BOI Solar Thailand 2026: What Changed
Since 1 July 2025 (BOI Announcement 3/2568), BOI no longer promotes installing solar power systems under the alternative-energy efficiency measure — the route factories used for rooftop solar. This page covers what changed, who keeps the old terms, which routes remain, and real payback without BOI.
This page summarises published Board of Investment announcements (the Thai text is the official version). It is not legal or tax advice. BOI decides each application — check the latest announcement on boi.go.th and ask BOI before planning around any incentive.
Can a factory still get BOI for rooftop solar?
No — not for solar a factory installs for its own use and applies for from 1 July 2025. BOI Announcement 3/2568 stopped promotion for "installing solar power generation systems" under the alternative-energy efficiency measure (it used to give machinery import-duty exemption plus a 3-year CIT exemption capped at 50% of the investment). Companies whose business is selling solar electricity (≥200 kW per distribution point, activity 7.1.2) remain in Group A2: an 8-year CIT exemption capped at 100% of investment. For a factory, base the decision on bill savings alone — about 3.7–4.0 years simple payback in the 500 kW–5 MW examples below.
1. Timeline: from 15/2565 to 3/2568
Every row links to the BOI announcement itself (PDF). The Thai text is official; English versions are unofficial translations.
| Date | Announcement | What it does |
|---|---|---|
| BOI Announcement 15/2565 | Smart and Sustainable Industry measure · §1.4 efficiency improvement for alternative-energy use — the route factories used for self-use solar: machinery import-duty exemption + 3-year CIT exemption on the existing business's income, capped at 50% of the investment (excluding land and working capital). In force from 3 Jan 2023. | |
| BOI Announcement 12/2567 | Lists the solar items that count (modules, inverters, transformers, distribution/control/monitoring/security/weather-station/cleaning systems, BESS and BESS inverters, installation and mounting) and caps the investment counted for the CIT exemption at THB 30M per MW (THB 40M per MW with BESS). Applies to applications filed from 1 Nov 2024. | |
| BOI Announcement 3/2568 | Clause 1: stops investment promotion for installing solar power generation systems under the alternative-energy efficiency measure. Clause 2: §1.4(2) now reads "excluding installation of solar power generation systems". Clause 3: BESS and BESS inverters count for the CIT cap at no more than THB 12M per MW. | |
| 3/2568 clause 4 | 3/2568 applies to applications filed from this date → self-use solar can no longer be promoted under this measure. Solar applications filed 5–30 June 2025 are not allowed extensions of the deadlines to accept the promotion resolution and to submit evidence for certificate issuance. |
2. What the old self-use route gave (15/2565 §1.4)
The measure applied to businesses already operating, promoted or not (an existing BOI project could apply once its CIT incentive had ended), with an improvement investment of at least THB 1M (excluding land and working capital). Benefits: machinery import-duty exemption and a 3-year CIT exemption capped at 50% of the investment, exempting income of the existing business — not 8 years, and not 100%. The exemption period counted from the first income after the certificate, and the project had to be completed within 3 years of the certificate date. The real value therefore depended on the existing business's profit in those 3 years. Land & building tax is a separate matter — see land and building tax for factory solar; T-VER carbon-credit revenue has nothing to do with BOI.
3. Filed before 1 July 2025 — what now?
3/2568 applies to applications filed from 1 July 2025. Earlier applications are handled under the rules in force when filed (filed from 1 Nov 2024: the THB 30M/MW cap of 12/2567). Key exception: solar applications filed 5–30 June 2025 are not allowed extensions of the deadlines to accept the promotion resolution and to submit evidence for certificate issuance. If you already hold a certificate, check its conditions — especially completion within 3 years of the certificate date — and keep income and investment records complete for claiming the exemption.
4. BOI routes that may still apply
Status of each route per the announcements. Where it says UNKNOWN, we have not seen the original text — do not plan an investment around it.
