What structural and electrical data is required to perform a detailed solar feasibility survey for a factory?
Structural & Civil Data Requirements
The primary objective is ensuring the roof structure can support the additional dead load (panels, mounting structures, ballast, cabling) and dynamic environmental loads (wind uplift, seismic activity) without compromising structural integrity.
- Roof Architecture & Type:
- Structure Class: Reinforced Cement Concrete (RCC), metal sheet (Corrugated, Standing Seam, Trapezoidal), or hybrid truss.
- Roof Dimensions & Usable Area: Total footprint versus effective shadow-free area (accounting for HVAC units, skylights, exhaust vents, parapets, and water tanks).
- Pitch & Azimuth: Roof tilt angle (degrees) and compass orientation (optimal orientation in Bangladesh is true South, 180^\circ azimuth, with a 15^\circ \text{--} 23^\circ tilt).
- Load-Bearing Capacity & Structural Engineering:
- Dead Load Limit: Existing roof load capacity (\text{kg/m}^2 or \text{psf}). Typical commercial solar arrays add 12 \text{--} 25 \text{ kg/m}^2 depending on ballast versus penetrating/clamp mounts.
- Purlin / Structural Framing Specs: Spacing, thickness, and material specification (gauge) of purlins and rafters under metal roofs.
- As-Built Structural Drawings: Original structural design consultant drawings, concrete strength rating (\text{psi}), and column layout.
- Site Dynamics & Access Logistics:
- Wind Load Conditions: Local wind speed parameters per building code (BNBC standards specify basic wind speeds up to 210 \text{--} 260 \text{ km/h} in coastal industrial regions).
- Roof Condition & Waterproofing: Age of roof, current leakage points, corrosion levels on metal sheets, and type of waterproofing membrane.
- Crane & Cable Pathways: Logistics access for lifting modules, structural steel, and inverters during construction.
Electrical System Data Requirements
Electrical data determines system interconnection, inverter sizing, protection coordination, and compliance with utility net-metering limits.
- Grid Connection & Tariff Profile:
- Sanctioned & Connected Load: Offtaker’s sanctioned demand (\text{kW} or \text{kVA}) from the utility (e.g., REB, BPDB, DESCO, DPDC). Net metering capacity limits are tied directly to sanctioned load.
- Transformer Specifications: Rated capacity (\text{kVA}), primary/secondary voltage levels (11 \text{ kV} / 0.415 \text{ kV} or 33 \text{ kV} / 11 \text{ kV}), percentage impedance (\%Z), and operational headroom.
- Substation & Switchgear Details: Breaker ratings, busbar current carrying capacity, space availability inside LT/HT panels for dedicated solar AC breakers.
- Consumption Profiles & Power Quality:
- 12-Month Historical Electricity Bills: Monthly energy consumption (\text{kWh}), maximum demand (\text{kVA}), and power factor trends.
- Interval Load Profiles: 15-minute or hourly load data (from smart meters/data loggers) to match generation profiles with factory operating shifts (e.g., 24/7 vs 12-hour daytime duty).
- Power Factor & Harmonics: Existing power factor correction (PFC) capacitor banks and Total Harmonic Distortion (\text{THD}) levels to avoid anti-islanding and inverter tripping.
- Backup Generator & Microgrid Infrastructure:
- Diesel Generator (DG) Synchronizing Data: Total active DG rating (\text{kVA}), controller specs (Deep Sea, ComAp), and minimum load requirements (typically 30\% minimum loading required to prevent wet stacking).
- Zero-Export / Fuel-Save Systems: Requirements for PV-Diesel hybrid controllers to automatically throttle solar output during grid outages.
- Earthing & Surge Protection:
- Soil Resistivity & Earth Pit Values: Measured earth resistance (\Omega) of existing factory earth pits.
- Lightning Protection System (LPS): Location of existing air terminals/faraday cages and requirement for dedicated solar earthing pits.
Technical Data Checklist Summary
| Domain | Key Parameter | Engineering Impact |
|---|---|---|
| Structural | Usable Shadow-Free Roof Area (\text{m}^2) | Determines maximum module count and system capacity (\text{kWp}) |
| Structural | Structural Load Allowance (\text{kg/m}^2) | Dictates mounting hardware (ballasted, clamped, or direct penetration) |
| Electrical | Sanctioned Load (\text{kW}) & Transformer Capacity | Sets legal and physical limits for grid-tied AC export |
| Electrical | Daytime Load Profile (\text{kW} vs Time) | Optimizes self-consumption ratio and prevents excessive curtailment |
| Operations | DG Plant Specifications & Controller Type | Configures PV-Diesel integration and zero-export protection controls |