C
CapSolar
THENZH
BOI 3/2568 · WORKED EXAMPLE · 3 SCENARIOS

BOI Solar Factory Thailand 2026 Worked Examples Without BOI

Since 1 July 2025, solar a factory installs for its own use no longer gets BOI promotion (Announcement 3/2568), so every number here is computed without BOI — 100 kW pays back in about 7.2 years · 500 kW about 5.3 · 2 MW about 5.6. Plus year-by-year cash flow, the old terms for pre-July 2025 filers, and the PPA structure.

100 kW · 500 kW · 2 MWYear-by-year · 8 yrSelf-use BOI benefit = 0
Run my factory's numbersAsk CapSolar to assess
8-min read · Updated 2026-10-05 against BOI Announcement 3/2568
Important note

Figures are illustrative, pre-tax estimates from the assumptions stated on the page — not tax advice. The BOI position summarises published Board of Investment announcements; check the latest on boi.go.th and ask BOI about your case.

How much does BOI still save on factory solar? (3 factory sizes)

For solar a factory installs for its own use and applies for from 1 July 2025: zero. BOI Announcement 3/2568 stopped promotion for installing solar power systems under the alternative-energy efficiency measure. Without BOI, at THB 3.86/kWh: a 100 kW factory pays back in about 7.2 years (pre-tax IRR 12.6%) · 500 kW about 5.3 years (18.0%) · 2 MW about 5.6 years (17.0%). The "8-year BOI tax exemption" often quoted belongs to businesses selling renewable power (7.1.2), not to factories using their own power.

1. Three real scenarios — computed without BOI

Each card shows inputs, year-by-year savings for the first 8 years, payback and IRR. CAPEX from CapSolar EPC internal quotes 2026Q1. Tariff THB 3.86/kWh for Sep–Dec 2026 from tariff-period (ex-VAT). Panel degradation 0.5%/yr. 25-year pre-tax IRR in two cases: flat tariff, and tariff +3%/yr (the same assumption as our solar calculator).

As of Sep–Dec 2026

Small factory · 100 kW · CapEx ~THB 3.1M

Small food / plastics / packaging SME · roof 500-900 m² · monthly bill 30-80K THB

Inputs (fixed assumptions)
CAPEX
฿3.10M
THB/Wp
31
Generation / yr
149,000 kWh
Self-consumption
85%
Tariff (THB/kWh)
3.86
O&M / yr
฿60K
Year-by-year net savings (first 8 years, flat tariff)
YearSavingsNetCumulative (after CAPEX)
1฿486K฿426K−฿2.67M
2฿484K฿424K−฿2.25M
3฿482K฿422K−฿1.83M
4฿479K฿419K−฿1.41M
5฿477K฿417K−฿992K
6฿474K฿414K−฿578K
7฿472K฿412K−฿166K
8฿470K฿410K฿244K
Results (no BOI)
Year-1 bill savings
฿489K
Net after O&M
฿429K
Simple payback
7.2 yr
Cumulative cash turns positive in year
8
25-yr IRR (flat tariff)
12.6%
25-yr IRR (tariff +3%/yr)
16.4%
BOI benefit (filed from 1 Jul 2025)
฿0
Old CIT ceiling (filed by 30 Jun 2025 only)
฿1.50M
This tier fits you if…
  • Monthly bill 30-80K THB
  • Roof < 700 m²
  • Mostly daytime load (self-consumption ≥ 85%)
  • Below 69 kV you pay more per kWh than the average used here — payback is shorter than shown
CapSolar EPC internal quotes 2026Q1 · World Bank Global Solar Atlas (149k kWh/100kW·yr, Central Thailand PVOUT) · tariff: tariff-period.ts blendedAvg

Mid-size factory · 500 kW · CapEx ~THB 12.5M

Mid-auto / textile / food-beverage factory · roof 3,000-5,000 m² · monthly bill 80-400K THB

