| AWG / kcmil | Cu 60°C | Cu 75°C | Cu 90°C | Al 75°C |
|---|
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Select your state and enter building details to see how many solar panels you need to power your AC.
⚡ AC Circuit Sizing (Mode 1)
Following NEC 690.8(A)(1), the continuous load is calculated as:
I_design = (W_total / V / PF) × 1.25
Wire ampacity is then derated for ambient temperature (Table 310.15(B)(1)) and conduit fill (Table 310.15(C)(1)) to find the required ampacity. NEC 690.9(B) requires the breaker to be rated ≥ 125% of rated AC current, rounded up to the next standard size.
120% Rule (NEC 705.12(B)(3)): Solar backfeed breaker + main breaker ≤ 1.20 × busbar rating. Voltage drop uses: VD% = (2 × L × R × I) / (V × 1000)
❄️ Solar for AC (Mode 2)
Cooling load is estimated using IECC climate zone BTU/sqft benchmarks and adjusted for ceiling height, insulation quality, occupant loads, and sun exposure — a rule-of-thumb approximation within ±25% of Manual J.
AC daily kWh = W_ac × runtime / 1000. Panels needed:
Panels = kWh_daily / (PSH × panel_W / 1000 × efficiency)