How to Read Your PEA/MEA Electricity Bill for Solar Planning: A Thai Factory Owner’s Guide to Calculating Solar Savings from Your Monthly Invoice
Every month, your factory in Thailand receives an electricity bill from PEA or MEA. Most business owners glance at the total amount, pay it, and move on. But hidden inside that invoice is a goldmine of data — data that tells you exactly how much money a rooftop solar system would save your business, how quickly it would pay for itself, and which system size makes the most financial sense.
The problem? Thai electricity bills are not written for normal humans. They look like tax forms designed by accountants who hate clarity.
This guide changes that. By the time you finish reading, you’ll be able to open your latest electricity bill, find the critical numbers, and calculate a rough solar ROI estimate without calling anyone. You’ll understand what every charge means, which ones solar eliminates, and which ones stick around even after you go solar.
Let’s get into it.
Which Utility Provider Matters for Your Factory
Thailand has two main electricity distribution authorities, and which one bills you depends entirely on where your facility is located:
- MEA (Metropolitan Electricity Authority) — Serves Bangkok, Nonthaburi, and Samut Prakan. If your factory is in any of these three provinces, you get MEA bills.
- PEA (Provincial Electricity Authority) — Serves all other 74 provinces in Thailand. That means Rayong, Chonburi, Chachoengsao, Ayutthaya, Pathum Thani, and virtually every industrial estate outside the Bangkok metro area falls under PEA.
For solar planning purposes, the distinction matters because MEA and PEA use slightly different tariff codes and billing formats. The core structure is similar — both follow the TOU (Time of Use) system for medium and large consumers — but the line items and specific rate numbers differ.
Most factory owners in Thailand’s key industrial provinces (Rayong, Chonburi, Eastern Seaboard) deal with PEA. This guide focuses primarily on PEA bills, with MEA differences noted where relevant.
If you’re unsure which provider serves your location, check your bill header. PEA bills say “การไฟฟ้าส่วนภูมิภาค” while MEA bills say “การไฟฟ้านครหลวง.”
The Five Numbers That Matter for Solar
Your electricity bill has dozens of line items, but only five drive the solar savings calculation. Everything else is noise. Here’s what to look for:
1. Energy Charge (kWh Usage) — The Big One
This is the largest single component of your bill and the first place solar attacks.
On a PEA bill for a medium/large factory on TOU tariff, look for a section showing energy consumption broken into two periods:
- On-Peak (Peak) kWh — Electricity used during peak hours: Monday to Friday, 09:00-22:00
- Off-Peak kWh — Electricity used during off-peak hours: Monday to Friday, 22:00-09:00, plus all day Saturday, Sunday, and public holidays
The current rates (as of early 2026) are approximately:
- On-Peak: ~THB 4.70-5.50 per kWh
- Off-Peak: ~THB 2.70-3.10 per kWh
To find your on-peak kWh usage, look for the line item showing “หน่วย On-Peak” or “On-Peak Unit” on your bill. This is the number to use when sizing your solar system.
2. Demand Charge (kW) — The One Solar Doesn’t Eliminate
Demand charge appears on TOU tariff bills and is calculated based on your highest 30-minute power demand during on-peak hours, measured in kilowatts (kW).
The rate is approximately THB 56-64 per kW of peak demand per month (MEA and PEA differ slightly).
This is a common mistake factory owners make when evaluating solar ROI: assuming the demand charge disappears. It doesn’t. Budget conservatively.
3. Service Charge — Fixed Monthly Cost
This is a fixed fee simply for being connected to the grid:
- PEA (voltage level 22-33 kV): ~THB 330-1,100/month depending on voltage
- PEA (voltage level 69 kV+): ~THB 2,100/month
- MEA (similar voltage tiers): Comparable rates
4. Ft Charge (Fuel Adjustment) — The Variable Swing
The Ft (Float time) charge is a variable adjustment that reflects changes in fuel costs for power generation. It’s calculated per kWh and adjusts every four months based on EGAT’s fuel cost projections.
The Ft rate has fluctuated significantly in recent years:
- 2022 energy crisis peak: Ft exceeded THB 2.50/kWh
- 2024-2025: Ft stabilized around THB 0.10-0.30/kWh
- 2026: Current Ft rates are in the moderate range
5. VAT — The Final 7%
Thailand’s 7% VAT applies to the total of all the above charges. Since VAT is a percentage of the subtotal, it scales with everything else. When you reduce your energy charge through solar, your VAT bill drops proportionally too.
A Real PEA Bill Breakdown: What a 500kW Factory Owner Sees
Let’s walk through a realistic example. Take a medium-sized factory in Amata Nakorn Industrial Estate, Chonburi Province, operating on PEA TOU tariff with a 500 kW connection. Here’s what a typical monthly bill looks like:
| Charge | Calculation | Amount (THB) |
|---|---|---|
| On-Peak Energy | 180,000 kWh × THB 5.10/kWh | 918,000 |
| Off-Peak Energy | 60,000 kWh × THB 2.90/kWh | 174,000 |
| Demand Charge | 420 kW × THB 60/kW | 25,200 |
| Service Charge | Fixed (33 kV) | 1,100 |
| Ft Adjustment | 240,000 kWh × THB 0.20/kWh | 48,000 |
| Subtotal | 1,166,300 | |
| VAT (7%) | 81,641 | |
| **Total** | **1,247,941** |
Now, what happens if this factory installs a 500 kW rooftop solar system?