Inputs (fixed assumptions)
CAPEX
฿12.50M
THB/Wp
25
Generation / yr
745,000 kWh
Self-consumption
90%
Tariff (THB/kWh)
3.86
O&M / yr
฿227K
Year-by-year net savings (first 8 years, flat tariff)
YearSavingsNetCumulative (after CAPEX)
1฿2.58M฿2.35M−฿10.15M
2฿2.56M฿2.34M−฿7.82M
3฿2.55M฿2.32M−฿5.49M
4฿2.54M฿2.31M−฿3.18M
5฿2.52M฿2.30M−฿887K
6฿2.51M฿2.28M฿1.40M
7฿2.50M฿2.27M฿3.67M
8฿2.49M฿2.26M฿5.93M
Results (no BOI)
Year-1 bill savings
฿2.59M
Net after O&M
฿2.36M
Simple payback
5.3 yr
Cumulative cash turns positive in year
6
25-yr IRR (flat tariff)
18.0%
25-yr IRR (tariff +3%/yr)
21.8%
BOI benefit (filed from 1 Jul 2025)
฿0
Old CIT ceiling (filed by 30 Jun 2025 only)
฿6.25M
This tier fits you if…
  • Monthly bill 80-400K THB
  • Roof 3,000-5,000 m²
  • 2-3 shift operation · self-consumption > 85%
  • Candidate for expansion to 1 MW+ within 3 years
CapSolar EPC internal quotes 2026Q1 (3 quotes averaged) · World Bank Global Solar Atlas · tariff: tariff-period.ts blendedAvg

Large factory · 2 MW · CapEx ~THB 54M

Large electronics / cold-chain / tier-1 automotive · roof 10,000-18,000 m² · monthly bill > 800K THB

Inputs (fixed assumptions)
CAPEX
฿54.00M
THB/Wp
27
Generation / yr
2,980,000 kWh
Self-consumption
92%
Tariff (THB/kWh)
3.86
O&M / yr
฿870K
Year-by-year net savings (first 8 years, flat tariff)
YearSavingsNetCumulative (after CAPEX)
1฿10.53M฿9.66M−฿44.34M
2฿10.48M฿9.61M−฿34.73M
3฿10.42M฿9.55M−฿25.18M
4฿10.37M฿9.50M−฿15.68M
5฿10.32M฿9.45M−฿6.23M
6฿10.27M฿9.40M฿3.17M
7฿10.22M฿9.35M฿12.52M
8฿10.17M฿9.30M฿21.82M
Results (no BOI)
Year-1 bill savings
฿10.58M
Net after O&M
฿9.71M
Simple payback
5.6 yr
Cumulative cash turns positive in year
6
25-yr IRR (flat tariff)
17.0%
25-yr IRR (tariff +3%/yr)
20.8%
BOI benefit (filed from 1 Jul 2025)
฿0
Old CIT ceiling (filed by 30 Jun 2025 only)
฿27.00M
This tier fits you if…
  • Monthly bill > 800K THB
  • Roof > 10,000 m² or ground-mount available
  • 24×7 or 3-shift operation · self-consumption > 90%
  • Large enough to compare EPC and PPA side by side
CapSolar EPC internal quotes 2026Q1 · World Bank Global Solar Atlas · tariff: tariff-period.ts blendedAvg

"Old CIT ceiling" applies only to applications filed by 30 Jun 2025: 50% of the counted investment (filed from 1 Nov 2024: counted at most THB 30M/MW). The benefit actually received equals the existing business's tax in the 3 exempt years, up to that ceiling. The 100 kW case (THB 31/Wp) exceeds the THB 30M/MW cap, so only THB 3.0M counts.

2. Which BOI route fits your situation

Summarised from Announcements 15/2565, 12/2567, 3/2568, 9/2565 and 8/2565. Details and links to the originals: current BOI solar status.

