Demand Charge and TOU in Thailand: How Energy Monitoring Helps You See Peak Demand

PEA and MEA offer Time-of-Use (TOU) tariffs for medium and large customers. These combine energy charges that can differ by time of day with a demand charge in baht per kW. A monthly meter reading hides what drives these charges. This article explains the idea in general terms; check your own bill and the current PEA or MEA tariff for exact rates and time periods, because they are updated from time to time.

Illustration: energy management software dashboard with charts

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Your Bill

Three Things Behind the Numbers

Most medium and large customers pay for these three things together.

Energy charge (kWh)

How much electricity you used. Under TOU, the price per kWh can differ between time periods.

Demand charge (kW)

Based on your highest average power draw in a short interval during the month — typically measured over 15 minutes. Check the tariff terms for exactly how your charge is set.

Time of day

Depending on the tariff, the time period decides the energy price and whether demand counts toward the charge.

The Problem

Why a Monthly Bill Is Not Enough

The bill tells you the result. It does not tell you the cause.

1
One short spike can set the monthBecause the highest interval counts, a brief peak can set the demand charge for the whole month.
2
The bill does not show what caused itA meter that logs at short intervals shows when the peak happened and which loads were running at that time.
3
Common causes are easy to missStarting several large motors together, or running heavy equipment at the same time as production peaks, are typical examples.
4
You cannot fix what you cannot seeOnce the profile is visible, options such as staggering start-ups or moving flexible loads to another time can be tested.

With an EMS

What an Energy Management System Lets You Do

A practical routine that many sites follow once metering is in place.

1
Log power at the main meter pointRecord kW at short intervals at the incoming supply, so you can compare it with the utility's own demand figure.
2
Find the peak and what was runningUse sub-meters on large loads to see which equipment contributes most at the peak.
3
Test a changeTry one change at a time, such as staggering start-ups, and check the result in the data.
4
Review against the billEach month, compare your monitored figures with the bill to confirm what changed.

Solar and demand charge Rooftop solar reduces the energy you buy, but demand is set by the highest interval — and a cloudy moment can coincide with a high load. Monitoring shows whether your solar system is actually lowering your peak.

This article explains tariff concepts in general terms. Rates, time periods and calculation rules change and differ by tariff — always use your own bill and the current PEA or MEA schedule. Savings depend on your process and are not guaranteed.

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Demand Charge and TOU: How Energy Monitoring Helps You See Peak Demand