What is Google Project Sunroof? How does it work?

The cost to install solar has dropped by more than 70 percent in the last decade. Yet many people still believe solar is only a luxury item for green-minded consumers rather than a smart long-term cost-saving investment. Why is this? A big reason is the lack of easily accessible information about how solar can save you money. Like EnergySage, Google's Project Sunroof is looking to fix this using technology that makes solar information available and easy to understand.

Google Project Sunroof is an initiative started by Carl Elkin, a Google engineer in Cambridge, MA. The online tool went live in 2015 to help homeowners determine if their home is ideal for solar energy and if the potential savings are worth the investment. Project Sunroof's biggest claim to fame is its solar calculator tool, which uses multiple data sources to determine how much a home would benefit from a rooftop solar installation.

The imagery provided by Google Earth creates a digital surface model, which shows the direction the roof faces (south or southwest exposure is best), the angle of its tilt, and the presence of shading objects like trees. With that information, Google determines how much sunlight hits the roof during the day by employing 3D modeling and machine learning. By adding data about local weather patterns from the National Renewable Energy Laboratory (NREL) and taking averages over a year, Project Sunroof can provide a solid baseline estimate of a roof's solar energy potential. From here, it only requires a few more calculations to give a custom cost estimate for any home.

The Project Sunroof website also offers a data explorer, which allows you to look at aggregated data for different areas of the United States and Puerto Rico and see the general solar estimate for an area. By entering the name of a city or a zip code, you can see the percentage of solar-viable buildings in that location and the median amount of roof area that buildings in that location have available for solar installation.

Like EnergySage, Project Sunroof seeks to solve the problem of information transparency in the solar industry. For many people, going solar is a challenging process that's filled with a lot of research and questions. There's no shortage of solar information and data available, but it's highly dispersed and sometimes difficult to understand for those unfamiliar with the industry and its terminology.

Project Sunroof seeks to make going solar easier by providing the public with accurate, fast, and easy-to-understand data. All you need to do is enter your address, and Google does the hard work behind the scenes, providing you with an accurate estimate of how much you could save with solar. They pair this with a "heat map" visual of your roof, giving a clear picture of its solar potential. Lighter colors represent sunnier areas, and darker tones indicate shading.

At this time, Project Sunroof has not reached every roof in the United States. Although Google continues adding new properties daily, the service is not yet available for every home. However, Project Sunroof has reached over 60 million roofs across all 50 states and most major cities from Boston to San Francisco, so there's a good chance that your home has been mapped already! This should continue to improve as Project Sunroof expands its coverage in the coming months and years.

Since it launched in 2015, Project Sunroof has continued to update its algorithms, improving the accuracy of its solar calculator tool over time. According to Project Sunroof's changelog, it hasn't been updated since 2018, so some of the data may be outdated due to new solar incentives or other changes, especially with the newly updated federal solar tax credit.

Project Sunroof also doesn't consider alternatives to rooftop solar systems. Ground-mounted solar panels may be a viable alternative to rooftop solar for properties with a large sunny area, such as a field. These systems may offer more flexibility (such as adjusting the angle of solar panels to maximize energy production) than what is typically available with rooftop solar. 
Numerous factors go into a solar calculator, and while calculators are good for providing general guidance, a professional, NABCEP-certified solar provider – like those on the EnergySage Marketplace – can give a more accurate estimate.

Because EnergySage has our own Solar Calculator, we often get questions about how our tool differs from Project Sunroof, and, truthfully, we do use Project Sunroof's data directly as part of our savings calculation! Their data mapping capabilities, combined with numbers from custom solar quotes in our Marketplace, allow us to create the most accurate solar cost and savings estimates possible.

Our process works like this: Project Sunroof tells us how much sunlight hits each part of your roof over a year. We then use this data to predict how much energy an average solar panel would generate on your roof. Once we have this number, we use your electricity bill and roof map to estimate how much electricity an array of solar panels could produce for your property. This, coupled with our Marketplace cost data for solar in your area, gives an accurate estimate of how much money you could save.

The EnergySage Solar Calculator has a couple more benefits over Project Sunroof. Even if Project Sunroof has not mapped your roof yet, we can still provide you with an estimate of your solar savings! In these scenarios, we assume 100 percent bill coverage from solar, calculate how much you would save based on solar prices and electricity rates in your area, and then add a note of how many square feet of your roof you would need to fit those solar panels.

We also show savings estimates for community solar alongside rooftop financing options in states where community solar is available. This can be especially helpful if you can't install solar panels on your roof but still want to take advantage of the sustainability and savings of solar power.

How does Project Sunroof work?

Project Sunroof utilizes Google Earth and Google Maps 3D imagery to create a digital model that looks at the direction a roof is facing, the angle of the roof, and shade factors to determine how effective a rooftop solar system would be.

How accurate is Project Sunroof?

Because a solar calculator cannot substitute a quote from a certified solar provider, consumers can expect a Project Sunroof estimate to be as much as 20 percent higher or lower than the actual cost of a new solar system.

What is a good Sun Number?

A score of 70 or more is generally considered a good Sun Number. A score below 70 means a home isn't ideal for solar; homeowners with a lower score may still see a benefit from installing solar panels.

Is my house good for solar, according to Google?

Several factors go into determining if a home is suitable for solar. We recommend exploring the Project Sunroof tool to see if Google’s data cover your address and, if so, what Project Sunroof's analysis indicates.

Get the best data from Project Sunroof and EnergySage and explore your cost savings with the EnergySage Solar Calculator. We use the most accurate information available to give you a strong estimate of how much you'll save by going solar. If you'd like to take advantage of these potential savings, create an account on the EnergySage Marketplace, and we'll provide you with competitive quotes from local installers!