What Factory Electricity Costs per kWh, and Why Each Factory Pays a Different Rate

Factory electricity has no single price. The bill combines the energy charge, the monthly service charge, the Ft charge, 7% value-added tax, and, for medium-sized businesses and above, a demand charge. Prices differ by customer type, voltage level and tariff structure. For example, PEA (Provincial Electricity Authority) charges a medium-sized business on the low-voltage TOU tariff, as of Sep 2026, an On Peak energy charge of 4.3297 THB/kWh and an Off Peak energy charge of 2.6369 THB/kWh, before Ft and tax.

In PEA's low-voltage table, the Off Peak TOU energy rate is the same for small, medium and large businesses. Medium and large businesses on the TOU tariff also use the same rates for both the On Peak energy charge and the On Peak demand charge. So the gap between two factories in this group comes from their share of On Peak consumption, their On Peak demand in kW and the charges that are not billed per unit. The cost per kWh, once broken into its components, is the starting figure for assessing whether rooftop solar is worthwhile.

Two factories of similar size, and bills that do not divide out the same

A factory owner compares an electricity bill with a friend's factory of similar size. Dividing each bill total by the number of units gives a different cost per unit, even though the buildings are alike and the consumption is not very different. The gap makes it hard to price products or to assess an investment in cutting electricity costs. The natural next question is what determines each factory's cost per unit.

What does factory electricity cost per kWh, and why is there no single number?

The per-unit rates in the utilities' announcements exclude value-added tax, and a real bill contains items that are not charged per unit. Dividing the bill total by the units used therefore does not equal the announced rate.

The rate announcements of PEA and the Metropolitan Electricity Authority (MEA) state that the announced rates exclude value-added tax. PEA's announcement describes the monthly bill as electricity charged at the tariff rate, plus the Ft charge and value-added tax. For the reader, this means the figures in the rate table are only a starting point; the amount actually paid per unit must include the other items.

For medium and large businesses, the tariff charge includes an energy charge billed per unit and a demand charge billed per kW, together with a monthly service charge billed as a fixed amount per month. Two factories using the same number of units can therefore pay differently if the demand (kW) shown on their bills differs.

A cost per unit that can be compared starts with three things: the customer type, the voltage level of supply and the tariff structure. Together they form the type code in the rate announcement, which is used to pick the row in the rate table that matches the factory.

What does a factory electricity bill consist of?

A factory electricity bill consists of the energy charge, the demand charge, the monthly service charge, the Ft charge and value-added tax. Only the energy charge and the Ft charge are billed directly per unit.

**Energy charge** is billed per unit (kWh) at the rate in the table for the customer type, voltage level and tariff structure. This item grows with the number of units used. Under the TOU tariff, the price per unit differs between On Peak and Off Peak, so the same number of units can cost different amounts depending on when they are used.

**Demand charge** is billed per kW and applies only to medium-sized businesses and above. It grows with the demand (kW) shown on the bill, not with the number of units. Factories using the same number of units can therefore pay different amounts for this item.

**Monthly service charge** is a fixed amount per month that does not depend on the number of units. In a month of low usage, this item takes a larger share of the cost per unit. Small businesses on low voltage (types 2.1.2 and 2.2.2) pay a monthly service charge of 33.29 THB/month. Small businesses on medium voltage (types 2.1.1 and 2.2.1) pay a monthly service charge of 312.24 THB/month. Medium-sized businesses (type 3) have a monthly service charge of 312.24 THB/month.

**Ft charge** is billed as a rate per unit and shown as a separate line on the bill every month. This item grows with the number of units, in the same way as the energy charge.

**Value-added tax** on the bill is 7% of the base electricity charge plus the Ft charge. This item grows with the whole pre-tax amount, so every baht added to the energy charge, demand charge or service charge has tax added on top.

Which customer type is the factory, and what is it measured by?

Within business types 2–4, the customer type is set by the highest average demand over 15 minutes in the month, measured through a single meter. Medium and large businesses are further separated by average monthly electricity consumption over the previous 3 months (units per month). It is not set by building size. (Hotels and residential rental businesses in the same size range as medium and large businesses fall under type 5.)

Within business types 2–4 (hotels and residential rental businesses in the same size range as medium and large businesses fall under type 5), a small business (type 2) is a customer whose demand is below 30 kW. A large business (type 4) is a customer whose demand is 1,000 kW or more. A customer whose three-month average consumption exceeds 250,000 kWh/month also falls into the large business type. The quantity compared is the average units per month over the previous 3 months. A customer between the small and large business thresholds is a medium-sized business (type 3).

For a factory owner, this means two factories in the same area and in the same line of business can fall into different types if the demand measured by their meters differs. A different type means a different rate table, and medium-sized businesses and above have a per-kW demand charge added to the bill.

Hotels and residential rental businesses in the same size range as medium and large businesses fall under type 5, a specific business type that has its own place in the rate announcement. As for a small business whose demand goes beyond the small-business threshold in some month, it is moved up to a higher type, depending on the case.

Which voltage level is the supply, and how much do the per-unit rates differ?

