How Long Does Factory Solar Installation Really Take?
The real timeline from contract signing to commercial operation (COD) — phase by phase, what runs in parallel, what causes delays, and whether your production line has to stop
It's the first question nearly every factory manager asks before signing: "How many months until we're actually using the power?" This page answers directly with typical ranges from CapSolar's 150+ delivered projects — plus why government paperwork usually takes longer than the physical installation, and what you can prepare in advance to move faster.
A typical factory rooftop solar project takes about 3-6 months from contract signing to commercial operation date (COD): systems under 1 MWp usually land around 3-4 months, 1-3 MWp around 4-6 months, while larger projects or those needing a transformer upgrade or EIA screening can exceed 6 months. The longest phase is usually not the installation itself but government paperwork (PEA/MEA interconnection, roughly 30-60 days), which can run in parallel with equipment procurement. Rooftop installation proceeds without stopping your production line — power is interrupted only for a short, pre-scheduled grid tie-in. All figures are typical ranges from project experience, not a guarantee.
Quick answer: how many months from signing to COD
The shortest honest answer: most projects land in the 3-6 month range. The main variables are system size, document readiness, and the local utility's inspection queue. The table below shows typical ranges by system size, from our experience delivering 150+ projects across Thailand.
| System size | Typical range (signing → COD) | Main variable |
|---|---|---|
| Under 1 MWp | ~3-4 months | PEA/MEA approval queue and document completeness — exempt from several permits |
| 1-3 MWp | ~4-6 months | Larger installation scope + utility site inspection |
| Over 3 MWp / transformer upgrade / EIA screening | 6+ months | HV electrical works, impact studies, and made-to-order equipment |
* Typical ranges from CapSolar project experience — not a guaranteed schedule. Actual timelines depend on roof condition, location, the local utility office, and each factory's document readiness.
Phase-by-phase timeline: what happens in each stage
A factory solar project moves through 6 main phases. The common misconception is that every phase queues up in a straight line — in reality phase 2 (permits) and phase 3 (procurement) can run in parallel, which is the single biggest lever for compressing the total schedule.
| Phase | What happens | Typical duration | Parallelizable? |
|---|---|---|---|
| 1. Site survey + design | Roof measurement, structural check, bill analysis, system design + single-line diagram | ~1-3 weeks | Starting point for everything |
| 2. Permits & approvals | PEA/MEA interconnection filing, Aor.6 (or Aor.1 for ground-mount), EIA/IEE screening | PEA/MEA ~30-60 days (longest phase) | ✅ Runs parallel with phase 3 |
| 3. Equipment procurement | Order panels, inverters, mounting, cabling — locked to the approved design spec | ~3-8 weeks depending on stock | ✅ Runs parallel with phase 2 |
| 4. On-site installation | Mounting structure, panel lifting, DC/AC cabling, inverter and switchboard installation | ~3-8 weeks by system size | Starts when equipment lands + structure cleared — production keeps running |
| 5. Grid connection + testing | Utility site inspection, meter installation, protection testing + commissioning | ~2-4 weeks incl. inspection queue | Strictly after phase 4 |
| 6. COD — commercial operation | System goes live into the factory, monitoring starts, savings begin immediately | Same day once cleared | — |
* Typical ranges from CapSolar project experience and the figures published in our permits guide — not a guarantee. Actual durations depend on the local utility office and each factory's document readiness.
The longest phase: government paperwork, not the build
The most common misconception is that "installing solar" means the work on the roof. In reality the roof work is usually done in a few weeks — it's the government approval process that sets the project's length: the PEA/MEA interconnection filing takes roughly 30-60 days and the building modification permit (Aor.6) roughly 30-45 days, with the full permit chain typically landing at 45-90 days. See the document-by-document detail in our factory solar permits guide.
The good news: most factories don't face the full stack. Projects under 5 MWp are mostly EIA-exempt, and self-consumption projects don't need a Ror.Ngor.4 amendment. For the full regulatory backdrop, read our Thailand rooftop solar regulations guide.
Does installation stop your production line? (Every plant manager's #1 question)
Answer: barely at all. Almost all installation work happens on the roof — mounting, panel placement, cabling — while the machines below keep running. Crews work in zones separated from production, with a safety method statement that pre-defines lifting points, exclusion areas and crane windows.
The only moment requiring a power cut is the tie-in to your main distribution board — a job of a few hours that is always scheduled in advance. Most factories pick their weekly day off, a public holiday, or a night window when the line is already resting. How well a contractor plans a painless tie-in is one of the screening questions worth asking — see how to vet a solar EPC contractor.
Bottom line: roof work runs 100% in parallel with production — the only real outage is a few-hour tie-in on a date you choose.
What slows projects down — and the checklist to speed them up
Across 150+ projects, the most frequent time-killers in order: (1) incomplete factory documents at filing — past electricity bills, building drawings, company papers — causing the application to bounce; (2) the existing transformer lacking headroom, requiring a load study or upgrade first — check this on survey day via our grid interconnection & transformer guide; (3) the local utility's inspection queue in busy periods; (4) roofs needing repair or structural reinforcement before mounting; (5) import lead time on specific equipment models.
Acceleration checklist — all preparable before you even sign: bundle 12 months of electricity bills + building drawings + company documents into one pack; have the contractor file permits the moment the design is done (don't wait for equipment); lock equipment specs to models stocked in Thailand; pre-book a tie-in date on your holiday calendar; and pick an EPC familiar with your local utility office. Projects with documents ready on day one consistently beat the midpoint of the range.
EPC vs PPA: who carries the timeline burden for you
The physical build time is nearly identical under both models — the difference is who does the running: under EPC you own the system and the contractor runs the paperwork as your agent, but the schedule risk sits with you. Under a PPA the developer owns the system and carries the entire timeline burden — permits, procurement, installation — and you pay only per unit of electricity once it flows, with one extra upfront step: a credit review of your factory before signing.
Still weighing the two models? See the detailed comparison at PPA vs EPC: which to choose — or run your own factory's numbers first with the free solar ROI calculator before talking to anyone.