How Does Google Project Sunroof Work?

Project Sunroof is a free online tool created by Google to help homeowners explore the potential of installing rooftop solar panels. It uses aerial imagery and 3D modeling to analyze the size, tilt, and orientation of a home’s roof to estimate how many solar panels could fit. It also factors in how much sun exposure a roof gets throughout the year based on weather patterns and shade from nearby trees/buildings. Google launched Project Sunroof in 2015 with the goal of accelerating solar adoption by making it faster and easier for homeowners to explore solar energy.

Calculating Solar Potential

One of the most innovative aspects of Project Sunroof is how it calculates the solar potential of rooftops. The key lies in Google’s use of 3D mapping and machine learning algorithms.

After identifying rooftops in Google Maps imagery, Project Sunroof runs them through 3D modeling software to precisely measure the total square footage. This gives an accurate reading of the roof space available for solar panels.

The 3D mapping also helps analyze shading. Trees, nearby buildings, roof features like chimneys all contribute to shading, which reduces solar energy production. Project Sunroof uses the sun’s position throughout the day to simulate the exact solar exposure on every square foot of roof.

Beyond just geometry, machine learning algorithms also assess the roof’s solar orientation. The azimuth, pitch, and compass direction maximize energy production. The machine learning models draw on training data to fine-tune the shading and orientation calculations.

This sophisticated analysis using 3D mapping and machine learning sets Project Sunroof apart in its ability to provide solar potential assessments. The roof measurements quantify the physical capacity to install solar panels. And the shading and orientation optimization help predict the potential electricity generation.

Estimating Energy Production

Estimating the energy production potential of a roof is one of the most important aspects of Project Sunroof. The system takes into account a variety of factors that can impact solar electricity generation:

Weather patterns – Historical weather data is analyzed to understand the amount of direct sunlight that hits a roof in a given area throughout the year. Areas with more consistently sunny days will generally produce more solar energy.

Direction the roof faces – The orientation of the roof determines how much direct sunlight it receives. South-facing roofs in the northern hemisphere receive the most sunlight and maximize solar energy production.

Nearby trees or buildings causing shade – Any obstructions that cast shadows on a roof reduce the solar energy potential. Project Sunroof accounts for shade from trees and nearby structures that may partially block the sunlight.

By taking all these factors into consideration, Project Sunroof’s algorithms provide an accurate estimate for how much electricity a solar panel system could generate on any given roof.

Calculating Electricity Bill Savings

One of the most useful features of Project Sunroof is its ability to estimate potential electricity bill savings from installing solar panels. It does this by comparing the amount of sunlight available at your home to your past electricity bills.

When you enter your address, Project Sunroof pulls in data on your home’s electricity usage over the past year. This gives it a baseline for how much power your home typically consumes.

It then calculates the potential solar energy production at your home based on roof size, roof angle, and amount of usable sunlight. This shows how much solar power could be generated if panels were installed.

By comparing your current electricity usage to the potential solar production, Project Sunroof can estimate the percentage of your bill that could be offset by going solar. For example, it might show that rooftop solar could provide 75% of your home’s electricity needs. This would mean roughly 75% in estimated savings on your energy bills.

The estimated savings are based on the actual amount of sunlight your roof receives, your electricity costs, and your past usage. So they are customized to your home and location, providing a personalized estimate of solar savings.

Viewing Results

One of the most useful parts of Project Sunroof is the interactive map that shows the analysis of your roof’s solar potential. After entering your address, you’ll see an overhead map view of your roof. The map will display color coding to indicate the solar potential of different areas of the roof – red means high productivity, yellow is moderate, blue is low.

In addition to the color coding, the map provides specific stats on how much sunlight your roof receives, the square footage available for solar panels, and the estimated capacity in kilowatts if you installed panels. You’ll also see the predicted energy production per year measured in kWh based on the available roof space.

One of the key numbers is the estimated electricity bill savings per year. Project Sunroof calculates this by taking into account energy rates in your utility district and how much solar power could offset your usage. This gives you a realistic estimate of how much money you could potentially save by going solar.

The interactive map is a great feature because it lets you visually understand how much sunlight your roof gets and view custom calculations for energy production and cost savings. This data makes it easy to evaluate the financial payoff if you decide to invest in solar panels.

Getting Quotes

One of the most useful features of Project Sunroof is the ability to get quotes directly from pre-screened solar installers in your area. After entering your address and viewing your solar analysis, you have the option to request quotes from local installers right within the Project Sunroof interface.

