Demand charges in Perth: the line item on every commercial bill

A commercial energy bill in Perth tells you almost nothing about why it costs what it costs. There's a total dollar figure, a few line items, maybe a graph that shows last month next to this month. Most operators check the total, file the bill, and move on.

Hidden inside that total is a line called the demand charge. On most WA commercial sites, it's the single biggest cost on the bill. Bigger than the energy consumed. Bigger than the connection fees. Bigger than the capacity contribution.

It's also the line most actively manageable, the line most poorly understood, and the line moving fastest under the network tariff restructure already in progress in WA.

This piece walks through how demand charges work on a Perth commercial bill, why they dominate the total, and what changes them.

What a demand charge actually is

Energy charges scale with how much electricity you use. A kilowatt-hour is a kilowatt-hour, billed at a rate per unit. Total it up at the end of the month, multiply by the rate, done.

Demand charges scale with how much electricity you needed available to you at a single moment, regardless of how long that moment lasted. Western Power and the network charge for the size of the connection your site demanded, not the volume that flowed through it.

The logic is structural. The wires, transformers, and substations that carry electricity to your site have to be sized for your peak. They have to handle the moment when you're drawing the most. The cost of that infrastructure is recovered through demand charges, calculated against your peak draw in defined windows.

A site that runs steady all day, with no sharp peaks, has a relatively small demand charge. A site that runs flat for most of the day but occasionally spikes hard, even briefly, has a relatively large demand charge.

The peak doesn't have to last long. A 30-minute window of high draw can set the demand charge for an entire month.

How it's calculated

Western Power calculates demand on commercial network tariffs against the site's highest 30-minute average draw within the relevant billing window. The exact rules vary by tariff class, but the principle is consistent: identify the worst window in the period, multiply that by the demand rate, charge it.

For most commercial sites in WA, the demand rate sits somewhere in the range of $10 to $40 per kVA per month, depending on the tariff class, the connection size, and the network area. The number of kVA charged is set by that one 30-minute window of highest draw.

Multiplied out, the maths is simple. A 100 kVA peak on a $25 per kVA per month tariff is $2,500 a month, or $30,000 a year. A 300 kVA peak on the same tariff is $7,500 a month, or $90,000 a year.

Most commercial operators have no real-time view of what their current month's peak is sitting at. They see it on the bill, retrospectively, weeks after the window that set it.

Why it dominates the bill

For most WA commercial sites with a connection above about 30 kVA, the demand charge represents 35 to 60 per cent of the network portion of the bill, and 25 to 45 per cent of the total bill including energy. On heavier industrial sites, it can be higher.

The reason is the structural shift the WA network has been undertaking for several years now. The Australian Energy Regulator and Western Power have been progressively rebalancing how commercial network costs are recovered, moving weight from per-kWh energy charges to per-kVA demand charges. The direction is consistent across each pricing cycle. See the network tariffs explainer for the running view.

The practical effect is that the demand charge has grown faster than the energy charge for most of the last decade. A site that didn't notice the demand line on its bill in 2015 finds it dominates the bill in 2026.

What sets a peak in Perth

The 30 minutes that sets a Perth commercial demand charge usually comes from a small number of recurring patterns.

HVAC ramps on hot days. Air conditioning across a commercial site comes on hard when external temperature climbs. A 38-degree Perth afternoon pulls the HVAC system to maximum at exactly the moment most other commercial sites in the city are doing the same. The peak window for HVAC-dominated sites is usually between 2pm and 5pm on the hottest days of summer.

Plant cycles in industrial sites. Manufacturing, food processing, cold storage, and similar industrial operations have specific plant that pulls heavy load when it cycles on. A compressor starting up, a freezer defrosting and recovering, a process line beginning a batch. If these events stack, even briefly, the peak is set.

Morning starts on commercial sites. Many commercial buildings see their peak in the first hour of operations. HVAC ramps from overnight setback to operating temperature, lighting comes on across the floor, kitchen and amenity loads kick in. The 8am to 9am window is a common peak-setter for office and retail sites.

EV charging events. As commercial sites add EV charging infrastructure, an unmanaged fleet plugging in at 5pm becomes a new peak-setter that didn't exist five years ago. Read more in EV charging optimisation.

Equipment failure or startup. A piece of equipment running outside its normal envelope, a backup system kicking in, a startup sequence after maintenance. Operational events that happen rarely but pull hard can set the entire month's demand charge.

In most cases, the operator doesn't know the peak window was a peak window until the bill arrives. By then it's locked in for that billing period.

Five ways the peak moves

The demand charge moves in response to a small number of structural levers.

