Maximum Demand: Why One Bad Half-Hour Costs So Much

If you run or pay for a medium or large building in Malaysia — an office tower, a mall, a factory, a hospital — there is one line on your electricity bill that behaves unlike anything else you pay for. It is not based on how much electricity you used all month. It is based on your single worst 30 minutes.

This is the maximum demand charge, and understanding it is the most valuable cost idea in this entire course. Get it, and you can save serious money without turning off a single useful machine. Miss it, and you can spend a fortune on energy efficiency while the biggest lever sits untouched.

Energy versus power: the two things your meter tracks

Before we get to money, a quick refresher (covered fully in Power vs Energy: kW and kWh Explained).

- Energy is how much electricity you use over time, measured in kilowatt-hours (kWh). This is the "units" side of your bill — like the total litres of water that flowed through your tap this month.
- Power (or demand) is how fast you are drawing electricity at any instant, measured in kilowatts (kW) — like how wide the tap is open right now.

You pay for energy because the power station had to burn fuel to make it. But you also pay for demand, because the grid — cables, transformers, substations — had to be built big enough to deliver your fastest gulp, even if that gulp lasted only half an hour. That standby capacity costs TNB money whether you use it or not, so they bill you for it.

How maximum demand is measured

Your commercial meter (see How Electricity Meters Work) does something specific. All month long, it records the energy used in every consecutive 30-minute block — 48 blocks a day, roughly 1,440 blocks a month.

At the end of the month it does not average them. It finds the single largest block and throws away the rest. That one block is your maximum demand.

But that block is measured in kWh (energy over half an hour), and demand must be expressed in kW (power). To convert, you divide the energy by the length of the window in hours:

$$\text{MD (kW)} = \frac{\text{kWh in the worst 30 min}}{0.5 \text{ h}} = \text{kWh} \times 2$$

Worked example. Suppose your busiest half-hour of the entire month consumed 100 kWh. Then:

$$\text{MD} = 100 \text{ kWh} \times 2 = 200 \text{ kW}$$

That 200 kW is now your billed demand for the whole month — set by 30 minutes out of roughly 43,200.

Turning demand into ringgit

The demand charge is simply your maximum demand multiplied by a fixed rate:

$$\text{MD cost} = \text{monthly MD (kW)} \times \text{capacity/network rate (RM/kW)}$$

Under Malaysia's RP4 tariff, effective 1 July 2025, the demand-related charges for medium-voltage customers combine a capacity component and a network component:

So for our 200 kW building on the General rate:

$$200 \text{ kW} \times \text{RM}89.27/\text{kW} = \text{RM}17{,}854 \text{ per month}$$

That is RM214,248 a year — for capacity, before a single kWh of actual energy is counted. This is why the demand charge, not the energy charge, is often where the real money hides.

The number that shocks everyone: scale it up

Now picture a very large industrial customer. Its meter records a highest peak-period maximum demand of 71,700 kW. On the ToU peak combined rate:

$$71{,}700 \text{ kW} \times \text{RM}97.06/\text{kW} = \text{RM}6{,}959{,}202 \text{ per month}$$

Nearly RM7 million a month — from demand charges alone. One factory, one worst half-hour, every month.

Here is the subtle, crucial detail. Suppose the same plant had an even bigger spike of 77,380 kW — but it happened at 3 a.m., during the off-peak window. Under a time-of-use tariff, the demand charge is set by the highest demand within the peak period, not the absolute highest of the day. That midnight spike, larger though it is, is not charged. The 71,700 kW peak-period figure is what bills.

The lesson for anyone on a ToU tariff: when your peak happens matters as much as how big it is. A large draw during off-peak hours can be effectively free of demand charge, while a modest peak at 3 p.m. sets your bill.

Why chillers are usually the culprit

In most Malaysian commercial buildings, the biggest single driver of the afternoon peak is air-conditioning — specifically the chillers. On a hot day, when the whole building calls for cooling at once, compressors ramp to full load and can dominate your demand curve. (We explore this in depth in the Cooling Fundamentals course, where chiller staging and start sequencing are the main tools for shaving that peak.)

