Why WA homes don't pay peak demand charges

What a demand charge is

A demand charge bills a customer for the highest rate of draw they reach in a period, measured in kilowatts, rather than for the total energy they use. A short burst of heavy load can set the charge for a whole month. Because it rewards flattening peaks, a battery that discharges during those bursts can pay for itself quickly on a tariff that has one.

Why Synergy residential plans don't have one

Demand charges are a business-tariff concept. Synergy's residential plans, including the flat Home Plan and the Midday Saver time-of-use plan, bill a fixed daily supply charge plus energy consumed in cents per kilowatt-hour. There is no kilowatt-based demand component on a household bill, so there is no demand charge for a home battery to shave. A calculator built around one produces a saving that never shows up.

What drives a Perth battery's value instead

• Self-consumption. Every kilowatt-hour of stored solar you use in the evening replaces grid energy bought at the retail rate. This is the largest lever for most households.
• Export timing. Under DEBS, exports in the evening peak window are credited at a higher rate than daytime exports, so a battery that shifts exports into that window earns more. Model it with the DEBS calculator.
• Time-of-use arbitrage. On Midday Saver, charging from cheap daytime energy and discharging through the peak period widens the gap the battery captures.
• Payback. Put the pieces together, including the WA battery rebate, with the ROI calculator.