Solar Array Sizing — Method
Size the array from energy, not power: take your average daily consumption (kWh/day), divide by the location peak sun hours, and divide again by a performance ratio that captures inverter, temperature, wiring and soiling losses (typically 0.75–0.8). That gives the DC array kW. Divide by the panel wattage and round up for the panel count. For grid-tie, also check export limits; for off-grid, pair with battery and inverter sizing.
Frequently Asked Questions
Array kW = daily kWh divided by (peak sun hours x performance ratio, ~0.77). Then panels = array watts divided by panel watts, rounded up. For 10 kWh/day at 5 sun hours that is about 2.6 kW, or seven 400 W panels.
The equivalent number of hours per day at 1000 W per square metre. It varies by location and season; typical annual averages are 3-6 hours. Use local irradiance data for accuracy.
The fraction of theoretical output actually delivered after inverter, temperature, wiring and soiling losses, typically 0.75-0.8. Lower it for hot climates or shaded/soiled arrays.
A small oversize (DC/AC ratio 1.1-1.3) captures more energy in poor light and offsets degradation, but check inverter clipping and any export limit.
It sizes the array for daily energy. Off-grid systems also need battery autonomy and inverter sizing, which you can do with the battery bank and inverter calculators.
Solar Array Sizing Explained
A solar array is sized to replace energy, so the starting point is your daily kWh, not your peak watts. Dividing by peak sun hours converts energy to power, and the performance ratio accounts for the real-world losses between the panel nameplate and useful output.
From energy to panels
Daily kWh ÷ (sun hours × PR) gives the DC kW the array must be. Divide by the module wattage for the count, rounding up. Hotter sites and shaded roofs need a lower PR and therefore more panels.
Next steps
For a complete design, pair this with battery bank sizing, inverter sizing and PV string sizing, plus DC cable sizing.
Related: Battery Bank, Inverter Sizing, PV String.