Appendix E: Unit Conversions & Reference Tables

Power & energy

• 1 kW = 1,000 W; 1 MW = 1,000 kW
• 1 kWh = 1,000 Wh; 1 MWh = 1,000 kWh
• 1 kWh = 3.6 MJ

Irradiance

• 1 “sun” = 1,000 W/m² (STC reference)
• 1 kW/m² = 1,000 W/m²

Length & area

• 1 m = 3.281 ft; 1 ft = 0.3048 m; 1 in = 25.4 mm
• 1 m² = 10.76 ft²

Structural load / pressure

• 1 psf = 47.88 Pa; 1 kPa ≈ 20.9 psf
• Typical module dead load (with racking): ~3–6 psf [Ch 25]
• Typical roof maintenance live load: ~20 psf [Ch 25]

Temperature

• °F = (°C × 9/5) + 32; °C = (°F − 32) × 5/9
• A coefficient in %/°C × ΔT(°C) gives the % change [Ch 4, 15]

Mass

• 1 kg = 2.205 lb; a typical residential module ≈ 20–25 kg (44–55 lb)

Handy planning reference values

• Residential module (2026): ~400–450 W, ~2 m², TOPCon ~22–23% efficient [Ch 5]
• Quick derate for estimates: 0.80–0.83 [Ch 14]
• Healthy performance ratio: ~0.75–0.85+ [Ch 34]
• DC/AC ratio: ~1.1–1.3 [Ch 16]
• NEC conductor factor: 1.56 × Isc (then derate) [Ch 16]
• Rapid shutdown: ≤30 V outside / ≤80 V inside, 30 s, 1-ft boundary [Ch 22]
• Fall-protection trigger (install): 6 ft (construction) [Ch 27]

⚠️ Wire ampacities are not tabulated here on purpose: always size conductors from the adopted NEC edition’s ampacity tables with the correct temperature and conduit-fill corrections (Ch 16). A primer table would tempt edition-blind shortcuts.