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What Is A Sun Number And How Do You Find Your Home’s Sun Score?


Have you ever thought of going solar but don’t know if your home has good solar potential? Is your property too shaded, or is your regional climate too cloudy for solar panels? Calculating your sun number is a great way to determine the solar energy potential of your property, taking multiple factors into account.

Solar panels are likely a great idea and a sound financial investment if you have a high sun number. However, if your sun number is low, you might want to reconsider.

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Sun Number Meaning

A sun number, or sun score, is a number between 0 and 100 that assesses the solar power potential of a property. The number considers such factors as regional climate, the amount of sunlight the roof receives daily and any shade from nearby trees to determine whether the home is a good candidate for solar energy upgrades.

The Sun Number company developed this tool in collaboration with the U.S. Department of Energy as part of its SunShot Initiative to advance the solar industry. Now, 84 million homes have their sun scores listed on Zillow.

What Is A Good Sun Number?

A sun number of 70 or higher isideal for those looking to get the most benefit from adding solar panels to their roof. However, homes with a slightly lower score may still find that solar upgrades are a wise financial investment in certain circumstances.

Although the sun number takes many factors into account, the biggest consideration is your property itself, including the pitch of the roof, orientation with the sun, available roof space for solar panels and shading. Thus, your roof will have a much bigger impact on your sun score than utility electricity rates or your climate.

In some cases, it might be possible to improve your sun number. For example, you might be able to trim or perhaps remove a tree to reduce shading dramatically. If you build an addition, you can plan for installing a solar energy system by trying to add a south-facing roof with good solar exposure. If part of your roof is shaded and part isn’t, perhaps you could install a smaller solar system with high-efficiency solar panels or use a ground-mount for your array if there is a sunny corner of the yard.

If your electricity rates go up, it will cause your sun number to increase as well. Also, really good solar incentives can help overcome a low solar score. For example, if you qualify for tax credits or utility rebates, it can make the solar system a better investment, regardless of having a lower sun number.

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How Is My Sun Score Calculated?

Let’s examine the factors used in determining your sun number.

  • Building Solar Score: up to 80 points - By far, the biggest consideration is related to your home itself, not external factors.
  • Roof pitch - The incline of your roof impacts how the sun hits the solar panels. The ideal angle corresponds with your latitude because it affects how high the sun is in the sky.
  • Roof orientation - Ideally, your roof is south-facing for maximum solar energy production throughout the day. An east-facing roof will generate more solar electricity in the morning, while a west-facing roof produces more power in the afternoon.
  • Roof size - Ideally, your roof is large enough for a solar system that can produce all the electricity your home needs.
  • Roof shading - Trees and buildings can block the sun, reducing your solar energy output.
  • Regional Climate Score: up to 8 points - This score is calculated using solar irradiance data from the National Renewable Energy Laboratory (NREL). Thus, cloudy climates do not rank as high.
  • Average Cost of Electricity: up to 8 points - The higher the cost of electricity in your area, the quicker the solar system will pay for itself in utility bill savings. The national average electricity rate per kilowatt-hour is 13.7 cents, but it varies considerably across the country.
  • Solar Installation Cost: up to 4 points - Solar system installation costs vary slightly. For example, Florida, Nevada and Arizona tend to have some of the lowest costs, whereas Indiana, New Mexico and New York can have higher installation costs.

Where Can I Find My Home’s Sun Number?

Sun Number partnered with the real estate company Zillow in 2016 to enable homeowners and homebuyers to view sun numbers by simply entering the address at Now, many properties have the sun number in the Zillow listing, helping home shoppers to consider a property’s solar potential before making a purchase. There are many properties that still do not list the sun number, however.

For homebuyers who are serious about installing solar, it helps them easily determine if a property is well-suited for solar panels. Likewise, current homeowners can use this feature to learn the sun number of their home (if one of the 84 million). If you can’t see your property’s sun number on Zillow, learn how to assess the solar potential yourself.

The Bottom Line: Your Sun Number Can Help Determine If Solar Is Right For You

Although many homes have good solar potential, unfortunately, some do not. The sun number rating system was created to help people quickly determine if a solar system is a wise financial investment by rating the solar potential and cost-savings opportunity. For example, if a home has a score of over 70, a solar system is a good way to potentially reduce electricity bills and greenhouse gas emissions dramatically.

Are you ready to install solar panels on your home? Consult a Rocket SolarSM Advisor to get started.

Powered By The Sun

Tap nature's energy for your purposes. Let us know you're interested in solar.

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