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Solar Panel Calculator

Estimate how much electricity a rooftop solar system could generate, how much it could save and how long it might take to pay back.

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Solar Energy Calculator

Enter your values below and press Calculate to see your result instantly.

Annual Energy Production
9,125 kWh
Annual Savings
$1,368.75
Payback Period
10.9 Years
System Capacity 5.0 kW

Solar sizing starts from one honest number: how much electricity your home actually uses. This calculator turns monthly usage, panel wattage and your location's sun hours into the number of panels and the system size in kilowatts that covers it.

How to use this calculator

  • Enter your average monthly electricity usage in kWh (from your bills).
  • Enter the panel wattage you are considering (commonly 400 to 550 W).
  • Enter average peak sun hours per day for your location.
  • Press calculate to see the panels needed and the system size.


Panels feast in summer and fast in winter, so systems are sized against the year's total usage, with the grid (or net metering) acting as the seasonal bank. Roof direction and shading matter as much as the headline wattage: a shaded or north-facing array can lose a quarter of its promise before it generates anything.

Frequently asked questions

How many solar panels does a typical home need?
A home using 900 kWh a month in a 5-sun-hour location needs roughly 6 kW of panels, about 13 to 15 modern 450 W panels, to match annual usage.
How do I calculate the solar system size?
Daily usage (kWh) divided by peak sun hours gives the kW needed; divide by 0.85 or so for real-world losses, then divide by panel wattage (in kW) for the panel count.
What are peak sun hours?
The day's sunlight expressed as hours of full-strength sun: a location receiving strong midday sun for 3 hours and weaker sun for 3 more might total 4.5 peak sun hours.