Total Installed Cost by System Size — 100 kW / 500 kW / 1 MW
Factory solar in Thailand 2026 costs roughly 18-25 THB per watt installed. Systems under 1 MWp run 20-25 THB/W, while 1-3 MWp systems drop to 18-22 THB/W due to economies of scale. That price covers panels, inverter, mounting, BOS, labor, permitting, and commissioning.
The table below converts the THB/W range into approximate total cost for the three sizes most common in Thai factories. Figures are advisory pre-BOI ranges for budget planning, not binding quotes. Actual cost depends on roof type, structural reinforcement, distance to switchgear, and equipment tier.
| System Size | THB/W (installed) | Approx. Total Cost | Notes |
|---|---|---|---|
| 100 kWp | 22-25 THB | ~THB 2.2-2.5M | Highest labor + permit per watt |
| 500 kWp | 20-23 THB | ~THB 10-11.5M | Soft costs start to fall per watt |
| 1 MWp | 18-22 THB | ~THB 18-22M | Lowest labor/design/permit per watt |
Ranges are advisory for budget planning, not binding quotes. For detailed size-by-size pricing, see the 2026 factory solar price guide.
Where the Money Goes: the 7-Part Cost Stack
A single turnkey price is made of 7 parts. The shares below are 2026 Thai industry averages that shift with system size, roof type, and equipment tier. The line item to watch is labor (ค่าแรง) — the part most often overlooked in a quote.
1. Solar panels (modules)
The single largest share. n-type TOPCon 565-580 W panels are mainstream in 2026; falling panel prices have shrunk this share versus prior years.
2. Inverter
50-125 kW string inverters from brands such as Huawei, Sungrow, and SMA. Spec and unit count depend on the designed DC/AC ratio.
3. Mounting / racking
Galvanized steel + aluminum rail for sawtooth, flat, or metal-sheet roofs. Cost shifts with roof type and wind-load requirement.
4. BOS (cabling / switchgear / monitoring)
Balance of System: DC/AC cabling, MCB + SPD, bi-directional meter, monitoring, and grounding. The farther from the switchgear, the higher the BOS cost.
5. Installation labor (ค่าแรง)
The most overlooked line item. Labor covers the install crew, scaffolding, cranes, working-at-height safety, and 8-12 weeks of work. Labor per watt varies most with roof type, height, and site distance.
6. Permits
PEA/MEA permits, interconnection, relevant building/factory licenses, and BOI paperwork are largely fixed per project, so they average cheaper per watt as the system grows.
7. Commissioning + testing
System testing, performance-guarantee tests, inverter commissioning, and as-built handover — the final step before the system goes live.
Note: shares sum to roughly 100% and shift with size — labor and permits average lower per watt on larger systems. For the panel-price and EPC trend behind these numbers, see why module prices fell from 2024 to 2026.
Why Installation Labor Cost Varies So Much
Labor (ค่าแรง) is the hardest part of the cost to predict because it depends on the actual site. The 5 drivers below can make labor-per-watt differ by up to 2x between two factories of the same size.
Roof type
Metal sheet installs faster than concrete or sawtooth roofs, which need more anchoring and waterproofing. Sawtooth roofs take the most time and labor.
Height
Taller roofs require scaffolding, cranes, and added working-at-height safety measures, which raise both labor and time.
Structural reinforcement
If the existing roof cannot carry the 15-20 kg/m² distributed load, steel-beam reinforcement or roof replacement is needed, sharply raising both labor and materials.
Site distance
Sites far from the city or from the switchgear raise travel, freight, and cable-run time, pushing up both labor and BOS.
Crew size & experience
Manufacturer-trained EPC crews with factory experience install faster and more safely, cutting both time and rework risk.
Economies of Scale: Why THB/W Drops as Size Grows
A 1 MW system typically costs about 10-15% less per watt than a 100 kW system because several cost components are fixed per project, not per watt. Spread across more watts, the average per-watt cost falls.
Labor & design
Crew and most design steps are fixed costs. Installing 1 MW does not need 10x the crew of 100 kW, so labor-per-watt falls.
Permits & soft costs
PEA/MEA permits and BOI paperwork are per-project costs, so they average markedly cheaper per watt on a larger system.
Procurement & freight
Bulk module and inverter orders secure better unit pricing, and freight averages lower per watt.
Caveat: economies of scale are not always linear. If the roof needs heavy structural reinforcement or the build is phased, per-watt cost may not fall proportionally.
How Install Cost Feeds Into Payback
Install cost (CapEx) is the numerator in a payback calculation; the denominator is the electricity bill saved per year. The lower the cost per watt and the higher the tariff, the shorter the payback. Most Thai factories land around 4-6 years.
Tariff context (per ERC May-Aug 2026): average tariff ~3.95 THB/kWh, Ft 0.1623 THB/kWh, TOU Type 4 on-peak 5.27 / off-peak 3.80 THB/kWh (before 7% VAT). Factories with heavy daytime on-peak load save the most when solar generates midday.
Want your own factory's payback? open the ROI calculator.
Or see a detailed factory payback worked example in the factory solar ROI guide.
Why Cost Estimates Should Come from a Proven EPC
Cost-per-watt numbers only mean something when they come from a team that has installed in many real-world roof conditions. CapSolar estimates from actual project experience, not a generic spreadsheet.
80+ MWp installed · 150+ projects · 100+ clients · 85,000+ tons CO₂ avoided
Want size-by-size pricing or to prep procurement? See the 2026 factory solar price guide / solar EPC guide.
Get an Install-Cost Estimate for Your Factory
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