Factory Solar ROI in Thailand 5 Real Sizes · 4.0-4.8 year payback
Model your factory solar return seriously — payback, IRR, NPV, LCOE across 5 real sizes (100kW, 500kW, 1MW, 2MW, 5MW), shift-based load profiles competitors never cover, BOI tax-holiday impact, and real Thai bank green-loan rates.
How Factory Solar ROI Differs from Residential
Thailand factory solar ROI in 2026 averages 4.0-4.8-year payback — much faster than residential (6-8 years) because factories consume ~100% of generation during daylight (high self-consumption), don't depend on net metering, qualify for 8-year BOI tax holidays (unavailable to residential), and benefit from economies of scale (EPC per-watt drops 15-20% at 1 MW+). Key variables that swing ROI: shift profile (load curve), BOI section tier, existing roof structural cost, tariff escalation rate.
3 ROI Mistakes Factory CFOs Routinely Make
1) Computing "electricity cost saved" from flat average tariff — ignoring that daytime-running factories pay peak-hour rates ~40% higher than off-peak. Solar displaces peak directly, so ROI is 15-20% higher than a flat-rate model suggests. 2) Forgetting tariff escalation — ERC has raised tariffs 3-4% annually for the past decade, but CFOs often lock in the investment-year rate, under-estimating 25-year NPV by ~25%. 3) Missing BOI Section 30/31 — the 8-year tax holiday + VAT exemption drops effective CAPEX from THB 22-26/Wp to THB 18-22/Wp, cutting payback by an average 1.5 years. This guide corrects all three with real numbers.
The 7 Variables of Factory Solar ROI
Accurate solar ROI requires plugging all 7 variables below into a 25-year cash-flow model (not a single-year simple payback). The seven are: CapEx, OpEx, tariff structure, tariff escalation, discount rate, degradation, O&M & insurance.
1. CAPEX (Upfront Investment)
THB 22-26/Wp installed (2026) for 100kW-500kW, THB 21.5-23/Wp for 1MW+. Covers panels, inverter, BOS, labor, commissioning. Excludes new roof structural work. BOI reduces this by ~15% (details at /knowledge/boi-solar-incentives-2026).
2. Tariff Savings (revenue)
ERC 2026: THB 3.88-3.95/kWh average (industrial TOU Cat 3-4) × PVOUT 1,490 kWh/kWp × installed kW = first-year savings. Warning: don't use a flat tariff if the factory runs during peak — use actual peak rate.
3. Tariff Escalation Rate
ERC 10-year historical: ~3.2%/yr. Use 3% in base case, 4% aggressive, 2% conservative — the spread shifts NPV by ~35%.
4. Degradation Rate
Tier-1 mono panel: year-1 drop 2.5%, then 0.5%/yr. 25-year warranty: >83% of original rated power. Model must use this curve, not flat.
5. O&M + Insurance
THB 150-200k/MW/year — covers 4x cleaning, inspections, remote monitoring, all-risk insurance. About 1-1.5% of CAPEX annually; an OpEx line many CFOs forget.
6. Discount Rate (WACC)
Use factory's WACC (typically 7-10% for Thai SME, 5-8% for BOI-backed corporates). Lower WACC → higher NPV → more attractive investment.
7. BOI Tax Impact
Sections 30/31 grant an 8-year corporate tax holiday + 7% import VAT exemption. Net impact: 2-3 percentage points higher 25-year ROI. See /knowledge/boi-solar-incentives-2026.
