Thailand's Energy Regulatory Commission (ERC) decided to hold the electricity rate for the September–December 2026 billing period at THB 3.95 per unit: a base tariff of THB 3.78 plus a Ft (fuel adjustment charge) of 16.23 satang. This figure does not include VAT.
The point is that this is a national average across every type of electricity user — not what you actually pay per unit. Your payback calculation should use the figure from your own bill.
Work out what you really pay in 10 seconds
Take your latest electricity bill, divide the total amount due by the number of units used that month, and the result is your home's real cost per unit.
That figure already includes everything — energy charges, the Ft, the monthly service charge and VAT. It's the only number you can genuinely use to judge value, because it's the money that actually leaves your pocket.
Thai residential electricity is priced in progressive tiers: the more you use, the more each unit costs. Homes with heavy use therefore tend to pay a higher average per unit than the figure in the news — which is why homes with high bills pay back faster than homes with low ones.
What figure we use in calculations for customers
Our calculator is set at THB 4.20 per unit, which is close to THB 3.95 plus 7% VAT and leans toward the cautious side.
We chose this on purpose, because a cautious rate keeps the payback estimate close to what you will actually see on your bills.
Three values that shape a payback estimate
- The rate per unit. Using THB 5 or more when your home actually pays about THB 4 raises the estimated savings by around 25%.
- The sunshine figure. The South gets the least sunshine of any region in the country, so for homes here we use 1,350 units per kilowatt per year rather than figures for Central or Northeastern Thailand.
- The share of power used on site. Assuming 100% isn't realistic for a home where people are out at work during the day; whatever isn't used in time is sold back at less than half the price.
If a quote doesn't state the values used for these three points, you can ask for them in writing, so that every estimate can be compared on the same basis.
Will electricity prices go up in the future?
We don't know, so our calculations use the current tariff rather than an assumed increase.
What can be said plainly is that the Ft is reviewed every 4 months, and in the latest round an option as high as THB 4.73 per unit was proposed before the decision to hold it at THB 3.95. In other words, it's a number that can move up or down. Assuming prices will rise every year therefore adds uncertainty to a payback calculation.
Sources used for this article
Figures in this article are based on public announcements and news reports (most sources are in Thai). If the conditions change, the latest official announcement from the relevant authority applies.
Frequently asked questions
Why does the news say THB 3.95, but my bill works out to THB 4.5?
Because THB 3.95 is the national average across all types of users and doesn't include VAT. Your bill uses the progressive residential tariff and includes the monthly service charge and VAT, so homes with heavy use end up with a higher average per unit.
If electricity gets cheaper in the future, will solar stop paying off?
Payback will slow down proportionally. It's a real risk that we explain to every customer, and it's why we don't recommend installing a system bigger than your actual use — the more you over-invest, the harder a drop in electricity prices hits you.
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