A well-designed 500 kW system in Chonburi generates approximately 650,000-750,000 kWh per year, or roughly 54,000-62,500 kWh per month. Let’s use a conservative 55,000 kWh/month, all produced during on-peak daylight hours.
| Item | Before Solar | After Solar (55,000 kWh offset) | Monthly Savings |
|---|---|---|---|
| On-Peak Energy | 918,000 | 637,500 (125,000 × 5.10) | 280,500 |
| Ft on offset kWh | Included above | — | 11,000 (55,000 × 0.20) |
| VAT on savings | ~20,405 | ||
| **Total Monthly Savings** | **~311,905** |
That’s roughly THB 3.74 million per year in savings from a system that costs approximately THB 12-15 million to install (at 2026 market rates of THB 24-30 per watt for a turnkey commercial installation). Simple payback: 3.2 to 4.0 years. Over a 25-year system life, the net savings exceed THB 75 million after accounting for maintenance costs and panel degradation.
These are real numbers. Not projections. Not marketing. This is what the math looks like when you read the bill properly.
How to Size Your Solar System Using Your Electricity Bill
You don’t need a solar engineer to estimate the right system size. You need your last three electricity bills and a calculator.
Pull your last three PEA or MEA bills and write down the on-peak kWh from each. Add them together and divide by three. This gives you a rough average. Don’t use just one month — seasonal variation in Thailand is significant, and a single bill might mislead you.
This is the percentage of your on-peak consumption that happens during daylight hours (roughly 07:00-17:00). Most factories running standard shifts consume 60-80% of their on-peak electricity during daylight. You can estimate this by looking at your production schedule: if your main machinery runs during the day and slows down at night, your daytime factor is probably 70-80%. If you run 24/7 with three shifts, it might be closer to 40-50%.
A solar system in Thailand produces roughly 1,200-1,500 kWh per year per kW installed (the exact number depends on your province’s solar irradiation). In Rayong and Chonburi, plan for approximately 1,350 kWh/kW/year, or about 112 kWh/kW/month.
If your average monthly daytime consumption is 55,000 kWh, divide by 112: that gives you a system size of roughly 490 kW. Round to 500 kW.
Now the only question is whether you have enough roof space. As a rule of thumb in Thailand, you need approximately 8-10 square meters per kW of installed capacity (accounting for panel spacing, walkways, and inverter placement). A 500 kW system needs roughly 4,000-5,000 square meters of usable rooftop.
If your roof is smaller than that, don’t panic — you can still install a smaller system and capture a portion of the savings. Even 200 kW on a limited roof generates meaningful returns. For more on sizing options, check our detailed guide comparing different system sizes for Thai factories.
Common Mistakes When Reading Electricity Bills for Solar
Mistake #1: Using Total kWh Instead of On-Peak kWh
Solar only replaces on-peak consumption. If you size your system based on total monthly usage (on-peak plus off-peak), you’ll overestimate both the system’s output and the savings. Always use on-peak kWh as your baseline.
Mistake #2: Ignoring Seasonal Variation
Thailand’s three seasons create significant solar production variation:
- Hot season (March-May): Highest solar production, highest electricity demand (AC usage)
- Rainy season (June-October): Lower solar production (cloud cover), moderate electricity demand
- Cool season (November-February): Moderate solar production, lowest electricity demand
A single month’s bill from November won’t give you the right picture. Use at least three months, ideally spanning different seasons.
Mistake #3: Forgetting About Demand Charges
As mentioned above, demand charges don’t disappear with solar. If you’re comparing a solar quote that claims to eliminate 90% of your electricity bill, ask whether they’ve accounted for the demand charge. A reputable provider will show you both scenarios — with and without demand charge reduction.
Mistake #4: Not Checking Voltage Level
Your tariff structure depends on your connection voltage. Factories connected at 22-33 kV get one rate schedule; those at 69 kV and above get another. The rates are different, and the Ft charge calculation varies too. Make sure you’re comparing the right tariff when looking at PEA or MEA rate tables online.
Why Your Electricity Bill is Your Best Sales Pitch
Here’s something most solar salespeople won’t tell you: you can do 80% of the solar investment analysis yourself, before anyone ever visits your factory.
Open your latest PEA or MEA bill. Find the on-peak kWh number. Multiply it by the current on-peak rate. That’s your monthly on-peak energy cost. Now estimate how much of that your solar system would offset (typically 60-80% of daytime on-peak usage). The savings number you get is real — it’s not an estimate, not a projection. It’s math.
When a solar provider comes to your factory with a proposal, you already know whether the numbers make sense. You’ve done the homework. You can ask informed questions about demand charge assumptions, Ft rate projections, and system degradation.
That’s the difference between being sold to and buying smart.
Getting Professional Help
Reading your electricity bill gets you 80% of the way there. The remaining 20% requires a proper site survey, structural analysis, shading study, and detailed financial modeling — all things Red Solar Thailand’s engineering team provides as part of our free consultation.
If you’ve looked at your PEA or MEA bill and want to know what a solar system would actually cost and save for your specific factory, we’re happy to run the numbers. No pressure, no obligation — just real numbers based on your actual electricity consumption.
Contact Red Solar Thailand for a free solar assessment. Our Rayong-based engineering team covers all of Thailand’s industrial provinces and can typically complete a site survey within one week of your inquiry.
Want to dive deeper? Read our guides on Thailand’s TOU tariff system, how much a 500kW system saves, and the 4 solar business models available in Thailand.
