.
Citable calculator answer
How to calculate demand charge savings
Monthly demand-charge savings equal shaved billable kW x $/kW-month. A 100 kW reduction on a $20/kW-month tariff saves about $2,000 per month before ratchets, standby charges, battery losses, controls, financing, and maintenance. First-pass battery sizing is shaved kW x peak hours / depth of discharge / round-trip efficiency. With 15-minute interval data, sum only the kWh above the target demand threshold.
Step 1
Find billed kW, demand rate, and ratchet language on the tariff.
Step 2
Set the target kW threshold and calculate kWh above that line.
Step 3
Compare storage against controls, managed charging, and TOU shifting.
Peak Shaving Formula
Monthly savings = shaved kW x demand charge
Billable demand = max(current month peak, prior look-back peak x ratchet %)
Battery kWh = shaved kW x peak hours / (DoD x efficiency)
Interval battery kWh = sum(max(0, interval kW - target kW) x interval hours) / (DoD x efficiency)
Simple payback = installed battery cost / annual demand savings
Which Method Should You Use?
Quick quote screen
Use current billed peak, target kW reduction, and peak duration when you only have a bill or battery quote.
Interval-data sizing
Paste 15-minute or hourly kW readings when the decision depends on the actual shape of the peak.
EV charger triage
If EV chargers create the spike, first test managed charging, lower amperage, and staggered start times.
Demand Charge Data Notes
Peak shaving is sensitive to tariff rules, demand ratchets, and the interval used by the utility. NREL notes that many demand charges are set from the highest average usage in a defined interval, often 15 minutes, and that storage can reduce those charges by discharging during facility peaks. For EV depots, also test managed charging because staggered start times can reduce peak kW without buying as much battery capacity.
Billed demand kW
Use the maximum demand or billing demand line from the latest commercial electric bill.
$/kW demand rate
Use the demand charge line item, not the energy $/kWh rate.
Interval export
15-minute or hourly kW data makes storage sizing more realistic than one peak-duration guess.
Demand ratchet
If the tariff bills a percentage of a prior peak, include the look-back peak before estimating savings.
When Peak Shaving Works Best
- High demand charges: The higher the $/kW-month charge, the more valuable each shaved kW becomes.
- Predictable peaks: Batteries work best when peaks occur at known times, such as EV charging, HVAC startup, manufacturing shifts, or refrigerated load cycles.
- Short peak windows: A 20 kW peak that lasts 1 hour needs far less battery than a 20 kW peak that lasts 5 hours.
- No cheaper control fix: If sequencing compressors, HVAC, or EV chargers removes the same peak, do that before buying storage.
- Stacked value: Payback improves if the battery also supports backup power, time-of-use arbitrage, solar self-consumption, or resilience.
Best-Fit Commercial Loads
EV fleet depot
Chargers start in the same evening window and create a repeated kW spike.
First check
Compare managed charging against battery shaving before buying storage.
Warehouse HVAC
Rooftop units and loading operations overlap during hot afternoons.
First check
Use interval data to see whether the peak is one short startup or a multi-hour plateau.
Grocery refrigeration
Compressors, cases, HVAC, and defrost cycles stack into recurring peaks.
First check
Confirm the target kW reduction will not compromise refrigeration reliability.
Light manufacturing
Shift startup, compressed air, motors, and process equipment create billing peaks.
First check
Audit sequencing and controls before sizing a battery.
Next Step
Use this calculator for a first-pass estimate, then compare it with your utility tariff and interval meter data. If the same peak happens only once per year, economics may be weak. If the peak repeats every billing cycle, a battery controller can often target it more reliably. For storage sizing beyond demand charges, compare this with the Solar Battery Calculator.
Frequently Asked Questions
What is peak shaving?
Peak shaving reduces the highest short-duration power draw on an electric bill. A battery discharges during the peak window so the building sets a lower billed demand peak in kW, which can reduce monthly demand charges.
How do I size a battery for peak shaving?
With a simple estimate, multiply target kW reduction by peak hours, then adjust for battery depth of discharge and efficiency. With interval meter data, sum only the kWh above the target demand threshold. That is usually more accurate than one peak-hour assumption.
Is a demand charge the same as an energy charge?
No. A demand charge is billed on the highest kW peak in a billing period or demand window, while an energy charge is billed on total kWh used. Peak shaving targets demand charges; time-of-use shifting targets energy charges.
When does peak shaving pay back?
Peak shaving tends to pay back when demand charges are high, peaks are predictable, and the battery can be used many months per year. Low demand charges, short billing windows, or unpredictable peaks can make payback weak.
What is a demand ratchet?
A demand ratchet is a tariff rule that can bill a facility on a percentage of a previous peak instead of only the current month peak. If the ratchet floor is higher than the post-storage peak, the battery may reduce physical kW but not the billed demand charge by the same amount.
Can EV charging create a demand charge problem?
Yes. A small number of Level 2 chargers or one DC fast charger can create a new monthly kW peak if vehicles charge at the same time. Before buying a battery, compare managed charging, lower charger power, staggered start times, and time-of-use windows against storage.