If you’re running a factory in Thailand, your electricity bill probably looks like it’s been designed by someone who enjoys making life complicated. And in a way, it has. The Electricity Generating Authority of Thailand (EGAT) and the Metropolitan/Provincial Electricity Authorities (MEA/PEA) structure rates so that what you pay per unit changes depending on when you use it, how much you use at once, and what type of customer you are.
This is called a Time of Use (TOU) tariff, and it’s the single most important concept for understanding why solar panels are such a good financial fit for Thai businesses.
Here’s the thing most consultants don’t tell you upfront: solar panels don’t just produce “free electricity.” They produce free electricity at exactly the wrong time to be useless — which, for Thai factories, happens to be exactly the right time.
Let me explain.
What Is Thailand’s TOU Tariff?
Thailand applies different electricity rates to different customer types. For most medium and large industrial and commercial users — which includes basically every factory — the TOU (Time of Use) rate applies.
Under TOU pricing, the day is divided into two periods:
On-Peak Period
Time: Monday–Friday, 09:00–22:00 (9 AM to 10 PM)
This is when the grid is under the most stress, and when you pay the most per unit.
Off-Peak Period
Time: Monday–Friday, 22:00–09:00, plus all day Saturday, Sunday, and public holidays
This is when electricity is significantly cheaper.
Current TOU Rates for Large Industrial Users (2025-2026)
For large industrial customers (TOU rate, voltage ≥ 69kV), the approximate rates are:
- On-Peak energy charge: ~THB 3.40–3.80 per kWh
- Off-Peak energy charge: ~THB 1.90–2.30 per kWh
- Demand charge: ~THB 126–189 per kW per month
(Rates fluctuate with the Ft charge mechanism. Check the latest MEA/PEA schedule for exact figures.)
For smaller commercial and industrial users (medium voltage, 12–69kV), rates are slightly higher on the energy charge side but follow the same TOU structure.
The Key Number: On-Peak vs Off-Peak Spread
The on-peak rate is typically 60–80% higher than the off-peak rate. That’s a massive spread. And here’s why it matters for solar:
Solar panels produce their peak output between 10:00 AM and 3:00 PM — squarely inside the on-peak period.
Every kilowatt-hour your solar system produces during those hours is displacing electricity that would otherwise cost you the on-peak rate. That’s THB 3.40–3.80 per kWh you’re not paying, versus the off-peak rate of THB 1.90–2.30.
Why This Timing Is Solar’s Secret Weapon
Let’s do the math that matters.
A Factory Example: 500 kW Rooftop System
Imagine a mid-sized manufacturing facility in Rayong province running one production shift, 08:00–17:00, Monday through Friday. Their monthly electricity consumption is roughly 200,000 kWh, and they’re on the TOU rate.
Without solar:
During peak production hours (10:00–15:00), the factory is consuming a large chunk of its daily electricity — let’s say 60% of daily usage falls in the on-peak period. At an on-peak rate of ~THB 3.60/kWh (midpoint estimate including Ft), that’s a lot of money going to MEA/PEA every month.
With a 500 kW solar system:
A 500 kW system in Thailand produces approximately 1,800–2,100 kWh per day, depending on season. Almost all of that generation happens between 07:00 and 18:00, with the peak between 10:00 and 15:00.
Here’s the critical point: approximately 85–90% of the solar generation occurs during on-peak hours.
That means the displaced electricity — the “savings” — is valued at the on-peak rate, not some average of on-peak and off-peak. This timing advantage adds roughly 30–40% more value to the solar investment compared to a flat-rate scenario.
Monthly savings estimate:
- Solar production: ~55,000 kWh/month (conservative, 500 kW × 3.7 kWh/kWp/day × 30 days × 0.85 system efficiency)
- Displaced on-peak electricity: ~48,000 kWh (85% of production falls in on-peak)
- Savings on on-peak: 48,000 × THB 3.60 = THB 172,800/month
- Savings on off-peak: 7,000 × THB 2.10 = THB 14,700/month
- Total monthly savings: ~THB 187,500
- Annual savings: ~THB 2,250,000
For a system costing approximately THB 12–15 million, the payback period lands at 5.3–6.7 years — and after that, you’ve got 18–20 more years of essentially free on-peak electricity from a 25-year-warrantied system.
The Demand Charge Bonus
There’s another angle that gets even less attention: demand charges.
TOU tariffs include a monthly demand charge based on the highest 15-minute peak demand recorded during the billing period (measured in kW). For many factories, this peak occurs during the on-peak hours on hot afternoons — precisely when air conditioning loads spike and production is in full swing.
Solar panels can reduce your recorded peak demand by generating electricity during these exact hours. A well-sized system might shave 200–400 kW off your peak demand, saving:
- 300 kW × THB 157/kW (approximate demand charge) = THB 47,100/month in demand charge savings
This is in addition to the energy charge savings calculated above. Most factory owners don’t even realize this is happening until they see the bill.
Seasonal Variations — The Thai Climate Advantage
Thailand’s weather pattern creates an interesting alignment that most other countries can’t match:
Hot Season (March–May)
- Highest electricity demand due to air conditioning
- Solar irradiance at its peak (5.5–6.5 kWh/m²/day)
- Maximum solar production + maximum electricity rates (Ft tends to be higher)
- This is when solar saves you the most money per month
Rainy Season (June–October)
- Lower solar output (cloud cover reduces production by 15–30%)
- But grid electricity demand is also lower
- Ft charges may be adjusted downward
Cool Season (November–February)
- Good solar conditions (clear skies, lower temperatures improve panel efficiency)
- Moderate electricity consumption
- Solid, predictable production
The net effect: Thailand’s solar production profile correlates positively with electricity pricing. When the grid is most expensive, your panels produce the most. When production drops (rainy season), the grid is cheaper anyway.
