Google’s Open Solar Calculator

Google announced a new free tool, Project Sunroof, that allows homeowners in a few select markets (parts of the San Francisco Bay Area), Boston and Fresno to analyze the cost and benefits of installing rooftop solar panels.

The process is very simple, you simply go to this page and enter in the address.  The software told me “Project Sunroof has not reached” my current house, but can show data for a house I used to own in Sunnyvale, California.   Using satellite data, Google shows an overview of your roof.   The tool estimates the amount of roof of your home that would receive direct sunlight.

Below is a screen shot of a satellite view of my former home in the center.  I had no large trees, and the entire house is colored yellow.  The slope of the garage facing towards the north is dark yellow.  No locations are purple, which would indicate shade.    Small sections of the neighbor’s house to the south are purple.

Source Google / Project Sunroof

Source Google / Project Sunroof

Google estimates the house receives 1,917 hours of usable sunlight per year and that 2,297 square feet of roof is available for solar panels.  The house was around 1,400 square feet but Project Sunroof also added in the garage roof and the very large awning along the west side of the house.  The name Sunnyvale indicates correctly that the climate is very sunny.

To get an accurate analysis, you also need to enter your average monthly electric bill.  That amount without air-conditioning and an electric car is relatively consistent month to month.  But this tool does not help you figure out what your bill would be if you added in an electric car.

Just for grins, I ran a test if the average electric bill for month was $100.  The system responded that the recommended solar installation size would be 3.75kW or 225 square feet and would cover 99% of the yearly usage.

The next section outlines the cost in terms of lease, loan or buy.

Cost Estimations on Sunnyvale Home

Cost Estimations on Sunnyvale Home

The tool lists the leasing costs first.  Sure there is no up front cost but your electricity will never be free.  If possible the best solution is to buy the panels and in eight years the initial upfront cost is recovered, and all electricity from then on will be free.  If someone does not have enough money to buy outright they can also take out a loan in order to eventually get free electricity from the grid.  The advantages of a lease over a loan is that the minimum maintenance and repair costs with solar are covered by the leasing company.

After the estimates are given, five solar companies are listed that you can contact.  Curiously enough Elon Musk’s Solar City is not on the list.  The press often states he is good friends with Larry Page of Google.

If the name Google (or Alphabet) was not behind this product, very little press would have occurred.  Many other solar providers have tools like this to determine the viability of solar panels, so this website is not new.  The only thing different is that you do not need to provide any contact information before beginning.    Any encouragement to keep people putting up solar panels is a great thing.





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