Does a factory still need a รง.4 licence for solar?
The current answer under Ministerial Regulation No. 3 B.E. 2567 (Royal Gazette 27 Dec 2024) — with a new-vs-old comparison and what you must still do after the exemption.
Since 27 December 2024, a factory installing solar on its roof no longer needs a รง.4 factory operating licence — including systems above 1 MW. Ministerial Regulation Re: Designation of Type, Kind, and Size of Factories (No. 3) B.E. 2567 removed rooftop solar from the legal definition of a “factory” regardless of generating capacity. But this exemption does not mean zero paperwork — you must still (1) file an exemption notification or apply for an energy-business licence with the ERC depending on system size, (2) obtain a building-modification permit, and (3) get grid-interconnection approval from PEA or MEA. See the full factory-solar permit steps and the Thailand solar law framework 2026.
New rules vs old rules — what changed at the end of 2024?
Before late 2024, a factory installing solar above 1 MW had to obtain or amend its รง.4 factory licence to add the power-generation activity — a slow, paperwork-heavy step, so some developers deliberately capped systems at 999 kW to avoid it. Ministerial Regulation No. 3 B.E. 2567 removed the capacity condition entirely.
| Aspect | Before 28 Dec 2024 | From 28 Dec 2024 |
|---|---|---|
| System ≤ 1 MW (self-use) | Generally no รง.4 | No รง.4 |
| System > 1 MW on rooftop | รง.4 required / amended | No รง.4 (capacity cap removed) |
| “Factory” definition | Solar > 1 MW counted as a power factory | Rooftop solar not a factory |
| Inside IEAT industrial estate | Per IEAT rules + old รง.4 | Still need IEAT land-use permit (01/2) + business notification |
Note: the รง.4 exemption applies mainly to roof/building-mounted solar outside industrial estates. Projects inside an IEAT estate must still follow the IEAT's own land-use and notification rules.
รง.4 is gone — but three steps still apply
Removing รง.4 eliminates the single biggest hurdle, but legally installing factory solar still means clearing three authorities:
1. ERC (กกพ.) — exemption notice or licence
By system size: small systems (typically under 1,000 kVA) file an online “notification of exemption from being an energy business operator” — simple and fast. Larger systems (1,000 kVA and above) must apply for an energy-business licence. When connecting to the grid, the utility usually forwards the case to the ERC for you. (Confirm the current kVA threshold with the ERC, as it can be revised.)
2. Building modification permit (อ.1 / อ.6)
Mounting panels on a roof is generally treated as a building modification under the Building Control Act, so an อ.1/อ.6 permit from the local authority is usually required. A May 2025 cabinet decision moves to exempt light rooftop systems (roughly ≤20 kg/m² and ≤160 m²) from counting as a modification, but the implementing ministerial regulation is still pending — confirm the latest status with your local authority or EPC contractor.
3. Grid interconnection with PEA / MEA
Every grid-parallel system needs an interconnection approval from the Metropolitan Electricity Authority (MEA — Bangkok, Nonthaburi, Samut Prakan) or the Provincial Electricity Authority (PEA — elsewhere), submitting a single-line diagram and anti-islanding protection. If you do not export power, a reverse-power-protection device is required — see the Zero Export guide for factory solar.
This is a general summary as of June 2026, not case-specific legal advice. Thresholds and procedures can differ by locality and project size — confirm with the ERC / your utility / your local authority, or have your EPC contractor handle it.
By capacity and scenario
| Scenario | รง.4 | What you do |
|---|---|---|
| Rooftop ≤ 1 MW, outside estate | Not needed | ERC exemption notice (online) + อ.1/อ.6 + PEA/MEA interconnection |
| Rooftop > 1 MW, outside estate | Not needed | ERC energy-business licence + อ.1/อ.6 + interconnection |
| Inside IEAT industrial estate | Not needed* | IEAT land-use permit 01/2 + business notification + ERC/interconnection steps |
| Ground-mounted solar | May still apply | The exemption targets roof/building-mounted systems; large ground-mount should be checked case-by-case |
* The รง.4 exemption covers roof/building-mounted solar of any size, but projects inside an IEAT estate must still clear the IEAT's own rules.
CapSolar handles the ERC filing, the building permit and the PEA/MEA interconnection end-to-end for every EPC and PPA client — backed by 80+ MWp installed across 150+ projects in Thailand. See the full factory solar guide or BOI solar incentives 2026.
Author
Compiled by the CapSolar team, led by Frank Lee (Founder), specialists in factory-scale solar EPC and PPA in Thailand. Based on Ministerial Regulation No. 3 B.E. 2567 and current ERC / utility practice. Last reviewed June 2026.
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