If you’ve ever browsed home listings on Zillow, you might have seen a Sun Number score. This metric, developed with the support of a grant from the U.S. Department of Energy (DOE), offered a quick way to understand a home’s solar energy potential using a scale of 0 to 100. A higher Sun Number meant better compatibility with solar panels and a higher return on investment.

However, Sun Number used a proprietary method to calculate scores, and not all of the data used is now publicly available. But if you’re curious about this metric, our guide explains how Sun Number scores were calculated and how to determine whether your home is a good fit for solar panels.

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Sun Number Score Components

Four factors went into a Sun Number score: building solar, regional climate, electricity rate, and solar cost. Although Sun Number scores are no longer widely used, the same factors still determine whether solar panels are worth it.

1. Building Solar Score (Maximum: 80 Points)

The Building Solar score was the most heavily weighted component of Sun Number scores. This score represented how suitable your roof is for solar panels, considering factors such as its size, orientation, pitch, and shading.

A higher score in this category would indicated that your roof can support solar panels in a way that captures sufficient direct sunlight throughout the day and year, making the investment in solar panels worth it. Sun Number used 3D imagery to assess a roof and determine this part of the score. 

The ideal roof for solar panels in the U.S. is a south-facing roof with no shade, a high square footage, and an angle that aligns with the latitude of the home’s location. Yet it’s rare for a roof to meet all of these criteria perfectly, and a less-than-perfect score wouldn’t mean your home is unsuitable for solar panels.

2. Regional Climate Score (Maximum: 8 Points)

Sun Number used solar irradiance data from the National Renewable Energy Laboratory (NREL) to rate the amount of sunlight your region receives. The more direct sunlight your area receives, the more electricity your panels can produce, and the higher this score would be.

3. Electricity Rate (Maximum: 8 Points)

This category represents the return on investment for homeowners. Sun Number took into account the average cost of electricity in your area and the estimated energy consumption based on the size of your house. Areas with higher average electricity rates would have a higher Electricity Rate score, as homeowners stand to save more on energy bills by going solar.

4. Solar Cost (Maximum: 4 Points)

In addition to assessing your expected financial return on solar panels, Sun Number took into account the cost of your initial investment. It used data from NREL to see the average solar installation cost in your area. The more affordable it is where you live, the higher this score would be.

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What Is a Good Sun Number Score?

The ideal total Sun Number score was 100, but it was rare for a property to rate that high. Any total score above 70 was generally considered good. It’s important to understand that—like the other online estimates—Sun Number scores were a very rough assessment of solar potential.

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How Do I Calculate My Sun Number Score?

Unfortunately, you can’t directly calculate your Sun Number score anymore. Zillow used to calculate and display Sun Number scores, but this feature is no longer available.

However, there are still a few ways to figure out if your roof is a good candidate for solar:

• Online tools: Google’s Project Sunroof tool analyzes your roof using satellite data to provide a solar potential estimate—but it isn’t available in all areas. The U.S. Department of Energy’s has a PVWatts Calculator that offers more detailed insights. You input your location, roof details, and energy usage and get a personalized solar production estimate and potential cost savings.
• Local resources: Many states and municipalities have their own solar-focused websites with localized solar potential maps, information on financial incentives, and lists of vetted installers. Try online searches using terms like “[your state] solar potential tools” or “[your city] solar resources.”
• Solar companies: Alternatively, you can skip the DIY research and contact any of our most well-regarded solar panel installers to evaluate your home’s suitability for rooftop solar. They can also walk you through local costs and incentives to help you decide if solar is worth it for you.

Check out the video below for more information about residential solar power.

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Our Conclusion

While the Sun Number scoring system is no longer used, its components are still relevant. Online tools and professionals still factor in roof characteristics, sunlight exposure, local electricity rates, and installation costs to determine whether your home is a good candidate for solar. These factors can also contribute to how many solar panels a home needs.

Consulting with professional solar installers will give you the clearest picture of your solar potential and solar panel financing options, but tools like Project Sunroof and PVWatts Calculator can be a helpful starting point. Remember that even if your home doesn’t have an ideal solar score, you might still benefit from the switch. Tax credits, incentives, and rebates can make a significant difference.

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FAQ About Sun Number Scores

What is a good Sun Number score?

A perfect Sun Score is 100, but anything above 70 is considered good.

How do I find my Sun Number score?

You likely won’t be able to find your current Sun Number score. Zillow used to display this information on real estate listings, but it’s no longer available. Instead, consider using a tool like Google’s Project Sunroof or getting a professional assessment from a reputable solar installer.

What does the Sun Number mean on Zillow?

The Sun Number on Zillow was a score (from 0-100) that indicated a home’s solar energy potential. This rating considered roof size and orientation, local weather patterns, and electricity costs. However, Zillow no longer displays Sun Numbers.

How much sun does my roof get?

You can find out how much sun your roof gets by typing your address into Google’s Project Sunroof tool. If this tool isn’t available in your area, consult a professional solar installer. They can assess your roof’s orientation, shading, and local weather patterns to give you a precise estimate.

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