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How Many Solar Panels Do I Need?

Brian Gregory

By Brian Gregory
Published August 5, 2024

If you already understand what type of solar panels are best for your home, you’ll need to calculate how many you need. This can depend on several factors, but we have some general advice for making solar power calculations.

Solar panels on top of a home.

How to Determine the Right Number of Solar Panels

Assorted solar panels and solar panel parts on a blue background.

Once you’ve determined the right kind of solar panels for your home, look at your latest electric bill. This will help you determine your average annual energy usage, which will tell you how much electricity your solar panels must produce. Next, you’ll need to determine the necessary solar panel wattage and production ratio. You’ll use these three measurements to make your calculations.

What Is Solar Panel Wattage?

The amount of energy a solar panel produces under perfect conditions is referred to as solar panel wattage. Because no two locations receive the same amount of sunlight annually, you’ll need to factor in another element referred to as production ratio.

What Is Production Ratio?

Production ratio is the measurement of the amount of power a solar panel can produce in average weather conditions in your location. This is important to know because solar panels never operate on perfectly clear days from sunup to sundown. Each geographic region in the United States is assigned an average production ratio score from 1 to 1.6. based on weather patterns and cloud coverage.

Here’s a list of production ratios so you can understand the average weather conditions in your area:

  • Northeast: 1 – 1.3
  • Pacific Northwest: 1 – 1.15
  • Southwest: 1.5 – 1.8
  • Mid-Atlantic: 1.1 – 1.35
  • Southeast: 1.2 – 1.5
  • Mountain West: 1.3 – 1.6
  • West Coast: 1.4 – 1.8
  • Midwest: 1.1 – 1.3

Solar Panel Calculator

Here’s the formula for determining solar power. You can plug in your own numbers and use it as a solar power calculator.

To calculate the number of solar panels your home needs, divide your home’s annual energy usage, which is measured in kilowatt-hours (kWh), by your local production ratio. Then take that number and divide by the wattage of the solar panels you’re considering.

For example, if your annual energy usage is 14,000 kWh, your production ratio is 1.8 and the solar panels you’ve chosen are 320 Watts each, you’ll need exactly 24.3 panels. However, you would, of course, round up to 25 panels.

Calculating Solar Power Panels for a Home Using Square Footage

A graphic showing the correct number of solar panels for various home sizes.

Many customers ask how many solar panels they need given their home’s measurements. Although calculating the exact number of panels requires more information than a home’s size — as outlined in detail above — you can use the rough estimates below if, say, you only want to know if solar panels are even in your price range.

  • 1500 sq ft: 14-17 panels
  • 2000 sq ft: 19-25 panels
  • 2500 sq ft: 24-30 panels
  • 3000 sq ft: 27-30 panels

Can I Install Solar Panels on My Roof?

Once you know the correct number of solar panels needed to power your home, it’s important to ensure your roof can support them. Be sure to add up the weight of all the panels and compare the square footage of your roof with the total square footage of the panels. If you’re not sure your roof is in good enough shape to bear the weight, if you’re uncomfortable working on top of your house, or if you’re unfamiliar with basic safety recommendations for roof work, get a professional assessment before installation.