When browsing homes on Zillow, you may have come across a Sun Number score. This rating, created with funding from the U.S. Department of Energy (DOE), helps homeowners quickly assess a property’s potential for solar panel energy. The scale runs from 0 to 100, with higher scores indicating better solar compatibility and a stronger return on investment (ROI).
Although Sun Number relied on a proprietary formula, not all of the data behind the scores remains accessible today. Still, if you’re interested in understanding what the score means, this guide breaks down how the system works and how to figure out if your home suits solar panels. We also reviewed the best solar companies to help you choose the right provider once you’re ready to invest in a solar panel system.
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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 indicate 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 uses 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 will 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 will be.
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.
Quick Tip
- For a more accurate assessment, individuals interested in solar should reach out to multiple local installers who can provide specific evaluations of their properties.
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 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.
How Do I Improve My Home’s Sun Score?
Improving your home’s Sun Number score starts with maximizing its exposure to sunlight. Trim or remove any tree branches that block solar access, and consider installing panels on the part of your roof with the fewest obstructions. Position your panels on a south-facing section of the roof, which typically receives the most direct sunlight throughout the year. A lighter-colored roof can also help by reflecting heat, which reduces overall energy consumption and contributes positively to the score.
You can also boost your score by optimizing the angle and tilt of your solar panels. Work with your installer to find the ideal orientation for your location and roof type. Choosing high-efficiency panels or upgrading to newer technology can increase your solar system’s overall performance. These improvements not only enhance your Sun Number score but also improve your energy savings.
Our Conclusion
While the Sun Number scoring system no longer remains in use, its core elements still play an important role in evaluating your home’s solar potential. Tools like Project Sunroof and PVWatts Calculator assess key factors such as roof orientation, sunlight exposure, electricity rates, and installation costs. Professional solar installers can offer a more tailored analysis, such as how many solar panels your home needs, and outline the best solar financing options based on your location and energy needs.
Even if your home doesn’t earn a high solar rating, you may still benefit from switching to a full or hybrid solar system. There are federal tax credits, local incentives, and rebates that can significantly lower installation costs and improve your long-term return on investment.
FAQs 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.