Commercial Demand Charge Calculator for Battery Peak Shaving
For commercial and industrial facilities. Enter your monthly peak, tariff rate and battery size to see the kW it can clip and the demand-charge dollars that frees up.
How to Calculate Commercial Demand Charges
Commercial electricity bills usually carry two parts: energy (kWh consumed) and demand (the highest sustained kW in the billing period). Demand charge equals the billed peak kW multiplied by the tariff rate in $/kW. Depending on the utility, that peak may be a 15- or 30-minute interval rather than an instantaneous spike.
How Battery Peak Shaving Savings Are Calculated
A battery discharges during the site peak so the meter sees less demand. This calculator uses the lowest of the site peak, battery power and the kW the usable energy can sustain for the full peak window; it then multiplies that shaved kW by the demand-charge rate.
Peak shaving is the fastest-paying layer for most C&I batteries. For how it fits alongside other value streams, read the peak shaving explainer.
Battery Power vs Usable Energy Limits
Battery power determines how much of a peak can be clipped at one moment. Usable energy determines how long that output can last. A 215 kW battery with 430 kWh usable energy can support 215 kW for two hours; a longer demand window lowers the sustained shave unless the system has more usable energy.
- Power-limited shave
- When battery kW is below the site peak, the inverter or battery power rating caps the reduction, even if the battery has plenty of usable energy.
- Energy-limited shave
- When usable kWh cannot hold the requested battery kW for the full demand window, sustained shave is capped at usable kWh divided by window hours.
- Peak-window check
- Enter the demand interval from the tariff or load data. The calculator preserves both the power limit and energy limit instead of treating peak shaving as a simple rate multiplication.
- Commercial sizing signal
- Use the output as a first sizing screen before a dispatch and tariff review. The system still needs to cover the actual load shape, availability and operating constraints.
Demand Charge Savings Example
With a 500 kW monthly peak, a $20/kW/month demand charge, 215 kW of battery power and 430 kWh usable energy, the battery can shave 215 kW for a two-hour window. That is $4,300 per month or $51,600 per year before other BESS value streams are considered.
| Demand-charge rate | Typical commercial tariff context |
|---|---|
| $10/kW/mo | Low C&I / smaller utilities |
| $15/kW/mo | Typical secondary-voltage C&I |
| $20/kW/mo | Mainstream US commercial tariff |
| $25/kW/mo | High-demand-charge territory (e.g. parts of CA, NY) |
Rates vary widely by utility and tariff. Read the demand-charge line off an actual bill before trusting a number — the presets above are a US C&I starting range, not a quote.
Assumptions and Limitations
- One revenue layer
- Demand-charge reduction only. No energy arbitrage, capacity, frequency revenue, ITC or other tax credits — so this is not a payback or full-ROI number.
- Reliable clipping
- The battery is available and clips the peak every billing period. A single missed month resets that month's charge to the un-shaved peak.
- One sustained window
- The peak is treated as a single block of the duration you enter. Real load shapes with several separate peaks may need more energy to cover all of them.
- Estimate, not a tariff quote
- Confirm the demand interval, ratchet clauses, seasonal rates, site controls and actual billing demand with the tariff and interval data before buying equipment.
FAQ
What is a demand charge?
A demand charge bills C&I customers on their highest sustained kW draw in the month, separate from the kWh they use. A single spike can set the charge for the whole billing period.
How do you calculate a demand charge on an electricity bill?
For a billing month, multiply the highest metered demand in kW, often the highest 15- or 30-minute interval, by the tariff demand-charge rate in $/kW. When a battery clips the peak, subtract the shaved kW before applying that rate.
How does a battery cut a demand charge?
The battery discharges during the site peak, so the meter sees a lower net kW. The reduction in peak kW multiplied by the demand rate is the monthly saving.
Why does my battery only shave part of the peak?
Two limits apply. Power-limited: the battery kW is below the peak kW. Energy-limited: usable kWh is too small to hold that power for the whole peak window, so the sustained shave drops to usable kWh / window hours.
What does this calculator NOT include?
It models demand-charge reduction only. It excludes energy arbitrage, capacity or frequency revenue, the ITC and other tax credits, degradation, efficiency losses and CAPEX, so it is not a payback or full-ROI figure.
Need the battery behind the savings?
Hua Power builds the LFP cabinets and containers that shave C&I peaks. Tell us your peak kW and window and we will spec a system sized to actually hold it.