Before you drill into any one process, here is the lay of the land: every regulatory area for commercial rooftop solar in Thailand in one place — who regulates it, whether you need a license or รง.4, how you connect to the grid, whether you can export power, and what tax incentives apply — each linking down to its in-depth guide.
Commercial rooftop solar in Thailand is governed mainly by capacity tier. Systems under 1 MW for self-consumption need no ERC license and — since the late-2024 Factory Act amendment — no longer require a รง.4 amendment, leaving only a PEA or MEA grid-interconnection approval and a building-modification permit. Larger systems, grid export, or a Direct PPA add further licensing. This page summarises each area and links down to its full guide.
The main authorities involved in Thai rooftop solar, what each governs, when it applies, and a link to the in-depth guide for each area:
| Regulator | What it governs | When it applies | Deep guide |
|---|---|---|---|
| ERC (กกพ.) | Generation licensing by capacity tier (<1 MW exempt, 1–10 MW VSPP, >10 MW SPP/IPP) | Every project (sets oversight level) | Thailand solar law & licensing |
| PEA / MEA | Grid interconnection + net-metering / net-billing | Every on-grid system (PEA outside Bangkok, MEA in Bangkok / Nonthaburi / Samut Prakan) | PEA/MEA permit & interconnection guide |
| DIW | รง.4 — after the new Factory Act, no รง.4 amendment for self-consumption | Only if exporting meaningful power / Direct PPA | Thailand solar law & licensing |
| EGAT | High-voltage interconnection coordination (≥69 kV) | Projects ≥1 MWp or ≥69 kV | grid interconnection & transformer |
| Local building authority | Building modification permit อ.1 / อ.6 | Roof / structural mounting | PEA/MEA permit & approvals guide |
| ONEP | EIA / IEE (environmental assessment) | EIA ≥10 MWp, IEE 5–10 MWp (most rooftop projects exempt) | PEA/MEA permit & approvals guide |
| BOI + Revenue Dept | Tax incentives (RD #805 1.5× deduction; BOI Section 7.1) | When claiming incentives | BOI solar incentives 2026 |
Note: this table is a high-level overview. The actual detail, thresholds and timelines for each area are in the linked in-depth guides, and should always be confirmed with the relevant authority.
The ERC regulates power generation by capacity tier: self-consumption systems under 1 MW are generally exempt from licensing, 1–10 MW fall under a VSPP license, and above 10 MW become SPP/IPP. Read the full thresholds in our Thailand solar law & licensing framework.
Since the late-2024 Factory Act amendment, installing rooftop solar for self-consumption is no longer treated as a change in factory activity type — so no รง.4 amendment is needed. However, if the system exports meaningful power or serves a Direct PPA, a รง.4 activity-category amendment with DIW may still apply. See the overview in our Thailand solar law guide and the process detail in the PEA/MEA permit guide.
Every on-grid system must apply to PEA (outside Bangkok) or MEA (Bangkok, Nonthaburi, Samut Prakan) — submitting to the wrong utility resets the clock. Systems ≥1 MWp or connecting at ≥69 kV must also coordinate with EGAT. See the full process in the PEA/MEA permit & interconnection guide and transformer compatibility in the grid interconnection & transformer guide.
Every grid-tied inverter must carry anti-islanding certification (UL 1741 or IEEE 1547) and trip within 2 seconds of grid loss, per the ERC Grid Code B.E. 2559. Read the requirement detail in the anti-islanding section of the permit guide.
There are several ways to handle surplus power: net-metering (1:1 monthly energy offset, open to small users under 1 MWp where available for your tariff class — confirm with PEA/MEA), net-billing (selling surplus at a buyback rate below retail), and zero-export, which prohibits any backfeed to the grid. Compare them all in net billing vs net metering, see the net-metering rules in Thailand net-metering, and the zero-export requirements in the zero-export guide.
Most factory solar systems are designed for self-consumption with minimal export. Factories that do not apply for export approval must comply with zero-export / no-backfeed rules, fitting an anti-backfeed device that prevents power flowing back to the grid. Read the compliance approach and equipment in the zero-export / no-backfeed guide.
Rooftop installations on an existing building usually need a building-modification permit อ.6 (or อ.1 for a new structure), with drawings signed by a licensed civil engineer. For environmental review, an EIA is required at ≥10 MWp and an IEE for 5–10 MWp — so the vast majority of rooftop projects (hundreds of kWp to a few MWp) are exempt. See the documents and timelines in the PEA/MEA permit & approvals guide.
Royal Decree #805 allows a 1.5× deduction of solar equipment cost against corporate income tax, and it can stack with BOI Section 7.1 (8-year CIT exemption + 0% import duty). Read how to apply and calculate in BOI solar incentives 2026, and the tax overview in our Thailand solar law guide.
There are two distinct ways to sell power: a utility PPA sells your surplus back to PEA/MEA, while a Direct PPA sells electricity directly to another consumer over the PEA/MEA/EGAT grid (wheeling charge ~1.07 THB/kWh), with a 2026 ERC Direct PPA pilot of around 2,000 MW. Read the buyer's angle in the Direct PPA factory guide and the green-procurement option in Utility Green Tariff UGT2.
CapSolar handles the entire chain end-to-end — PEA/MEA interconnection, the อ.6 building permit, รง.4 (where needed), the BOI application, through to COD and net-metering — included in the EPC/PPA scope with no separate fee. Start with our factory solar service or run a quick system estimate.
This article is prepared by Frank Lee, Founder of CapSolar, which has delivered 80+ MWp of commercial & industrial solar across 150+ projects for 100+ clients. We help factories navigate the full permitting and grid-connection process end-to-end.
Reviewed by: CapSolar Engineering Team | Updated: Jun 2026
The CapSolar team helps you plan permitting, grid interconnection, and tax-incentive claims end-to-end — free consultation.