What is a sun score? Sun Number rating explained

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Sun Number

UPDATE: As of 2023, Sun Number's website is no longer functional, and Sun Number scores no longer appear on Zillow. Below, you can find our original article on this topic, for your reference.

If you've shopped for solar before, you may have encountered "Sun Number" or sun score. Like EnergySage, Sun Number received funding from the Department of Energy's SunShot initiative to innovate in the solar energy space. Read on to learn more about how a property's Sun Number is calculated and what your sun score means for going solar.

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Key takeaways

  • A sun score is a way to measure a home's solar potential

  • Sun Number uses aerial imagery and factors like shading, trees, regional climate, roof shape, and more to come up with a score

  • You can check your property's solar suitability with our Solar Calculator and compare solar quotes by registering for free on the EnergySage Marketplace

A home's Sun Number score measures its suitability for solar power on a scale from 1 to 100. Sun Number, a recipient of a grant, developed the methodology behind the score as part of the Department of Energy's SunShot Initiative.

Notably, just like any measure of solar suitability, your property's Sun Number is only one data point to consider. Solar installations are unique to each home depending on electricity usage, location, pricing, and more, and it's always best to compare solar quotes to understand how feasible solar is for you. To get started comparing solar quotes from local, qualified installation companies, register on the EnergySage Marketplace for free today.

Sun Number scores consider four main categories of factors to create a total score. The categories are all weighted differently. These categories are:

  • Building

  • Climate

  • Electricity rates

  • Cost of solar


The building solar score for a Sun Number is the rating system's most extensive and detailed part. Several factors contribute to this portion of a sun score, including roof design, size, roof pitch and orientation (also known as the roof plane), and shading, all of which Sun Number generates from aerial roof imagery. In general, a south-facing roof with lots of space, no shade or obstructions, and an angle matching the latitude of the property's location is the best kind of roof for solar and will receive a high building score as part of its overall Sun Number.

While Sun Number is no longer available, this is the same type of information that powers the EnergySage Solar Calculator! We use roof data, sun exposure data from Google's Project Sunroof, and our market pricing data to estimate how suitable your home is for solar and how much you could save.


The following three score categories that factor into a total Sun Number are more straightforward than the building score, starting with climate or the regional climate score. Different areas of the country receive different amounts and intensities of sunlight and have varied weather conditions, so a home's solar suitability is related to its location. For example, in higher latitudes like the Northeast or Pacific Northwest, sunlight is, on average, weaker throughout the year than it is somewhere like Texas or Florida. The amount of sunlight throughout the year leads to a higher climate portion of a Sun Number score because you can usually expect a higher energy output from your solar panels. Sun Number gets its solar radiation (or solar irradiance) data from the National Renewable Energy Laboratory (NREL).

Electricity rates

Installing solar panels helps most homeowners with cost savings on their electricity bills, so it follows that places with a higher cost of electricity are more suitable for solar installations, as those installations will have a shorter payback period. Sun Number factors this into their total score: higher average electricity rates mean a higher sun score, and lower average electricity rates mean a lower sun score.

Cost of solar

Lastly, just like a high cost of electricity makes an area more suitable for solar, so does a low cost of solar. A total Sun Number score considers the local average cost of solar – lower average costs mean a better sun score, and higher average costs mean a worse sun score. This is the same as the reasoning behind how electricity rates impact your sun score, just in the opposite way. Low solar costs mean your upfront installation price is lower; therefore, making back the money on your initial solar investment will take less time. Conversely, a high upfront cost of solar means it will take, in some cases, several more years to make back your initial solar investment.

A Sun Number score or other calculators can help you assess a home's potential savings with a solar panel system. So, if you're considering installing solar panels and looking for a home with solid solar energy potential, check this out before making an offer. You could also ask a solar installer for an estimate on a solar energy system on any real estate property before you make an offer.

Using a tool like Sun Number to understand your property's suitability for solar can be an important initial step in any solar journey. However, it's not the only data point you should consider, and a low Sun Number score doesn't mean you shouldn't consider solar!

Once you're ready to start comparing solar quotes, you can register (for free!) on the EnergySage Marketplace. We'll connect you with qualified, pre-vetted solar installers in your area, and you can compare quotes from those companies on our platform, entirely online.

Find out what solar panels cost in your area in 2024
Please enter a five-digit zip code.
  • 100% free to use, 100% online
  • Access the lowest prices from installers near you
  • Unbiased Energy Advisors ready to help
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