The rate announcement has separate tables by voltage level of supply, and the type code shows the level in its last digit. For example, a small business on the low-voltage TOU rate is type 2.2.2, while on medium voltage it is type 2.2.1.

The type code in the rate announcement has three levels. The first digit is the customer type, the second is the tariff structure and the last is the voltage level. Small businesses have two levels, medium and low voltage, while medium and large businesses have three: high, medium and low voltage. How to read the type code printed on the bill is covered in the chapter on how to read a factory electricity bill.

A small business on the normal rate at medium voltage (type 2.1.1) is charged an energy charge of 3.9086 THB/kWh, while at low voltage (type 2.1.2) it is charged in tiers by number of units. A small business on the TOU rate at medium voltage (type 2.2.1) pays an On Peak energy charge of 5.1135 THB/kWh. The Off Peak energy charge for a small business on the TOU rate at medium voltage (type 2.2.1) is 2.6037 THB/kWh. A small business on the TOU rate at low voltage (type 2.2.2) pays an On Peak energy charge of 5.7982 THB/kWh.

The TOU rates for small businesses on medium voltage are lower than on low voltage in both On Peak and Off Peak, while the monthly service charge for small businesses on medium voltage is higher than on low voltage. As a result, for small businesses the voltage level changes both the per-unit rate and the fixed monthly amount. Comparing the cost per unit of two small factories supplied at different levels is therefore complete only when both parts are considered. For medium-sized businesses, the monthly service charge is the same at every voltage level.

At low voltage, medium businesses on the TOU rate (type 3.2.3) and large businesses on the TOU rate (type 4.2.3) use the same energy rates and the same On Peak demand rate. A large business on the TOU rate at low voltage (type 4.2.3) pays an On Peak demand charge of 210.00 THB/kW per month. The complete tables for the high-voltage and medium-voltage levels, for every type, are in PEA's electricity rate announcement.

Normal rate, TOU or TOD: which is the factory on?

Medium and large businesses that apply for new electricity service are placed on the TOU rate (types 3.2 and 4.2). The normal rate for medium businesses (type 3.1) and the TOD rate for large businesses (type 4.1) remain open only to existing customers.

The TOU rate prices the energy charge differently in the On Peak and Off Peak periods set by the announcement, while the normal rate charges a single energy rate. A medium business on the normal rate at low voltage (type 3.1.3) is charged an energy charge of 3.1751 THB/kWh. The TOU rate for medium businesses at low voltage (type 3.2.3) charges an On Peak rate higher than this rate and an Off Peak rate lower than this rate.

As a result, two factories in the same type and at the same voltage level can pay differently: one is an existing customer still on the normal rate, and the other started using electricity later and was placed on the TOU rate. For a factory on the TOU rate, the share of units used in Off Peak determines whether the average energy charge per unit ends up closer to the Off Peak rate or the On Peak rate.

Before comparing the cost per unit with another factory, find out which tariff structure the factory is on. That shows whether the gap comes from the tariff structure or from other factors. How to identify the tariff structure from the bill is covered in the chapter on how to read a factory electricity bill.

Which charges are not billed per unit but still make each factory's bill differ?

The minimum electricity charge, the power factor (PF) charge and the surcharge for a meter on the low-voltage side of the customer's transformer, under PEA's announcement, are items that are not in the per-unit rates in the table, yet they can make factories on the same rate pay differently. PEA's announcement states this surcharge under type 2.2, type 3, type 5, type 6 and type 7, and it does not appear under type 2.1 and type 4.

The minimum electricity charge is tied to the highest demand over the past 12 months, counted up to the current month. The details of how it is calculated are in the topic of the demand charge (Demand Charge).

The power factor (PF) charge is a separate item that is not in the per-unit rates in the table. The third item is the surcharge for a meter on the low-voltage side of the customer's transformer, under PEA's announcement, which is stated in the notes of type 2.2, type 3, type 5, type 6 and type 7 and does not appear under type 2.1 and type 4.

When two factories use the same row of the rate table, the bill total divided by units can still differ because of these items. Separate the amounts of these items out of the bill before comparing with another factory. That shows the difference that comes from the actual rate separately from the difference that comes from usage patterns and meter installation.

Which part of the electricity cost is the same for every factory?

The Ft charge in the same period is a fixed rate per unit that every factory pays equally, and value-added tax is charged at a single rate of 7%.

According to documents from the Energy Regulatory Commission (ERC), the Ft charge is adjusted in rounds of Jan–Apr · May–Aug · Sep–Dec and is billed every month as a separate line on the bill. The origin of the Ft charge and its effect on solar's worthwhile-ness (in Thai) is a separate subject. For comparing bills, the point is that in the same period the Ft charge per unit does not make two factories different.

The rates of PEA and MEA for the same customer type and voltage level are set equal. Factories in different utility areas can therefore compare per-unit rates, as long as the type code is read to match the format on each utility's bill.

The difference in cost per unit between factories therefore comes from the customer type, voltage level, tariff structure, share of On Peak usage and the charges that are not billed per unit. It does not come from the Ft charge or value-added tax. A factory's own cost per unit, once these components are separated, is the starting figure used to assess whether rooftop solar is worthwhile.