- Solar constant (extraterrestrial): ≈1,361 W/m² [Ch 2]
- Surface peak irradiance / STC: 1,000 W/m² at 25 °C, AM1.5 [Ch 2, 4]
- Hours per year: 8,760
- Ohm’s law: V = I × R
- Power: P = V × I = I²R = V²/R
- Energy: E = P × t (kWh = kW × h)
- Series: voltages add. Parallel: currents add.
- Peak Sun Hours (PSH) = daily insolation (kWh/m²/day)
- Daily energy: kWh ≈ Array kW × PSH × Derate
- Array size: Array kW = Target annual kWh ÷ (PSH × 365 × Derate)
- Derate: ~0.83 (PVWatts default), 0.77 (conservative), 0.86 (DC-only)
- Specific yield = annual kWh ÷ kW(DC) (~1,100–1,800 kWh/kWp)
- Capacity factor = annual kWh ÷ (kW × 8,760)
- Pmax = Vmp × Imp
- Cold Voc: Voc(cold) = Voc(STC) × [1 + β(Voc) × (T_min − 25 °C)] (β negative)
- Hot Vmp: Vmp(hot) = Vmp(STC) × [1 + coeff × (T_cell,max − 25 °C)]
- Max modules/string = Inverter max DC voltage ÷ Voc(cold) → round down
- Min modules/string = MPPT minimum voltage ÷ Vmp(hot) → round up
- Max current: I = Σ Isc × 1.25 (irradiance factor)
- Min ampacity / OCPD: × 1.25 (continuous) → 1.56 × Isc overall, then apply temperature + conduit-fill derating
- Interconnection (705.12) 120% rule: Main breaker + PV breaker ≤ 1.20 × busbar rating
- Nameplate kWh = (Critical load kWh × Duration) ÷ (DoD × Round-trip efficiency)
- Usable kWh = Nameplate × DoD
- Expected string Voc = Voc(STC) × [1 + β(T_cell − 25 °C)] × N modules
- Typical acceptance tolerance: ~±5% Voc, ±10% Isc (irradiance/temp corrected)
- Performance Ratio = Actual energy ÷ Weather-expected energy