Demand Charges and Solar for Australian Business

In short: demand charges bill your peak power draw (kW), not total energy (kWh), and they can be 30–50% of a commercial bill. Solar only cuts them when your peak falls during midday solar hours. On the worked example below, a 100 kW system paired with a battery pulls a 250 kW peak down by 50 kW and saves $10,800 a year on the demand line alone. If your peak is late afternoon or on cloudy days, solar by itself barely helps. Check your own load profile before assuming.

Demand charges can account for 30–50% of a commercial electricity bill in Australia. They are the single largest line item many businesses overlook when evaluating solar, because the assumption is straightforward: install solar, reduce consumption, save money. That logic holds for energy charges measured in kilowatt-hours. It does not automatically hold for demand charges measured in kilowatts.

Many businesses install solar expecting their entire bill to drop proportionally, then discover that the demand charge component barely moved. Understanding why this happens, and what strategies actually work to reduce demand charges, is critical to modelling accurate solar savings and avoiding a payback calculation built on incorrect assumptions.

What Are Demand Charges?

Demand charges measure your peak power draw in kilowatts (kW), not your total energy consumption in kilowatt-hours (kWh). Your electricity meter records the average power draw over every 15 or 30-minute interval throughout the billing period. The single highest interval becomes your demand reading for that month, and you are charged based on that peak.

Think of it this way: energy charges measure how much water you used over the month. Demand charges measure the widest you ever opened the tap. The electricity network must build and maintain infrastructure capable of servicing your highest instantaneous demand, and demand charges recover that infrastructure cost.

Typical demand rates for commercial customers in Australia sit between $10 and $25 per kW per month. A business with a peak demand of 80 kW pays between $800 and $2,000 per month in demand charges alone, before a single kilowatt-hour of energy is counted. For a site with a 120 kW peak, that figure can exceed $3,000 per month.

The charge is set by your worst moment. One hot Friday afternoon when every air conditioning unit, compressor, and piece of equipment runs simultaneously for 15 minutes can set your demand charge for the entire month. The other 43,000+ intervals in the billing period are irrelevant. Your bill reflects that single peak.

Worked Example: What 50 kW Off The Peak Is Worth

Take a manufacturing site drawing a 250 kW peak on a demand tariff of $18/kW/month, which sits mid-range for Australian commercial customers. Before any solar is installed, the demand component alone costs:

250 kW × $18/kW/month × 12 months = $54,000 per year

The site installs a 100 kW solar system. At midday in clear weather the array covers a large share of the load, but the demand charge is set by the worst interval of the month, not the average one. Overcast afternoons and the late-day production tail mean only part of the reduction is firm. A realistic firm reduction from solar alone on this load shape is about 30 kW. Adding a battery sized to discharge through the peak window lifts the firm reduction to 50 kW.

The battery is responsible for the difference between those two rows: an extra 20 kW of firm reduction worth $4,320 per year on the demand line. At an installed cost of $95,000 after the federal battery discount, the demand-charge saving alone repays the battery in 22.0 years, before counting the energy arbitrage and self-consumption value that arrive on top.

Together the two measures remove 20% of the billed peak and $900 a month. If this site is billed per kVA rather than per kW, the same 50 kW reduction at a 0.9 power factor is worth 55.6 kVA, so the saving is larger again on a kVA tariff.

Figures are illustrative and calculated live from the stated assumptions. Your firm reduction depends on when your peaks actually occur, which is a question your interval data answers and a rule of thumb does not.

What A Demand Reduction Is Worth At Other Rates

The saving scales linearly with both the demand rate and the kilowatts removed, so the same reduction is worth very different money depending on your tariff. Annual saving on a 250 kW peak:

Read your own demand rate off your bill before using any of these numbers. It is usually shown as a $/kW or $/kVA figure next to a "demand" or "capacity" line, and it is the multiplier that decides whether peak shaving is worth capital or not. Our bill guide shows where to find it.

Why Solar Alone Does Not Always Reduce Demand Charges

Solar generation follows the sun. Output ramps from zero at sunrise, peaks around midday, and declines through the afternoon to zero at sunset. For businesses whose peak demand occurs between 10 am and 2 pm, solar generation is at its strongest during the demand peak, and the reduction can be meaningful.

But many commercial demand peaks occur in the late afternoon, between 4 pm and 7 pm, when solar output is already declining or gone. Air conditioning load spikes during heat events that push grid demand to its highest, but those same heat events often occur in the late afternoon when ambient temperatures peak. Your HVAC system is working hardest precisely when your solar panels are producing least.

Cloud cover introduces another layer of unpredictability. Demand charges are set by the worst single interval. Even if solar covers your demand peak on 29 sunny days, one overcast afternoon where cloud cover drops your solar output to near zero while your equipment runs at full capacity is enough to set the demand charge for the entire month. Solar reduces average consumption reliably. It does not reduce worst-case peaks reliably, because you cannot guarantee clear skies during your highest-demand moments.

This is the gap that catches people out: energy charges are about averages, demand charges are about peaks. Solar is excellent at reducing averages and unreliable at eliminating peaks. It is also why the worked example above credits solar with 30 kW of firm reduction rather than the 100 kW nameplate: only the part of the output you can count on during the worst interval of the month reduces the bill.