Your situationRoute / benefitWhat to do
Factory installing solar for own use, nothing filed yetNone — promotion stopped for applications from 1 Jul 2025 (3/2568)Decide on the no-BOI payback (tables above)
Filed by 30 Jun 2025 and holding a certificate15/2565 §1.4: machinery import-duty exemption + 3-yr CIT on existing-business income, ≤50% of investmentComplete within 3 years of the certificate date and follow its conditions
Solar application filed 5–30 Jun 2025Old rules, but no extension to accept the resolution or submit certificate evidenceAct within the original deadlines
Adding battery storage (BESS)BESS + inverter cap THB 12M/MW (3/2568 cl. 3) · eligibility per BOI criteriaAsk BOI before planning around it
Developer selling solar power (PPA), ≥200 kW per distribution pointActivity 7.1.2, Group A2: 8-yr CIT ≤100% of investment + machinery import dutyThe developer files, not the factory
SME (measure 5/2568)UNKNOWN whether it covers solarConfirm with BOI first

3. EPC vs PPA — who gets what

After 3/2568, the BOI difference comes down to who owns the system and what business they are in. See what is PPA and EPC vs PPA; for the cost of each funding route see the 4-way financing matrix.

ItemEPC (self-invest)PPA
System ownerFactoryDeveloper / SPV
Factory CAPEX100%THB 0
Bill savingsAll to the factoryGap between grid tariff and PPA price
BOI positionNone for applications from 1 Jul 2025If it meets 7.1.2 (≥200 kW per distribution point), the A2 benefit is the developer's
Effect on the PPA price—A commercial negotiation — not set by BOI

4. How to calculate factory solar payback without BOI

The same 5 steps used to build the tables on this page — plug in your own factory's numbers.

  1. 1. Annual generation

    Installed kWp × annual yield per kWp at your site (this page uses 1,490 kWh/kWp/yr).

  2. 2. Self-consumed kWh × tariff

    Multiply by the self-consumed share (85–92% here) and by your tariff — this page uses THB 3.86/kWh (all-class average, ex-VAT).

  3. 3. Subtract O&M

    That gives year-1 net savings.

  4. 4. CAPEX ÷ net savings

    = simple payback. The year-by-year table also applies 0.5%/yr panel degradation.

  5. 5. Check whether any BOI route applies

    For self-use solar filed from 1 Jul 2025 there is none — see the route table here and the current BOI solar status.

5. Calculate for your specific factory

Run our Solar Calculator with your real bill, or see the payback sensitivity by load pattern. For a review of your real load data and an EPC vs PPA comparison, contact CapSolar.

Solar calculatorCurrent BOI solar status

Related articles

BOI solar status — what changed (3/2568)1 MW Factory Solar Price · 3 BOMsFactory Solar ROI · 3-Shift 24×7Financing 4-Way · Cash/Loan/Lease/PPAWhat is a Solar PPAThailand Factory Electricity TariffRayong / EEC · 7-Estate GuideFactory Solar Guide (primer)Bangkok 600 kWp worked paybackCompare 4 PPA ProvidersEEC Solar Guide — complete corridor overview

Want your factory's payback without BOI?

Get a free calculationSolar calculator
CAPSOLAR HUB · FACTORY SOLAR

Back to the Master Guide

This page is one of 15 topics in the Factory Solar Thailand 2026 master hub — Assess → Design → Finance → Operate.

Open the hub

Frequently Asked Questions (numeric)

Sources & References

  1. ประกาศคณะกรรมการส่งเสริมการลงทุน ที่ 3/2568 — BOI Announcement 3/2568 (Thai, official)
  2. ประกาศคณะกรรมการส่งเสริมการลงทุน ที่ 15/2565 — BOI Announcement 15/2565 (Thai, official)
  3. BOI Announcement 12/2567 — solar items and THB/MW caps (English, unofficial translation)
  4. BOI Announcement 9/2565 — list of promoted activities, 7.1.2 (English)
  5. BOI Announcement 8/2565 — Group A2 incentives (English)

Last checked against the BOI PDFs: 2026-10-05