Solar Panel Array Calculator
Size a solar panel array: calculate panel count, array capacity, daily/annual production, and required roof area.
Inputs
kWh/day
hours/day
NREL PVWatts: SW US 5.5–6.5 hr; SE US 4.5–5.0 hr; NW US 3.0–4.0 hr; NE US 4.0–4.5 hr
W
%
NREL PVWatts default 14%: soiling 2%; shading 3%; wiring 2%; mismatch 2%; other 5%
%
Results
Number of Panels
21 panels
Array Size
8.4 kW
Daily Production31.21 kWh
Annual Production11,391 kWh
Required Roof Area378 ft²
How to Use This Calculator
- Enter your Daily Energy Consumption in kWh/day from your utility bill or an energy audit.
- Enter Peak Sun Hours for your location — use NREL's PVWatts tool or solar resource maps (US average ≈ 4–5 hours/day).
- Enter the Panel Wattage in watts — modern residential panels are typically 350–450 W each.
- Set System Losses % to account for soiling, shading, wiring losses, and mismatch — 14% is a typical default.
- Enter the Inverter Efficiency % — string inverters ≈ 96–98%, microinverters ≈ 95–97%.
- Read the Number of Panels needed, Array Size in kW, and Required Roof Area in ft² to assess feasibility before requesting installer quotes.
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