Project Overview
This metal parts manufacturer operates a 3,200 m² factory roof with average monthly electricity consumption of ~25,000 kWh, predominantly from CNC cutting machines, air compressors, and factory lighting. The facility runs a day shift (07:00-17:00) that aligns directly with peak solar generation hours.
The owner contacted Sahawatthanakit (1988) through a supply-chain referral, requesting turnkey EPC (Engineering, Procurement, Construction) to avoid coordinating multiple contractors.
Scope of Work
1. Engineering — System Design
Site survey and assessment covering:
- Roof structural survey — load-bearing capacity of the 12-year-old steel roof structure, wind uplift calculation per DPT 1311
- Shading analysis — solar path diagram to identify shadow cast from exhaust vents, water tanks, and adjacent structures
- String design — 20 strings × 6 panels = 120 panels (400 Wp each = 120 kWp total), arranged to avoid partial shade bottlenecks
- Inverter sizing — two 3-phase 60 kW grid-tie inverters with independent MPPT per string
Projected output: 14,400 kWh/month (4.0 peak sun hours/day, 0.80 performance ratio)
2. Procurement — Equipment
| Equipment | Specification | Standard |
|---|---|---|
| Solar panels | 400 Wp monocrystalline PERC | IEC 61215, IEC 61730 |
| Grid-tie inverters | 60 kW × 2, 3-phase | IEC 62116 anti-islanding |
| Mounting rail system | Aluminum profile, adjustable tilt 10-15° | DPT 1311 wind load |
| AC/DC cabling | UV-resistant, fire-retardant | IEC 60227 / IEC 60245 |
| Monitoring system | Smart meter + cloud dashboard | — |
3. Construction — Installation
- Timeline: 18 working days, production line uninterrupted
- Weekend and evening shifts during critical-path work to avoid production impact
- Full commissioning and test run before grid energization
4. MEA Net Metering Connection
Full MEA paperwork handling: NEM application, metering inspection, MEA approval within 45 days of commissioning.
Challenges
Roof load constraint
No existing structural report for the 12-year-old roof. The team engaged an independent structural engineer to compute load capacity before installation, confirming the mounting system plus panels (~15 kg/m²) fell within the safe margin.
Resolution: String layout redistributed dead load evenly; lightweight aluminum rail replaced steel to reduce added weight by 30%.
Partial shading from exhaust vents
Three exhaust vents created shadow patterns between 10:00-12:00. Shading any panel in a series string creates a bottleneck that degrades the entire string's output.
Resolution: Shadow-zone panels placed on separate strings; inverters selected with per-string independent MPPT to isolate the performance impact.
Outcomes
| Metric | Result |
|---|---|
| Installed capacity | 120 kWp |
| Actual output (months 1-3) | 13,800-14,600 kWh/month |
| Electricity cost reduction | 58% vs. baseline |
| Payback period | 5.4 years |
| Grid export (month 1) | 1,200 kWh |
| CO₂ reduction | ~7.8 tonnes/month |
| Installation duration | 18 working days |
Why the Factory Chose Us
- Zero production downtime — scheduling expertise to work around the live production shift
- Single-contractor EPC — one point of contact for engineering, installation, and MEA paperwork
- Itemized transparent pricing — detailed BOM + labor breakdown before contract signing
- After-sales monitoring — daily generation dashboard with alert thresholds
Related Services
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