Industrial rooftop solar design begins long before PV modules touch the site. For EPC contractors and electrical engineers, the site survey is the single most important determinant of technical accuracy, BOQ precision, and downstream project safety. In West Bengal—where aging industrial structures, mixed roofing profiles, and variable grid reliability are common—the survey stage must be methodical, instrument-driven, and thoroughly documented.
This guide provides a structured, engineer-friendly survey workflow aligned with current Indian practices, including CEIG norms and state DISCOM requirements. All steps reflect Vedic Solar’s on-ground process for commercial and industrial (C&I) rooftop projects.
1. Pre-Survey Preparation
1.1 Collect baseline data
Obtain from the client:
- Connected load (kVA) and sanctioned load documents
- Monthly consumption (kWh) for 12 months
- DG set ratings & interlock arrangement
- Existing SLD, if available
- Roof access constraints, operating hours, and safety restrictions
This saves 30–40% time during the site visit and ensures you reach prepared with the right instruments.
1.2 Tools checklist
Essential survey tools include:
- Digital laser distance meter
- Clamp meter (AC/DC)
- IR thermometer
- Roof measuring tape
- Compass or smartphone azimuth app
- Drone (optional but increasingly standard)
- Lux meter for indoor inverter room evaluation
- Moisture meter (for RCC roofs)
For sites in coastal West Bengal, where corrosion risk is high, adding a coating-thickness gauge and surface-condition checks prevents fragile structures from being overstressed.
2. Structural Assessment of Rooftop
2.1 Roof type identification
Industrial rooftops typically fall into:
- Metal sheet roofs (trapezoidal, standing seam, KLIP-LOK)
- RCC flat roofs
- Asbestos or old fibre roofs (usually rejected for PV installations)
The surveyor must document:
- Sheet gauge
- Purlin spacing
- Corrosion zones
- Load-bearing history (AHUs, ducts, tanks)
- Thermal movement patterns on long spans
For RCC roofs, record:
- Slab thickness
- Column–beam grid
- Parapet wall condition
- Cracks or deflection signs
Vedic Solar’s rule of thumb for West Bengal’s industrial zones: if the purlin spacing exceeds 1.4 m or the sheet gauge is weaker than 0.5 mm, structural reinforcement or ballasted solutions may be needed.
3. Roof Dimensions and Usable Area Mapping
Accurate dimensioning impacts module layout efficiency, cable routing, and BOS cost.
3.1 Measure:
- Roof length, width
- North–south slope direction
- Height above ground level
- Obstructions (vents, skylights, chimneys, cranes)
- Safe walkways
3.2 Usable area
After deducting clearances:
- 0.6–1.0 m maintenance aisles
- Safety line corridors
- Shadow-affected strips
- Weak zones
Most C&I roofs yield 65–75% usable area; well-planned factories can exceed 80%.
A roof sketch (manual or digital) must be included in the survey report with obstruction coordinates.
4. Electrical Assessment
4.1 LT Panel & Feeder Mapping
Record:
- Main Incoming Panel configuration
- Available breaker ratings
- Spare ACB/MCCB slots
- Maximum demand reading trends
- Earthing grid layout
- DG synchronization and relay settings
Grid reliability in West Bengal varies by industrial cluster, so system design must anticipate voltage fluctuations and flicker during daytime peaks.
4.2 Inverter Room Feasibility
Check:
- Room ventilation (target: 6–8 air changes/hour)
- Dust load
- Clearance for service access
- Cable routing feasibility
- Distance to LT panel (voltage-drop sensitivity)
Where inverter rooms are insufficient, outdoor inverter stations with IP65/67 housings may be preferable.
5. Solar Resource and Shadow Analysis
Even though advanced tools (Helioscope, PVsyst, Soliscope) will be used later, ground-truthing shadows is essential.
Record:
- Nearest tall buildings
- Chimneys (common in chemical and textile units)
- Cranes and gantries
- Parapet wall heights
Take timestamped photos at 9 AM, 12 PM, and 3 PM.
Where drone usage is allowed, capture top-down obstruction photos for precise modeling.
6. Safety and Access Considerations
Document:
- Access stairways
- Anchor points for lifeline systems
- Fragile roof zones
- Lightning protection existence and condition
EPC teams often overlook LP systems; however, DISCOM approvals sometimes require confirmation that the solar array does not interfere with existing lightning conductors.
7. Documentation Required Post-Survey
A complete industrial survey report must include:
- Roof drawings with dimensions
- Shadow analysis images
- Structural notes
- Electrical SLD (as-built)
- Load analysis summary
- Array zoning plan
- Recommendations for inverter placement
- Risks and constraints
This report becomes the foundation for design, BOQ accuracy, and client approvals.
Conclusion
A disciplined site survey prevents design mismatches, reduces rework, and ensures compliance across DISCOM and CEIG checkpoints. Vedic Solar’s structured survey process helps EPC contractors and electrical engineers produce reliable layouts, predictable yields, and clean execution workflows in West Bengal’s operating environment.