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SOLAR

Solar Panel Count Calculator

Estimate how many solar panels a home needs to offset its electric bill.

JOB INPUTS

Enter your numbers

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kWh used per month (from bill)

kWh
kWh used per month (from bill)

Rated watts of one panel

W
Rated watts of one panel

Equivalent full-sun hours per day

h
Equivalent full-sun hours per day

Inverter, wiring and temperature losses

%
Inverter, wiring and temperature losses
Results update automatically
CALCULATED RESULTUSD
Panels needed21 panels
System size8.2 kW
Annual usage10800 kWh
Loss factor80 %
400 W panels21 panels
FORMULA USED900 kWh × 12 = 10800 kWh ÷ (4.5 h × 365 × 80 %) = 8.2 kW ÷ 400 W = 21 panels

HOW TO USE IT

How to use the Solar Panel Count Calculator

  1. 1

    Enter your monthly kWh usage (from your bill).

  2. 2

    Set one panel's wattage (400 W is typical).

  3. 3

    Choose your peak sun hours.

  4. 4

    Enter system losses in % (20% is common).

  5. 5

    Review panel count and system size.

THE MATH

Panel count formula

kW = annual usage ÷ (sun hours × 365 × loss factor); panels = kW × 1,000 ÷ panel wattage

Annual usage is converted to a system size using sun hours and losses, then divided by one panel's wattage to get the number of panels.

PRACTICAL EXAMPLE

A home using 900 kWh/month

900 × 12 = 10,800 kWh/year ÷ (4.5 h × 365 × 0.8) ≈ 8.2 kW. With 400 W panels, that is about 21 panels.

FAQ

Frequently asked questions

How many panels does the average home need?

Most U.S. homes need 16 to 23 panels to offset their bill, depending on usage, sun hours and panel wattage.

Should I cover 100% of my usage?

Not always. Many homes size to 80–100% for budget or roof-space reasons; net metering rules vary by utility.