Demand Charges Explained - Why One Hot Afternoon Can Set Your Business's Power Bill

Two Melbourne businesses can use the same number of kilowatt-hours in a month and get wildly different power bills. The difference is usually one line most owners have never been shown how to read: the demand charge. On many commercial tariffs you aren't just billed for the energy you use - you're billed for the fastest you ever used it, measured in kilowatts over short intervals, typically half an hour. Your single hungriest half-hour can set a charge that has nothing to do with how frugal the other 1,400-odd half-hours of the month were. Most owners discover this line the month after their first proper heatwave, which is why we're writing about it in October.

What a demand charge actually is

Networks size poles, wires and transformers for the worst moment, not the average one - so commercial tariffs charge for your contribution to that worst moment. Your meter records consumption in intervals, and the demand charge keys off the highest interval in the billing period: run everything at once for half an hour and you've set your peak, even if the site idles the rest of the month. On some tariffs it's measured in kVA rather than kW, which also drags power quality into the bill, and depending on the tariff a single high reading can echo through more than one billing period. The exact mechanics vary by retailer and network - which is why the first step is always reading your actual tariff, not a generic article, ours included.

Why summer writes the number

For most Melbourne sites the year's peak lands on a hot afternoon between December and February: cooling flat out, refrigeration working hardest, every machine and screen on, all between roughly 2pm and 6pm. One 38-degree Thursday can set the month's demand line. That's also what makes demand charges attackable - they're concentrated in a few predictable hours, and anything that trims those specific hours punches far above its weight on the bill.

Reading your own bill

• →Find the line billed in kW or kVA rather than kWh - names vary: demand, capacity, peak demand
• →Ask your retailer for your interval data, or let us pull it with your authority - it shows exactly when your peaks happen and what they cost you
• →Answer three questions: how high is the peak, what time does it land, and what's actually running in that half-hour - every lever below starts from those answers

The levers that actually move it

Scheduling is the free one: hot water, pumps, plant and fleet or staff EV charging that currently stack onto the afternoon peak can often shift to mornings or overnight with timers and load management, shaving the peak without changing what the site does. Solar is the structural one - a commercial array generates hardest in exactly the hours summer demand charges bite, which is why we size systems from your interval data for self-consumption and peak reduction rather than from a roof measurement alone. Batteries are the precision tool: a commercial battery that discharges through the critical afternoon window caps the peak the meter ever sees, which is the peak-demand shaving we design battery storage systems around. And on kVA-billed sites, power factor correction is sometimes the cheapest kilovolt-amp you'll ever claw back - a conversation worth having before any of the bigger spends.

Owners corporations, this is your bill too

Common property is a commercial site: lifts, carpark lighting and ventilation, pool plant, and increasingly the shared EV charging we covered in apartment ev charging melbourne owners corporations all meet a commercial tariff with a demand component. The same sequence applies - interval data first, scheduling and load management second, commercial solar and storage where the numbers support them - and the benefit lands on every lot's levies. It pairs naturally with the capacity assessment a building does before adding chargers, because both start from the same data.

Demand charges reward the sites that understand them and quietly tax the ones that don't. If yours has never been looked at, October - before the first heatwave writes this summer's number - is the right month. Our commercial team works across metropolitan Melbourne: licensed A-Grade electricians, REC 37142, SWMS and inductions handled, fixed-price quotes typically returned within 2 business hours.