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Home Solar Score: What is a Sun Number?

solar score

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. Therefore, a sun number or solar score is helpful in determining which homes are best suited for solar panels,

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, making them highly accessible to the general public.

What Factors Go Into A Sun Number Score?

Several different considerations are involved in 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 and, therefore, sun number than sunny ones, but this has a relatively small impact on the total solar 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 16.7 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 and therefore, a higher sun number.

Utility rates have also been increasing recently. For example, the average electricity rate in the U.S. in 2021 was 13.8 cents, so it went up about a penny a year.

Solar System 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. The lower the cost, the higher the sun number.

sun number

Benefits of Using Sun Numbers

There are several benefits in calculating a solar score when assessing a home for solar panels.

Accurate Assessment

Sun number provides solar installers with precise evaluations of a property's solar potential, which is critical for determining the feasibility and efficiency of solar projects. By analyzing factors such as solar irradiance, roof orientation, local weather patterns, and shading from nearby structures or vegetation, sun number generates a comprehensive score that reflects the property's suitability for solar installations.

This precision helps installers make informed decisions and optimize solar panel placements, ensuring maximum energy production and client satisfaction. The accuracy of sun number assessments reduces the likelihood of underperforming systems and helps in tailoring solutions that meet specific site conditions.

Customer Trust

Building credibility with potential customers is crucial for the success of any solar installation business, and sun number plays a vital role in this aspect. By providing transparent, data-driven recommendations based on sun number scores, installers can enhance their professional reputation and gain the trust of potential customers.

Clients appreciate clear and detailed explanations of their property's solar potential, backed by robust and reliable data. This transparency helps in setting realistic expectations and fosters a sense of confidence in the proposed solar solutions.

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 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.

Limitations of Sun Number

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.

GreenLancer can help with solar drawings and engineering reviews to optimize your client’s solar potential — complete the form below to learn more


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