📋 Case Study

Solar Farm Design: Grounding for PV Arrays with Rapid Shutdown & Lightning Exposure

Lightning-induced backfeed damaging inverters and failing NEC 690.43(C) rapid shutdown grounding continuity requirements

🏗️ Project Overview

220 MWac utility-scale solar farm in West Texas

🎯 Challenge

Lightning-induced backfeed damaging inverters and failing NEC 690.43(C) rapid shutdown grounding continuity requirements

🔧 Design Approach

Hybrid ground grid combining driven rods, buried bare copper rings, and concrete-encased electrodes (Ufer), with SPDs bonded directly to grounding conductors

📐 Design Diagram

_ground = 87% of I_total Z_SPD / (Z_SPD + Z_ground) R_cont ≤ 25 Ω → Achieved: 12.4 Ω NEC 690.43(C)(2) Grounding Conductor SPD / Equipment Bond Ufer Electrode Lightning Risk

AI-generated project design illustration

📐 Key Calculations

Lightning Current Division

I_ground = I_total × (Z_spd / (Z_spd + Z_ground))

Result: 87% diverted to ground

SPDs remain within 20% derating margin

Rapid Shutdown Ground Continuity

R_cont ≤ 25 Ω (NEC 690.43(C)(2))

Result: 12.4 Ω

Validated via 10A DC continuity test per UL 1741 SB

📊 Results

Zero inverter failures due to surge events over 28 months; passed all AHJ inspections on first submission

💡 Lessons Learned

•PV module frames must be bonded every 3rd racking post—not just at ends
•Ground continuity testing must be performed *after* torque verification of all lugs
•Soil drying in summer requires seasonal resistivity retesting and supplemental grounding augmentation

✅ Key Takeaways

1PV module frames must be bonded every 3rd racking post—not just at ends
2Ground continuity testing must be performed *after* torque verification of all lugs
3Soil drying in summer requires seasonal resistivity retesting and supplemental grounding augmentation