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.
The rooftop solar regulations in Thailand are governed mainly by capacity tier. In short: a commercial system under 1 MW used for self-consumption needs no ERC license and — since the late-2024 Factory Act amendment — no longer requires 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 of the rooftop solar regulations in Thailand and links down to its full guide.
The framework for rooftop solar regulations in Thailand in 2026 is relatively settled and more investment-friendly than a few years ago. Here are the five points that are current for this year — each anchored to a rule in force, and each to be confirmed against the latest ERC, PEA/MEA, or Revenue Department guidance before you commit:
1. Licensing is still capacity-tiered (unchanged): a self-consumption system under 1 MW remains exempt from an ERC generation licence, 1–10 MW falls under VSPP, and above 10 MW becomes SPP/IPP — this tier structure is still the operative framework in 2026.
2. The รง.4 relief still stands in 2026: since the late-2024 Factory Act amendment, installing rooftop solar for self-consumption is no longer a change in factory activity type, so no รง.4 amendment is needed — except where you export meaningful power or run a Direct PPA.
3. Surplus-power handling — net-metering stays limited: for commercial factories, true 1:1 net-metering is open only to certain tariff classes / smaller users as PEA/MEA allow; most sites run net-billing (surplus bought back below retail) or zero-export. So in 2026, designing for maximum self-consumption is still the most economic strategy — confirm the available scheme with PEA/MEA for your meter class.
4. Tax incentives are widening: Royal Decree #805 gives a 1.5× deduction of solar equipment cost against corporate income tax (stackable with BOI Section 7.1), and 2026 adds a personal income-tax deduction of up to THB 200,000 for residential rooftop solar (qualifying spend 3 Mar 2026 – 31 Dec 2028) — detail and conditions to be confirmed with the Revenue Department.
5. Direct PPA is taking shape: 2026 carries an ERC Direct PPA pilot of around 2,000 MW that lets power be sold directly between users across the grid (wheeling charge ~1.07 THB/kWh) — a new channel for factories wanting green power or off-site investment. It remains a pilot, so track the latest ERC announcements.
Bottom line for 2026: for a typical factory installing under 1 MW for self-consumption, the permitting path is now much simpler — no ERC licence, no รง.4 amendment, leaving just PEA/MEA interconnection plus a building permit, alongside better tax incentives. The table and sections below go deeper on each area with links to the in-depth guides.
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.
For a typical factory installing rooftop solar under 1 MW for self-consumption, the 2026 compliance path has four main steps: (1) confirm your capacity tier to know whether an ERC license applies; (2) obtain the อ.6 building-modification permit from the local authority; (3) file the grid-interconnection application with PEA or MEA; and (4) choose how you handle surplus power (net-billing / zero-export) and claim any tax incentives. A self-consumption system under 1 MW needs no ERC license and no รง.4 amendment. End-to-end this usually takes around 60–120 days (confirm with the relevant authority).
Check your installed capacity: under 1 MW self-consumption is exempt from a license, 1–10 MW is VSPP, and above 10 MW is SPP/IPP. See the full thresholds in Thailand solar law & licensing.
Apply for the อ.6 permit from the local building authority, with drawings signed by a licensed civil engineer. See the documents and timeline in the PEA/MEA permit & approvals guide.
File with PEA (outside Bangkok) or MEA (Bangkok / Nonthaburi / Samut Prakan) — the wrong utility resets the clock; systems ≥1 MWp or ≥69 kV also coordinate with EGAT. See the process in the PEA/MEA permit & interconnection guide.
Choose how to handle surplus power — net-billing or zero-export (compared in net billing vs net metering) — and claim the 1.5×/BOI incentives (see BOI solar 2026).
Note: this is a high-level path for a typical self-consumption system. Meaningful export, a Direct PPA, or larger systems add further steps. The actual detail and timelines 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. Beyond that corporate benefit, RD-805 also lets an individual homeowner claim a personal income-tax deduction for the actual cost (VAT included) of buying and installing an on-grid residential rooftop solar system, capped at THB 200,000, for qualifying spending from 3 March 2026 through 31 December 2028. The system must be grid-connected (MEA/PEA approved), the claimant must be the electricity-meter owner with a valid e-Tax Invoice from a VAT-registered installer, and only one system per household may be claimed, once. (Widely reported additional conditions include a capacity of up to ~10 kWp and a residential Type-1 meter — confirm with the Revenue Department.) This residential deduction is separate from the corporate 1.5× deduction above; see the residential context in Thailand net-metering.
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. Want to know how many kW your roof supports? Try the roof area estimator.
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: Jul 2026
The CapSolar team helps you plan permitting, grid interconnection, and tax-incentive claims end-to-end — free consultation.