Ask most South African business owners what they pay for electricity and they'll quote you a monthly rand figure. Ask how that figure breaks down, and things get less clear. Ask specifically about their demand charge — and most have never heard the term.
That's a problem, because for many commercial and industrial accounts, the demand charge is not a minor line item. It can account for 30–50% of the total electricity bill.
What Is a Demand Charge?
A demand charge is a fee based not on how much electricity you use, but on how fast you use it — your peak rate of consumption during a billing period, measured in kilovolt-amperes (kVA).
Here's how it works: your municipality's billing system monitors your electricity consumption continuously. At the end of each month, it identifies the single 30-minute window in which your demand was highest. That peak reading, measured in kVA, becomes your "recorded maximum demand" for the month — and your demand charge is calculated against it.
The logic is straightforward from the municipality's perspective: they need to build enough grid capacity to serve your business at its maximum possible draw, not just its average draw. The demand charge funds that capacity.
Why This Matters for Your Bill
Demand charges work on a peak principle. Even if your maximum demand occurred in a single 30-minute window due to an unusual event — a large motor starting up, HVAC systems cycling on simultaneously, production equipment coming online after load shedding — you pay for that peak across the entire month.
This means that managing your peak demand — spreading large loads, staggering equipment start-up sequences, avoiding simultaneous activation of high-draw systems — can reduce your electricity costs significantly without reducing a single unit of consumption.
When Demand Charges Become Billing Errors
Demand charges are legitimately complex. But they become billing errors when:
- Your CT ratio is wrong. Larger commercial accounts use current transformers (CTs) to scale meter readings. The CT ratio — the factor by which actual current is divided before metering — must be correctly recorded in the billing system. A CT ratio error multiplies every reading, including your demand reading, by the wrong factor. A factor-of-2 error doubles your recorded demand and your demand charge simultaneously.
- Your tariff category includes a demand charge it shouldn't. If your account is billed under a tariff category designed for large commercial customers — and you're not one — you may be paying a demand charge that doesn't apply to your correct tariff structure.
- Estimated demand readings are applied incorrectly. In some billing system configurations, demand readings can be estimated when actual meter data isn't captured. Estimated demand figures are frequently higher than actual — and rarely corrected retrospectively.
Standard vs. Time-of-Use Demand Charges
Not all tariff structures apply demand charges the same way. Under a standard tariff, your demand charge is based on your peak kVA recorded at any point during the month, regardless of when it occurs. Under a time-of-use (TOU) tariff, demand is typically measured during designated peak periods — meaning your off-peak demand may not contribute to your maximum demand charge at all.
If your business operates heavy loads primarily during standard or off-peak periods, a TOU tariff may reduce your effective demand charge significantly. Conversely, if you're on a standard tariff and your peak demand consistently occurs during off-peak hours, you're paying full demand rates for demand that would be discounted under a TOU structure.
Tariff optimisation — reviewing whether your current tariff structure suits your actual consumption profile — is frequently the highest-value intervention an electricity review can deliver.
What to Check on Your Invoice
Your electricity invoice should show a separate demand or "maximum demand" line item, with your recorded kVA figure and the applicable rand-per-kVA rate. If you see a demand charge but the kVA figure looks disproportionately high relative to your operational footprint, that's worth investigating.
Compare your recorded demand kVA across the last 12 months. A spike that doesn't correspond to any change in your operations — no new equipment, no production increases — could indicate a meter error, a CT ratio mismatch, or a data capture problem in the billing system.
Demand Charge Errors Are Recoverable
Billing errors that result in inflated demand charges can be disputed and recovered. Municipalities are required to correct accounts when meter data or tariff applications are proven to be wrong, and credits can be applied retroactively — often for up to three years of affected billing.
The first step is knowing whether your demand charge is accurate. If you've never verified it against your meter configuration and tariff category, you're operating on assumption.
Check Your Rate Now
The OptiRate Rate Calculator helps you assess whether your current electricity billing — including any demand charge component — aligns with your consumption profile and the applicable tariff structure for your area.