📋 Case Study

Solar Farm Design: 150 MW Utility-Scale PV Plant in Arizona

Recurring surge damage to string combiners, inverters, and SCADA RTUs due to high soil resistivity (2,500 Ω·m) and elevated lightning flash density (12 flashes/km²/yr)

🏗️ Project Overview

Desert-based ground-mount solar farm with 500 kV interconnection and central inverters

🎯 Challenge

Recurring surge damage to string combiners, inverters, and SCADA RTUs due to high soil resistivity (2,500 Ω·m) and elevated lightning flash density (12 flashes/km²/yr)

🔧 Design Approach

Deployed Type I+II SPDs rated for 10/350μs waveform at DC combiner boxes; installed deep-driven ground rods with conductive concrete backfill; applied Faraday cage design to SCADA shelters; implemented DC-side shielding with aluminum conduit bonded at both ends

📐 Design Diagram

AI-generated project design illustration

📐 Key Calculations

Ground Rod Depth Requirement

L ≥ √(ρ × t) per IEEE 142

Result: 12.2 m depth

Achieves target impedance in high-resistivity desert soil

DC SPD Energy Rating

W = 0.5 × L × I²

Result: 125 kJ per string

Withstands worst-case 10/350μs strike energy coupled into long PV strings

📊 Results

Zero SPD failures in 28 months; inverter surge-related warranty claims dropped from 22/year to 0; SCADA uptime increased from 97.3% to 99.99%

💡 Lessons Learned

•10/350μs SPDs are mandatory for DC-side protection in high-flash-density regions
•Conductive backfill compounds significantly extend ground electrode lifespan in arid climates

✅ Key Takeaways

110/350μs SPDs are mandatory for DC-side protection in high-flash-density regions
2Conductive backfill compounds significantly extend ground electrode lifespan in arid climates