The demand charge is the line item a behind-the-meter battery can defend

The line item many businesses do not understand

A commercial electricity bill normally combines an energy charge, fixed charges and a demand charge. The energy component measures how much electricity the site uses over time. The demand component measures how fast it uses electricity at its highest point.

Two facilities can consume very different monthly energy and still face the same demand charge if they reach the same peak. A compressor, chiller, crusher or cluster of EV fast chargers can set that peak in a single interval, leaving the customer paying for capacity that was needed only briefly.

How peak shaving works

A battery behind the main meter monitors site load and defends a target demand ceiling. When load begins to exceed that ceiling, the battery discharges and clips the peak seen by the network. It recharges when load and tariff conditions allow.

The control problem is harder than the diagram. The system must decide how much state of charge to preserve, which peak is likely to matter and whether a later event will be higher. One missed peak can reset the billing maximum and erase much of the month’s expected saving.

Value stacking — useful, but only when it is real

The same battery may support several value streams:

• Peak-demand shaving against a kW or kVA network charge.
• Tariff optimisation, including staying below a threshold that changes the applicable tariff.
• Energy arbitrage between low- and high-price periods.
• Demand response, FCAS or network support, where market access and operating constraints permit.
• Solar self-consumption by shifting surplus generation into a later load period.

Stacking does not mean adding every spreadsheet benefit. Each service competes for power, energy capacity and state of charge. The defensible case is the compatible stack the control system can actually deliver under the customer’s tariff and operating profile.

The Australian translation

Australian commercial and industrial tariffs commonly recover part of network cost through measured peak kW or kVA, sometimes within defined time windows and sometimes with ratchet effects. That makes the local opportunity highly site- and tariff-specific.

For depots, logistics facilities, mine workshops and industrial sites electrifying fleets or adding large intermittent loads, the demand component can become more important even when annual energy use looks manageable. The first feasibility task is therefore not choosing a battery. It is reconstructing the delivered-cost stack from bills, interval data and the applicable network tariff.

The traps that belong in the model

• Size to the shape and volatility of the load. Nameplate peak alone does not reveal how long the event lasts or how predictable it is.
• Derate forecast savings. Volatile loads, solar variability, outages and changing operating schedules reduce perfect-model performance.
• Check tariff rules. Billing windows, kVA measurement, ratchets and threshold changes can matter more than the nominal demand rate.
• Separate resilience. A battery sized to clip short peaks is not automatically capable of carrying critical load through an outage.
• Test degradation and availability. The valuable peak may occur when the battery is unavailable, energy-limited or preserving warranty constraints.

Commercial structure matters

The customer does not always need to fund the asset directly. Shared-savings agreements, fixed service payments, solar-plus-storage PPAs and performance contracts can convert an uncertain capital decision into an operating-cost proposition. But the contract must say who carries performance risk when the peak is missed, the tariff changes or the operating profile moves.

The Pre-DD takeaway