5 Real Factory Sizes — Worked Payback / IRR / NPV
We model 5 sizes common in Thai industry — 100 kW (SME), 500 kW (mid-market), 1 MW (mainstream), 2 MW (major), 5 MW (utility-scale). All numbers use ERC 2026 tariff, PVOUT 1,490, WACC 8%, tariff escalation 3%/yr, BOI Section 30 (8-year tax holiday). This table is the golden benchmark.
| Size | CAPEX (after BOI) | Year-1 savings | Payback | 25-yr IRR | 25-yr NPV (@ 8%) | LCOE |
|---|---|---|---|---|---|---|
| 100 kW | ฿2.04M | ฿580K | 4.8 yr | 19.2% | ฿4.10M | 1.32THB/kWh |
| 500 kW | ฿9.78M | ฿2.90M | 4.5 yr | 20.8% | ฿22.00M | 1.28THB/kWh |
| 1 MW | ฿19.55M | ฿5.82M | 4.3 yr | 21.7% | ฿46.50M | 1.24THB/kWh |
| 2 MW | ฿37.40M | ฿11.45M | 4.1 yr | 22.4% | ฿98.00M | 1.22THB/kWh |
| 5 MW | ฿91.38M | ฿28.70M | 4.0 yr | 22.9% | ฿250.00M | 1.20THB/kWh |
1 MW
- Roof area
- 6,800 sqm
- Annual generation
- 1,490,000 kWh/yr
- CAPEX (after BOI)
- ฿19.55M
- 25-year IRR
- 21.7%
- 25-year NPV (@ 8%)
- ฿46.50M
- LCOE
- 1.24 THB/kWh
- Shift profile (illustrative)
- Continuous 3-shift 24h · daytime load 1,100 kW fully absorbs generation peak
- Analysis
- 1 MW is a key threshold — EPC price-per-watt drops ~10% vs 500 kW due to economies of scale. 3-shift factories consuming 250,000+ kWh/month absorb all generation during daylight — no grid export needed, maximizing IRR (21.7% over 25 years). Full price BOM at /knowledge/factory-solar-1mw-price-thailand.
Shift-Based ROI Adjustments — 24/7 vs 3-shift vs 2-shift (What Competitors Miss)
Competitors like GreenYellow and Thai Solar Energy model ROI assuming a factory absorbs 100% of solar generation — which isn't true. A factory's load curve dictates its self-consumption rate, and self-consumption rate drives real ROI. Three profiles we see in the field:
A) Continuous 24/7 (cold-storage, semiconductor, data center, petrochemical)
Baseline load 4-10 MW around the clock · 1-5 MW solar is absorbed at 100% instantly · self-consumption = 100% · zero curtailment, no net-metering dependency · highest IRR (22-23%). ROI is 15-20% above what competitors quote because there's no grid-export discount to model.
B) 3-shift 24h weekdays (electronics, auto-parts 3-shift, large textile)
3-shift Mon-Fri, weekend load drops 30-50% · Sunday afternoon solar can exceed peak load → ~3-5% export · self-consumption 95-97%. ROI remains high but the model must correctly discount exports (PEA buys excess at ~THB 2.2/kWh, below tariff).
C) 2-shift 08:00-22:00 (food-processing, SME, fab shop)
Daytime load aligns well with solar profile, but tail hours 16:00-18:00 see solar drop ≤60%. Peak-hour load (11:00-15:00) at high TOU rates is fully displaced — maximum benefit. ROI optimal at 100-500 kW where solar doesn't exceed daytime baseline. Rule of thumb: size solar ≤1.2× of daytime peak load to keep self-consumption >95%.
Takeaway: size solar to shift profile, not maximum roof area. Self-consumption rate 95%+ is the ROI sweet spot. If roof exceeds load capacity, consider partial PPA export or reserve area for a phase-2 expansion.
Calculate Your Factory's ROI — 5 Minutes
The examples above use industry averages — yours may differ (actual TOU peak rate, real load curve, roof tilt/orientation affecting PVOUT). Use /tools/solar-calculator with 5 inputs (monthly kWh, average tariff, roof area, province, usage type) to get your 25-year ROI in under 30 seconds. Or book a full site assessment (free).
