Some properties are well suited for producing solar energy, with ample sunshine, high electricity rates, and an ideal local climate. Unfortunately, other homes are heavily shaded and are in a cloudy climate. Therefore, certain solar systems pay for themselves in savings in several years, while others can take a couple of decades.
The sun score helps homeowners and solar installers evaluate which properties are best suited for solar panels. Calculating the sun number score of a property is an excellent way to determine its solar energy potential, taking multiple factors into account. For example, solar panels are a smart financial investment for homeowners with a high sun number but are less appealing when the sun number is low.
What Is A Sun Number?
A sun number, or sun score, is a rating between 0 and 100 that indicates the solar energy potential of a property and uses several data points. Therefore, the sun number calculation accounts for the regional climate, the hours of sunlight on the roof, and the cost of electricity from the utility company, to determine whether the home has good solar energy potential.
The Sun Number company, in collaboration with the U.S. Department of Energy (DOE), developed this tool to advance the solar power industry as part of its SunShot Initiative. Currently, 84 million homes across the U.S. have sun scores posted on the real estate website Zillow.com, making them highly accessible to the general public.
What Factors Go Into A Sun Number Score?
There are several different considerations when calculating the sun score, with some varying by location. Therefore, the factors are weighted differently using a point system to determine the total sun number score.
Building Score
Although the sun number takes several factors into account, the biggest consideration is the actual property, including the roof’s pitch, orientation to the sun, available space on the roof for PV panels, and the amount of shading. Of the 100 points, 80 come from the building score. Thus, your client’s roof will have a far bigger effect on the sun number than the cost per kilowatt-hour of electricity or the climate because it has such a big impact on the solar radiation the solar panels would receive.
Regional Climate
This portion of the sun score is calculated using solar irradiance data from the National Renewable Energy Laboratory (NREL), and it comprises 8 of the 100 points. Logically, cloudier climates have a lower regional climate score than sunny ones, but this has a relatively small impact on the total score.
Electricity Rate
The higher the utility rates per kilowatt-hour in the area, the more quickly the solar power system pays for itself through lower electricity bills and energy savings. The national average electricity rate in the U.S. is 14.8 cents per kilowatt-hour but varies considerably. For example, Hawaii and California have much higher rates, while Idaho and Washington have somewhat lower rates. Areas with higher electricity rates result in greater cost savings from PV panels.
Also, utility rates have been increasing recently. For example, the average electricity rate in the U.S. in 2021 was 13.8 cents, so it went up a cent on average in just one year.
Solar Cost
Solar energy system costs vary slightly by the installer and area of the country, and when prices are lower, the solar score will be slightly higher. For example, Arizona, Florida, and Nevada typically have some of the lowest costs. However, Indiana, New Mexico, and New York often have higher solar system costs.
What If A Client Has a Low Sun Number?
Ideally, the client will have a residential sun number score of 70 or higher to get the most benefit from installing a solar panel system. However, it might still be worthwhile for homes with a lower score to go solar, as it doesn’t take every factor into account. For example, if the homeowners really value sustainability and want to reduce their reliance on fossil fuels, a solar system might be a good idea, even if it has a long payback period.
Also, homeowners might be able to boost their sun numbers in some cases. Perhaps they could trim or remove a tree to minimize shading. If they build an addition, perhaps they can plan for adding a solar power system by adding a south-facing roof with good sun exposure. If part of the roof has good solar exposure and part doesn’t, perhaps you could install a relatively small solar system with efficient PV modules or use a ground-mount or solar carport if there is a sunny space in the yard.
Other Factors To Consider In Addition To Sun Number Score
Aside from the sun score, there are other factors to consider regarding the solar potential of a residential property. For example, a home might be located in an area with a homeowners association (HOA), and your clients may need to get approval to install solar panels. If the HOA doesn’t approve the solar system, they cannot go solar.
Likewise, some historical homes may have limitations on where the solar panels can be installed. In some cases, the PV modules cannot be visible from the front of the home, which might be the sunniest space.
Also, a solar system can be difficult to afford for some households, especially if their credit score is too low to obtain financing. In such cases, community solar might be a better option.
The sun score also doesn’t factor in how electricity costs will change over time. For example, many utility companies are planning future rate hikes, which will shorten the payback period of the solar system and boost solar energy savings.
Sun Numbers Are A Good Tool, But Not The Only Thing To Consider
Although a client’s sun score provides a snapshot of a home’s solar potential, it’s not the only factor. Diligent solar system design can help overcome roof limitations, and rising future utility costs in many areas make a solar investment more lucrative.
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