| Route | Status | Benefit | Source |
|---|---|---|---|
| Factory self-use solar · filed from 1 Jul 2025 | Closed | No BOI benefit for the solar installation | 3/2568 cl. 1, 2, 4 |
| Self-use solar · filed by 30 Jun 2025 | Rules in force when filed · 5–30 Jun 2025 filers get no extensions | Machinery import-duty exemption + 3-yr CIT exemption on existing-business income, ≤50% of investment (filed from 1 Nov 2024: counted investment ≤ THB 30M/MW) | 15/2565 §1.4 · 12/2567 · 3/2568 cl. 4 |
| Battery energy storage (BESS) | New cap set · project eligibility per BOI criteria | BESS + BESS inverter counted for the CIT exemption at ≤ THB 12M per MW | 3/2568 cl. 3 |
| Selling solar electricity (activity 7.1.2) | Still Group A2 · solar must be ≥200 kW per distribution point | 8-yr CIT exemption ≤100% of investment + machinery import-duty exemption — a power-producer benefit (e.g. a PPA developer), not a self-use one | 9/2565 (7.1.2) · 8/2565 (Group A2) |
| SME measure (Announcement 5/2568) | UNKNOWN | Not confirmed whether rooftop solar qualifies — ask BOI before planning around it | Confirm with BOI |
5. Real payback without BOI
CAPEX and annual generation come from the 5-size table on factory solar ROI; each kWh saved is valued at THB 3.86/kWh (all-class average, ex-VAT, Sep–Dec 2026). Year-1 simple payback, assuming all output is used on site and before O&M (with O&M and 85–92% self-consumption see the worked example without BOI). BOI benefit for self-use applications filed from 1 Jul 2025 = 0.
| System size | CAPEX | Generation / yr | Bill savings / yr | Payback (yr) | BOI benefit (filed from 1 Jul 2025) |
|---|---|---|---|---|---|
| 500 kW | ฿11.5M | 745k kWh | ฿2.9M | 4.0 | ฿0 |
| 2 MW | ฿44.0M | 2.98M kWh | ฿11.5M | 3.8 | ฿0 |
| 5 MW | ฿107.5M | 7.45M kWh | ฿28.8M | 3.7 | ฿0 |
For applications filed by 30 Jun 2025 only: the CIT exemption ceiling was 50% of the counted investment — e.g. for the 2 MW case (CAPEX THB 44M) the ceiling is THB 22M, but the benefit actually received equals the existing business's tax in the 3 exempt years, up to that ceiling. Lower-voltage tariffs or On-Peak displacement raise the value per kWh and shorten payback — see the sensitivity table on the ROI page.
6. 5 steps to check a factory solar project's BOI position
Run this before signing an EPC or PPA contract.
Step 1 · Decide: self-use or selling electricity
A factory installing solar to cut its own bill used Announcement 15/2565 §1.4. A business generating solar power for sale (≥200 kW per distribution point) falls under activity 7.1.2, Group A2 — a different activity.
Step 2 · Check the filing date
Filed from 1 Jul 2025: self-use solar is no longer promoted (3/2568). Filed by 30 Jun 2025: the rules in force on the filing date apply. Filed 5–30 Jun 2025: no extensions to accept the resolution or submit certificate evidence.
Step 3 · If you hold a certificate, check its deadlines
Under §1.4 the exemption period counts from the date income arises after the certificate, and the project must be completed within 3 years of the certificate date. Your certificate's own conditions govern.
Step 4 · Model the project without BOI
For a new project, base the payback on bill savings only — see the table below, factory solar ROI and the solar calculator.
Step 5 · Confirm with BOI before committing
Read the latest announcements on boi.go.th and ask BOI directly — especially for BESS and the SME measure (5/2568), which are decided project by project.
7. EPC vs PPA after the change
EPC (self-investment): the factory owns the system and keeps all bill savings, but new applications get no BOI benefit. PPA: a developer owns the system and sells power to the factory — if the developer meets activity 7.1.2 (≥200 kW per distribution point), the A2 benefit belongs to the developer; whether any of it shows up in the PPA price is a commercial negotiation, not something BOI sets. Compare both in EPC vs PPA and what is a PPA.
Related articles
Solar guides by industry
Your main-activity BOI status (if any) is separate from solar — these guides size the case from each industry's load profile.
Frequently Asked Questions
Sources (BOI announcements)
- ประกาศคณะกรรมการส่งเสริมการลงทุน ที่ 3/2568 (5 มิ.ย. 2568) — BOI Announcement 3/2568 (Thai, official)
- ประกาศคณะกรรมการส่งเสริมการลงทุน ที่ 15/2565 — BOI Announcement 15/2565, Smart and Sustainable Industry (Thai, official)
- BOI Announcement 15/2565 (English, unofficial translation)
- BOI Announcement 12/2567 — solar items and THB/MW caps (English, unofficial translation)
- BOI Announcement 9/2565 — list of promoted activities, 7.1.2 (English)
- BOI Announcement 8/2565 — policies and criteria, Group A2 incentives (English)
Last checked against the original PDFs: 2026-10-05