This is powered by Google’s Local Services program, which connects users to qualified home service professionals who have been background checked and meet licensing requirements. When you request solar quotes through Project Sunroof, your information is sent to installers in your area who are part of the Local Services program.

The installers then reach out directly to you to provide a free, no-obligation quote for installing solar panels on your home. They can factor in your specific solar potential analysis from Project Sunroof when putting together their quote. This makes the process smooth and efficient.

Requesting quotes through Project Sunroof removes the need to search for and vet installers on your own. You can feel confident using a service provider verified by Google. It streamlines the process and allows you to easily comparison shop quotes from multiple qualified local installers.

Expanding to More Locations

Currently, Project Sunroof is only available in certain parts of the United States where there is sufficient data to provide solar estimates. When the project first launched in 2015, it was limited to just a few cities in California and the Boston area. Since then, Google has expanded Project Sunroof’s coverage significantly, bringing the solar calculator tool to 42 states. However, there are still many parts of the U.S., particularly more rural areas, that are not covered by Project Sunroof.

Google has stated plans to continue expanding Project Sunroof to more regions in the coming years. The main challenge is obtaining the necessary data, including high-resolution aerial imagery and 3D modeling of local homes and trees, which Google uses to customize the solar analysis for each address. As Google continues mapping more neighborhoods with its Street View cars equipped with roof-mounted cameras, Project Sunroof’s reach grows. Google is actively working to bring its solar calculator to even more homeowners over time.


While Project Sunroof provides valuable information about solar potential, it does have some limitations to consider:

The estimates do not take into account every factor that can impact solar production. For example, Project Sunroof does not consider roof condition, which can affect whether installation is possible. It also does not account for partial shade from nearby trees or buildings, which can reduce energy production. In addition, the estimates are not optimized for new construction or major roof renovations.

The analysis focuses solely on the roof area visible from aerial imagery. Features like solar carports and ground-mount systems are not factored into the estimates. Energy use and electric bill amounts are estimated based on location and home size, not actual utility data.

Overall, Project Sunroof provides a good starting point to assess solar potential. However, a site survey by an installer would provide estimates tailored to the specifics of your roof and energy use. Their analysis can account for factors Project Sunroof does not consider.

Comparable Services

There are several other online tools and services that provide similar solar analysis functionality as Project Sunroof. While Project Sunroof relies on Google’s high-resolution aerial imagery and advanced 3D modeling, some competitors use different technical approaches for estimating solar potential. Here is an overview of some comparable services: allows users to get a quick estimate of solar potential and savings based on address. It analyzes sun exposure using lidar data and provides basic system specs and cost estimates. However, it does not generate detailed 3D models like Project Sunroof.

Geostellar provides customized solar estimates by analyzing satellite imagery, weather data, and utility rates. It offers more detailed system sizing and financial analysis compared to Project Sunroof. Their online reports include panel recommendations, estimated production, ROI, incentives, and financing options.

Sunmetrix is a solar lead generation company that offers free personalized solar estimates. They use aerial scans, shading analysis, and machine learning algorithms to assess site suitability and provide ballpark system specs and savings. Sunmetrix aims to connect homeowners with local installers.

While these tools offer useful basic analysis, Project Sunroof stands out with its sophisticated 3D modeling powered by Google’s advanced geospatial technologies. The level of detail in its solar production estimates and easy-to-use interactive experience make it one of the premier solar calculators available online.

The Future of Project Sunroof

Project Sunroof has great potential to expand and improve in the future. Here are some ways we may see the service evolve:

Expanded availability – As Google continues mapping rooftops with LiDAR technology and imagery, Project Sunroof can roll out to cover more regions and cities around the world. The goal is to eventually provide solar estimates for every suitable roof.

Enhanced accuracy – With improved 3D modeling and solar simulation algorithms, the energy generation and bill savings estimates can become even more precise. Google may incorporate real-time weather data for hyperlocal solar projections.

Additional features – We may see new features like showing system payback periods, CO2 emission reductions, or calculations for adding home batteries. Comparisons to wind, geothermal or other renewable options could be included.

Utility integration – Direct integration with local utility companies to factor in net metering policies, retail electricity rates, and other incentives could provide a seamless experience from estimate to installation.

Contractors marketplace – Project Sunroof could evolve into a solar marketplace by connecting users to pre-screened local installation companies to take the next steps and request quotes.

With Google’s resources and continued innovation, Project Sunroof is poised to become an indispensable tool for many homeowners considering solar power in the years ahead.

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