Load shifting. Flexible loads that don't care exactly when they run get moved out of the peak window. Pre-cooling buildings before the hottest part of the day. Pre-charging cold rooms during overnight off-peak hours. Running pumps in the middle of the night rather than mid-afternoon. The total energy used stays the same. The peak shrinks. Read more in load management.

Load shedding. Non-critical loads get briefly stood down during a forecast peak event. The trade-off is operational impact versus dollars saved. On sites with a clear set of non-critical loads, this is a powerful lever. On sites where everything matters, less so.

Battery dispatch. A battery discharging during the forecast peak window directly reduces the kW drawn from the network during that window. The battery doesn't have to be large to make a difference, because the demand charge is set by the peak kW, not the cumulative energy. A 100 kW battery discharging for 30 minutes can shave a 100 kW demand peak. Read more in battery management.

Solar coordination. Solar generating during the peak window reduces the net draw from the network during that window. Solar is less reliable as a peak-shaving tool because the peak can occur in weather that affects generation (cloud cover, heat-induced derating), but it contributes when it's available.

Network tariff reclassification. Some sites are on the wrong network tariff for their consumption pattern. A site classified under a tariff with heavier demand weighting than necessary pays more than it should. Reclassification, where available, can move the bill without changing any operational behaviour. Read more in tariff broking.

The first four levers reduce the peak. The fifth changes how the peak is charged. All five are part of what active management works through.

What active management actually does

Active management of demand charges runs continuously. The platform forecasts the upcoming peak window every interval, against weather, time of day, day of week, recent load behaviour, and the rolling demand position for the current billing period.

When the forecast indicates a peak window is imminent, the platform takes action. Load shifts. Storage dispatches. Solar self-consumption is optimised. The site arrives at the peak window operating at a reduced kW level, and the demand peak is held below where it would otherwise have landed.

The work is invisible to the building. Lights stay on. HVAC maintains comfort. Production runs. The schedule of flexible loads changes in the background. The bill notices.

Across our modelling on typical Perth commercial sites, active management of demand charges reduces the line item by between 15 and 40 per cent on most sites with any flexibility. On sites with a battery, the reduction can be higher. On sites with no flexibility and no storage, the reduction is more modest but rarely zero.

Specific situations

A few specific site situations come up repeatedly in our work.

The site that hit a one-off peak. A site has a single 30-minute window in the year where it drew significantly above its normal operating envelope. The cause was a one-off event, often equipment startup or a backup system test. That single window sets a substantially higher demand charge for that month and, in some tariff classes, ratchets the demand baseline upward for an extended period. Active management can prevent these one-off events from setting the charge by detecting the ramp and intervening before the 30-minute window closes.

The site with consistent high peaks. A site has a consistently high peak driven by the way the building operates. HVAC, plant, or load patterns that genuinely require the peak load. The active management answer here is harder. Some peaks are real and unavoidable. Others appear unavoidable but turn out to have flexibility that wasn't visible from outside the platform's modelling.

The site with growing EV load. A site is adding EV charging without a clear plan for how that load interacts with the existing peak demand. Without coordination, the EVs become the new peak-setter and the demand charge rises materially. With coordination, the EVs charge in windows that avoid the peak and the demand charge stays close to where it was.

The site that hasn't reviewed its tariff in a decade. The site is on a network tariff classification chosen when the connection was first established. The consumption pattern has changed since. The right tariff class for today's operation isn't the one the site is on. The fix is administrative, not operational.

The numbers across typical Perth sites

The demand charge line on a typical Perth commercial site sits somewhere in the following ranges. These are illustrative. The actual number depends on the connection size, the tariff class, the consumption pattern, and the network area.

Small commercial site (light retail, small office, light industrial): Connection capacity around 50 to 150 kVA. Demand charge running roughly $5,000 to $30,000 per year. Material but not dominant on these sites; energy charges often the larger line.

Mid-size commercial or light industrial: Connection capacity 150 to 500 kVA. Demand charge running roughly $20,000 to $150,000 per year. Usually the largest single line on the bill.

Larger commercial or industrial: Connection capacity 500 kVA to 1.5 MVA. Demand charge running roughly $100,000 to $500,000 per year or higher. Dominates the bill and dominates the active management opportunity.

The active management saving on each of these scales is meaningful. The absolute dollars are larger on larger sites, but the proportional impact is similar across site sizes. On most sites, the demand charge line is the largest single addressable item under active management.

For any commercial operator looking at rising energy costs in WA, the demand line is the first place to look. Not because it's easy to move, but because it's the line where the dollars actually are.

Demand charges are the line item on a Perth commercial bill that responds most directly to active management. They're the largest single line on most commercial bills above light commercial scale. They're the line moving fastest under the WA network tariff restructure already in progress.

The honest position

We model demand exposure as part of every site review. The review is free. The output is a quantified view of what active management would change on your site, against the way your bill is actually structured.