Solar Panel Array Calculator

Size a solar panel array: calculate panel count, array capacity, daily/annual production, and required roof area.

Daily Energy Requirement

kWh/day

Peak Sun Hours

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

Panel Wattage

System Losses

NREL PVWatts default 14%: soiling 2%; shading 3%; wiring 2%; mismatch 2%; other 5%

Inverter Efficiency

Tab to move between fields

Number of Panels

21 panels

Array Size

8.4 kW

≈ 8 microwaves

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.

How the result changes with Daily Energy Requirement

Daily Energy Requirement: Average daily energy consumption to be offset by solar (from utility bill).
Peak Sun Hours: Average daily peak sun hours (insolation) per NREL PVWatts and NASA SSE data. Southwest US (Phoenix/Las Vegas): 5.5–6.5 hr; Southeast (Atlanta): 4.5–5.0 hr; Northwest (Seattle): 3.0–4.0 hr; Northeast (Boston): 4.0–4.5 hr.
Panel Wattage: STC rated wattage of each solar panel. Modern residential: 350-450W.
System Losses: Total system losses from soiling, shading, wiring, mismatch, etc. per NREL PVWatts defaults. Breakdown: soiling 2%; shading 3%; snow 0%; mismatch 2%; wiring 2%; connections 0.5%; light-induced degradation 1.5%; nameplate 1%; total ~14%.
Inverter Efficiency: DC-to-AC conversion efficiency of the inverter. Typical: 95-98%.

Identify Input Parameters
4 parameters
Daily Energy Requirement = 30, Peak Sun Hours = 4.5, Panel Wattage = 400, System Losses = 14 = 5 input(s) provided
Calculate Number of Panels
Number of Panels
21 = 21
Calculate Array Size
8.4 = 8.4
Calculate Daily Production
Daily Production
31.21 = 31.21
Calculate Annual Production
Annual Production
11391 = 11391