Solar Array Sizing

N = E_daily / (G_peak × η × PSH)

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Result
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Formula

N = E_daily / (P_panel × η_system × PSH)

Description

Solar array sizing determines how many panels are needed to meet a daily energy requirement. The calculation divides the daily energy consumption by the product of each panel peak power rating, the overall system efficiency (accounting for inverter losses, wiring losses, soiling, and temperature derating), and the peak sun hours for the location. Peak sun hours represent the equivalent number of hours at 1000 W/m² irradiance that produce the same daily energy as the actual varying irradiance profile.

Variables

  • N — Number of solar panels required
  • E_daily — Daily energy consumption (Wh)
  • P_panel — Peak power rating per panel (W)
  • η — Overall system efficiency (0-1)
  • PSH — Peak sun hours for the location (hours)

Practical Notes

Peak sun hours vary dramatically by location and season: 3-4 in northern Europe, 4-5 in the central US, and 5-7 in desert regions. Always round N up to the next whole number and add 10-20% margin for cloudy days and degradation over time. Panel output degrades about 0.5% per year, so after 25 years a panel produces about 87% of its original rating.

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