This natural hedging is one reason why solar ROI calculations in Thailand tend to be more stable than in markets where solar output and electricity pricing are misaligned (like Germany, where peak production happens in summer but peak consumption is in winter for heating).
The Ft Charge Factor — Your Hidden Cost Variable
The Ft (Fuel Adjustment Charge) is a mechanism that adjusts electricity rates based on fuel costs, exchange rates, and other factors. It’s added on top of the base energy charge and changes approximately every 4 months.
Why Ft Matters for Solar ROI
Over the past decade, the Ft charge has generally trended upward due to rising natural gas prices (Thailand generates about 60% of its electricity from gas). When Ft goes up, your grid electricity gets more expensive — but your solar savings increase proportionally.
Recent Ft charges have been in the range of THB 0.20–0.40 per kWh, adding a significant percentage on top of the base rate.
Solar as a hedge: By installing solar, you’re effectively locking in a fixed cost per kWh for the next 25 years. While your neighbors watch their electricity bills creep up every Ft adjustment period, your solar production cost stays flat.
Historical data suggests that Thailand’s average electricity rate has increased by approximately 2–4% per year over the past decade. If this trend continues, a solar system that pays back in 6 years at today’s rates might pay back in 5.5 years when you factor in rate escalation — and the total 25-year savings could be 20–30% higher than a static calculation suggests.
Solar + TOU: Strategies to Maximize Your Savings
Understanding the TOU structure lets you optimize beyond just slapping panels on the roof.
Strategy 1: Size for Maximum Self-Consumption During On-Peak
Don’t just size your system to cover your total monthly consumption. Size it to cover your on-peak daytime consumption. Excess production that falls outside on-peak hours or exceeds your consumption is still valuable but at a lower rate.
A system that produces 90% of its output during on-peak hours and displaces on-peak consumption is worth more than a larger system where 40% of production goes unused or offsets cheaper off-peak rates.
Strategy 2: Shift Loads to Daytime
If your operations allow it, shifting energy-intensive processes to daytime hours (when solar is producing) dramatically increases the value of each kWh. Running heavy machinery, charging EV fleets, or powering cold storage during 10:00–15:00 instead of early morning or evening means more solar displacement at on-peak rates.
Strategy 3: Add Battery Storage for Peak Shaving
Battery energy storage adds another layer of optimization. Charge batteries from excess solar during midday, then discharge during the late on-peak hours (17:00–22:00) when solar has dropped but rates are still at the on-peak level.
This is especially valuable for factories with evening shifts — you can extend solar savings well beyond sunset.
Strategy 4: Monitor Your Demand Charge Peak
Set up real-time monitoring to track your 15-minute demand peaks. When you see demand approaching a new monthly high, ensure your solar system is performing optimally (clean panels, inverter functioning). Even small improvements in solar output during a peak demand moment can save thousands of baht on the demand charge.
What This Means for the EMC Model
If you’re considering the Energy Management Contract (EMC) model — where Red Solar invests, builds, and operates the system while you buy electricity at a discount — the TOU tariff makes this even more attractive.
Because the solar company bears the performance risk, they’ll size and orient the system to maximize on-peak production. You get a discount on the electricity you’d otherwise pay at the on-peak rate, with zero upfront investment.
The typical EMC discount in Thailand is 10–20% below the grid rate. For on-peak electricity at THB 3.60/kWh, that’s a discount of THB 0.36–0.72 per kWh. On 48,000 kWh of monthly on-peak displacement, that’s THB 17,280–34,560 per month in savings with zero investment.
Common Misconceptions About TOU and Solar
“Solar won’t work during rainy season”
It will. Yes, production drops by 15–30% during heavy cloud cover, but it doesn’t stop. And Thailand’s rainy season rarely means all-day rain — most rain comes in afternoon showers, meaning morning solar production remains solid. Annual production factors of 1,300–1,500 full-load hours are standard for Thailand.
“The demand charge is too small to matter”
For a medium-to-large factory, the demand charge can represent 15–25% of the total electricity bill. Solar reducing peak demand is a real, measurable savings component — not a rounding error.
“I should size my system to cover 100% of consumption”
Not necessarily. The last few kW of capacity might produce excess during off-peak hours, displacing cheaper electricity. The optimal system size often covers 70–85% of daytime on-peak consumption, not 100% of total consumption. Beyond that point, the marginal return decreases.
The Bottom Line
Thailand’s TOU tariff structure is one of the best things that could happen to the business case for rooftop solar. The pricing model aligns perfectly with solar’s production profile: expensive electricity when the sun is shining, cheaper electricity when it isn’t.
For factory owners, this means:
- Higher per-kWh savings than flat-rate markets
- Faster payback periods (typically 4–7 years in Thailand)
- Built-in inflation protection as Ft charges rise over time
- Additional demand charge savings that most owners overlook
- Seasonal alignment where Thailand’s hot season delivers maximum production when electricity is most expensive
If you haven’t analyzed your electricity bill through the TOU lens yet, you’re probably leaving money on the table.
Get a Free Solar Assessment — We’ll analyze your consumption pattern, identify your on-peak usage, and calculate exactly how much a rooftop solar system would save under Thailand’s TOU tariff.