Lifts, escalators, kitchen equipment, and simultaneous motor starts pile on top. The problem is rarely that any one machine is too big — it is that too many switch on in the same half-hour.

Demand-side management: shave the peak, not the total

Because the charge is set by one peak, the strategy to reduce it is different from ordinary energy saving. This family of tactics is called Demand-Side Management (DSM), and it has three classic moves:

- Load shifting — move flexible loads to a different time. Run the ice-storage system, EV chargers, or batch equipment overnight instead of at 2:30 p.m. The total kWh is unchanged; the peak drops.
- Peak clipping — hold the top off the peak directly. Momentarily stage down non-critical loads (a few chillers, some AHUs) the instant demand approaches your target ceiling, so the meter never records the spike.
- Valley filling — deliberately use more electricity during off-peak troughs (charging thermal or battery storage) so you rely on it during peaks. This raises your average without raising your peak.

Notice that all three attack the shape of your demand curve, not its total area. That is the whole point: you can cut the demand charge without cutting useful work.

Worked example of the payoff. Our 200 kW building staggers its chiller and lift startups so its worst half-hour never exceeds 170 kW:

$$170 \text{ kW} \times \text{RM}89.27/\text{kW} = \text{RM}15{,}175.90 \text{ per month}$$

The saving is 30 kW × RM89.27 = RM2,678.10 every month, or RM32,137.20 a year — from timing, not from using less electricity overall.

Two ratios that describe your demand habits

Engineers use two simple ratios to judge how "peaky" a building is.

Demand factor compares your actual peak to the total you could draw if everything ran at once (your connected load — the nameplate sum of all equipment):

$$\text{Demand factor} = \frac{\text{Maximum demand}}{\text{Connected load}}$$

If your building has 500 kW of equipment installed but never peaks above 200 kW:

$$\text{Demand factor} = \frac{200}{500} = 0.40$$

A low demand factor means you rarely run everything together — good, and a sign there is diversity to exploit.

Load factor compares your average draw to your peak draw over the billing period:

$$\text{Load factor} = \frac{\text{Average load}}{\text{Maximum load}}$$

If your building averages 150 kW but peaks at 200 kW:

$$\text{Load factor} = \frac{150}{200} = 0.75$$

A high load factor (close to 1) means a flat, steady profile — you are getting good value from the capacity you pay for. A low load factor means brief, expensive spikes towering over a modest average: exactly the profile where peak clipping pays best. If your load factor is low, your demand charge is doing you the most damage, and DSM is your biggest opportunity.

Trimming the peak before it is recorded

The catch with manual peak management is that the "worst half-hour" can arrive with no warning — a hot afternoon, a coincidental cluster of startups — and once the meter records it, you pay for it all month. Watching a demand graph by hand and reacting in time is nearly impossible.

This is where automation earns its keep. Cobler's CobiNeural platform does threshold-based peak shaving: it watches your live demand against a target ceiling and automatically trims flexible load — briefly staging down a chiller or non-critical equipment — before the peak is recorded, then restores it once the moment passes. The building stays comfortable; the meter never sees the spike. If you want to estimate what your own peak is costing, the Maximum Demand Calculator turns your worst half-hour into a ringgit figure in seconds.

The takeaway

Your maximum demand charge is set by your single worst 30 minutes of the month, converted to kW by doubling that half-hour's kWh, and billed at roughly RM89.27 to RM97.06 per kW under RP4. Because one peak defines the whole bill, the smartest saving is not using less electricity overall — it is flattening that one spike through load shifting, peak clipping, and valley filling. On a time-of-use tariff, when your peak lands matters as much as how large it is. Watch your load factor: the peakier your profile, the more a shaved peak is worth.

Next up — Part 5: Power Factor: The Hidden Surcharge on Lazy Electricity, where we unpack the other demand-side line item that quietly inflates industrial bills.