Strategy 1: Battery Storage For Demand Shaving

Batteries address the core limitation of solar for demand management. A battery system stores excess solar energy generated during the middle of the day and discharges it during demand peaks, reducing the kW reading that sets your demand charge. The key specification is 15-minute discharge capability: the battery must be able to sustain its rated output for the full measurement interval, not just deliver a short burst.

Size both ratings against the peak you are shaving. The kW rating has to cover the reduction itself, so pulling a 250 kW peak back to 200 kW needs at least 50 kW of discharge power. The kWh rating has to hold that output for as long as the peak lasts, so a two-hour afternoon peak at 50 kW needs roughly 100 kWh of usable capacity set aside for demand duty.

Demand shaving starts to justify a battery once demand charges pass roughly $15/kW/month. At that rate, shaving 20–30 kW is worth $3,600–$5,400 a year. Be careful how you read that number: it is a contribution, not a payback. As the worked example above shows, demand savings on their own rarely repay a commercial battery inside a decade, because the saving is counted in thousands per year while the battery costs tens of thousands. Storage pays back on the stack of value together, with demand reduction sitting alongside energy arbitrage (charging off-peak, discharging during peak tariff periods), higher solar self-consumption, and backup power. Any quote that repays a battery on the demand line alone is either assuming a very large peak reduction or a very cheap battery, so check which. See the commercial battery storage guide for sizing and incentive detail.

Strategy 2: Load Shifting To Solar Hours

The cheapest demand management strategy costs nothing beyond programming time. Load shifting moves heavy electricity-consuming activities into solar generation hours, reducing both energy charges and the likelihood of demand peaks outside solar hours:

• HVAC pre-cooling: Run air conditioning at full capacity during morning solar hours (9–11 am) to cool the building mass, then reduce HVAC output during the afternoon peak tariff period.
• EV and forklift charging: Schedule electric vehicle and forklift fleet charging for 10 am–2 pm when solar output is highest.
• Water heating: Switch to heat pump or resistive hot water during solar hours instead of overnight off-peak.
• Equipment scheduling: Stagger start-up of heavy machinery to avoid simultaneous peak draws. A 5-minute delay between starting compressors can reduce your 15-minute demand reading significantly.

Load shifting is free to implement if your building management system or equipment controllers support scheduling. The impact on demand charges depends on how much of your peak you can move, but even a modest 10–15 kW shift is worth $2,160–$3,240 a year at the $18/kW/month rate used above, for no capital at all.

Strategy 3: Demand Response Programs

Demand response programs pay businesses to reduce their consumption during grid-wide peak events. When the electricity network is under stress (typically extreme heat days), the network operator or your retailer can call a demand response event, asking participating businesses to curtail non-essential loads for a defined period.

Payments vary by program and network area but typically range from $500 to $2,000 per event for commercial-scale participants. Some programs offer capacity payments (a monthly fee for being available) plus energy payments (per-event compensation). Available through AEMO's wholesale demand response mechanism and several retailer-specific programs, demand response turns your ability to reduce consumption into a revenue stream.

Strategy 4: Time-Of-Use Tariff Optimisation

Not all tariff structures treat demand the same way. Some commercial tariffs have demand charges that apply only during peak periods. Others measure demand across all hours. Some use a ratchet mechanism where your demand charge is based on the highest peak in the last 12 months, not just the current billing period.

The ratchet is worth pricing separately, because it changes what a single bad interval costs. On the reference site, one uncontrolled 250 kW spike sets $54,000 of demand charges for the following twelve months even if the site never draws that much again. Under a non-ratcheted monthly tariff the same spike costs $4,500 and then clears.

Reviewing your tariff structure with solar in mind can reveal opportunities. A business on a flat-rate tariff with embedded demand costs might benefit from switching to a time-of-use tariff where solar directly offsets the most expensive consumption periods. Conversely, a business on a demand-heavy tariff whose peak occurs outside solar hours might save more by switching to a tariff with higher energy rates but lower or no demand charges. Your retailer's network tariff assignment determines which structures are available. Our TOU tariff guide covers how the windows interact with solar.

When Solar Does Reduce Demand Charges

The preceding sections might suggest solar never helps with demand, but that is not the case. Solar directly reduces demand charges when your peak demand aligns with peak solar generation. This is common in several business types:

• Warehouses with day-shift operations: Peak demand during loading, forklift activity, and daytime lighting falls squarely in the 10 am–2 pm solar window.
• Offices with 9–5 schedules: HVAC and lighting loads peak during business hours. If your building is well-insulated and the afternoon ramp-down is gradual, solar covers the demand peak.
• Schools and education facilities: Operating hours and peak loads align closely with solar generation. Weekend and holiday periods mean low demand and high export, but demand charges are set by the school-day peaks.

The critical step is checking your load profile before making assumptions. Request interval meter data from your retailer (most smart meters record 15-minute or 30-minute intervals) and identify when your demand peaks actually occur. If your top 10 demand peaks all fall between 10 am and 2 pm, solar will reduce your demand charges. If they cluster after 4 pm, solar alone will not, and you need one of the strategies above.

Model Your Demand Charges Accurately

Demand charges are too significant to estimate. A $15/kW/month rate on an 80 kW peak adds $14,400 per year to your electricity cost, and the reference site above carries $54,000 a year on the demand line before a kilowatt-hour is billed. Whether solar, batteries, load shifting, or tariff restructuring reduces that figure depends entirely on your specific load profile and tariff structure.

Start by understanding your current bill. Then model how solar generation interacts with your actual consumption patterns, not just your annual total.

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