3 Financing Options — Cash / Loan / PPA
ROI shifts with financing structure. CFOs should benchmark 3 models:
| Option | Rate / Cost | Payback | IRR | Best for |
|---|---|---|---|---|
| Cash | 0% (own cost of capital) | 4.0-4.8 yr | 21-23% 25-yr | Best for: companies with cash reserves + low WACC + wanting asset ownership |
| Green Loan (Krungsri/EXIM/KBank) | 5.5-7% APR · 7-10-yr term | net-positive cash flow year 1-2 | 16-19% 25-yr (equity) | Best for: SME / mid-market with credit wanting to preserve cash for expansion |
| PPA (power purchase) | 0 CAPEX · THB 3.30-3.50/kWh × 15-20 yr | immediate savings | N/A (non-owner) · 10-15% below tariff | Best for: zero-CAPEX preference, cash-conservative, or leased rooftop |
Full 3-model comparison at /knowledge/ppa-vs-epc and /knowledge/solar-epc-vs-rental-thailand
BOI Section 30/31 — Cuts Payback by 1.5 Years on Average
Thailand Board of Investment (BOI) is the government agency granting tax privileges for renewable-energy projects. Section 30 provides 5-8 year tax holidays; Section 31 grants 8-year corporate income tax exemption + 7% VAT exemption on equipment imports. ROI impact: 1) CAPEX drops ~15% on average (THB 22-26/Wp → THB 18-22/Wp); 2) the 8-year tax holiday lifts after-tax cash flow ~20% during the payback window; 3) combined, average payback falls from 5.5-6 years → 4.0-4.5 years, and 25-year IRR rises from 18-19% → 21-23%. Requirements: BOI application (2-4 months), minimum investment THB 1M, and at least 30% local content (labor + installation). Full details at /knowledge/boi-solar-incentives-2026 (W3 Tue).
4 Risks to Model Explicitly
1) Grid interconnection with PEA/MEA: >1 MW requires transformer capacity review (6-9 month buffer). 2) PEA quota: some provinces have quotas (parts of EEC) — wait-list risk. 3) Tariff cap risk: ERC may revise feed-in tariff (policy under review). 4) Roof asset risk: roofs with <10-year remaining life may need replacement, adding 10-15% to CAPEX. Include sensitivity analysis for all 4 in base/upside/downside cases.
How to Calculate Your Factory Solar ROI — 5 Steps
Use these steps in-house with your finance team, alongside /tools/solar-calculator.
- 1
1) Pull 12-month electricity bills
Request 12 months of PEA/MEA bills. Record monthly kWh, TOU peak/off-peak rates, demand charge, Ft — establishing baseline.
- 2
2) Measure daytime load
Install a smart meter or request interval data from PEA. Review the 09:00-17:00 load curve. Size solar ≤ daytime peak × 1.2.
- 3
3) Get 3 EPC quotes
Request quotes from BOI-certified EPCs with 100+ installations + trilingual team. Compare THB/Wp, warranty, timeline. Recommended shortlist at /knowledge/thai-factory-solar-vendors.
- 4
4) Build 25-year cash flow model
Excel or use /tools/solar-calculator. Plug in the 7 variables (CAPEX, savings, escalation, degradation, O&M, discount, BOI). Compute payback, IRR, NPV.
- 5
5) Run sensitivity analysis
Create base/upside/downside cases — flex tariff escalation ±1%, CAPEX ±10%, degradation ±0.5%/yr. Obtain an IRR/payback range. CFO should see the range before signing.
Frequently Asked Questions
Written by Frank Lin · CEO, CapSolar
Frank Lin is the CEO and founder of CapSolar, a BOI-certified solar EPC firm (founded 2023) serving factories across Thailand. Frank manages a 16.5 MWp portfolio across 8 commercial projects in Bangkok / EEC / northern provinces. This guide was reviewed by CapSolar's Chief Engineer for engineering and financial accuracy.
Published 2026-04-23 · Last updated 2026-04-23
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