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Here’s Our Guide to Google’s Project Sunroof

On August 18th, 2015, Google announced the launch of Project Sunroof, its new tool to help homeowners find out their roof’s solar potential and connect with installers in their area to begin the process of getting quotes and deciding how to pay for it. It uses a modified version of Google Maps to bring up 3-D models of your roof and the surrounding trees and estimates the incoming solar radiation and automatically to show you how much energy you could generate.

Once you’ve entered your address, the site pulls up a map of your roof and performs the beginning calculations. You can fine-tune the estimate by adjusting your monthly energy bill, which will prompt the system to automatically adjust its proposed system size to meet your needs. Once you’ve decided on the size of your system and seen the savings estimates provided, you can enter your contact information to be sent to Google’s solar installer partners.

At launch, the service was only available in three areas: Boston, Massachusetts, the San Francisco Bay Area, and Fresno, California. In December, the service expanded to 12 other metro areas in Arizona, Connecticut, Nevada, New Jersey, New York, and North Carolina.

This could prove to be a gamechanger for the home solar industry once it’s available in all areas of the country, but it isn’t designed to be helpful to people interested in the process of going solar. We like to think that’s our job, so we’ve prepared this post to answer some of the questions—big and small—about using Google’s tool and what happens after you click “Submit.”

Here’s what we’ll cover in the following article:

How does Project Sunroof work?

We all know the Internet is a series of tubes, but how does this tube do the work it does? Well, you might know Google for its famously awesome maps of everything from Toledo to the surface of the moon, and it’s these maps that power Project Sunroof. Specifically, Google has found a way to not only measure your roof’s size, but also decide whether your neighbor’s giant oak is going to block some of the sun you might otherwise get.

They start by creating a 3-D model of your roof and any nearby trees. Then they overlay an average solar radiance map. The result is a little model of your house that shows exactly how much sun you can expect on your roof over a year. Here’s what it looks like after you give Project Sunroof your address:


Et voila.

Here’s a little more detail of what the house looks like:

That’s pretty cool, huh? But it might not be perfect, yet. One concern we have about this is that this tool isn’t as accurate as it needs to be. That southwest-facing roof you see there is ideal for solar, but the trees in the image, particularly the one on the southeast corner of the house, don’t seem to be modeled accurately. The worst thing that can happen to a solar installation is to be in shade, so we hope Google gets this exactly right as this project moves forward. Having an accurate picture of sun and shade is vital to producing good data about the savings you can expect with solar.

How do they determine how much solar I need?

Google begins with a mid-range estimate for how much electricity you might use every month, then determines if the space you have available on your roof is enough to hold the panels you’ll need to meet close to your full usage. That sentence is kind of complex, so let’s break it down:

The first thing you need to know to calculate the amount of solar you should have is how much electricity you use. Most homeowners will not want to exceed their usage, because, depending on the state they live in, they probably won’t get credit or any production over their yearly usage. But getting close to your full usage is great, because it means you save more money.

In our example of a home in the Bay Area, Google started with an estimate of $125 monthly electric bill, which is just a titch higher than the average California home’s usage. Here’s how the numbers break down: Given an average of 20.5 cents per kilowatt-hour (kWh), Google estimates that our example home uses about 610 kWh per month, or 7,320 kWh per year.

Once they know how much usage you need to meet with solar, Google determines if the roof space you have available is enough to hold the panels needed to meet it. Google’s estimate for our example house showed a 5.25-kW system that would cover an area of 370 square feet and produce 98% of the energy we’d need for the year.

We performed our own calculations, and these are the numbers we came up with: The installation represented by this estimate would be 31 panels that are each rated to produce 170 watts. The system would be facing south/southwest on the roof of our house, and would produce about 7,166 kWh per year. Those numbers closely match the Google estimates, meaning they’re pretty accurate, if their shade profile is correct.

What does my electricity bill have to do with it?

The electricity bill is what determines how much you can save with solar. PG&E is the electric utility that serves our example home, and the average rate for electricity from them is 20.5 cents per kWh. That’s 64% higher than the national average for electricity cost, and it means solar saves you more money in California.

That’s part of the reason the solar industry has flourished in the state. It surely isn’t hours of sunlight, which in the Bay Area are about the same as in South Dakota or Nebraska. The electricity prices in California have been so high for so long that even when solar was more expensive, it made sense. So the big question is:

Are their financial estimates fair and accurate?

Short answer? Actually, yeah, with caveats. The estimate we grabbed above for an relative’s house said we’d end up with $9,000 in savings from a 20-year lease, $7,000 in savings from a loan, and $21,000 if we put the money down up front. Here’s a cropped version of how that looks on the Sunroof interface:

There’s a couple of strange things about the numbers above.

  • For the lease, $9,000 in savings over 20 years would be an average of $450, not $500
  • For the loan, $7,000 in savings over 20 years would be an average of $350, not $400
  • For the purchase, the $14,000 initial cost is a little low. Solar prices aren’t that low in California yet.

Other than those strange things, they mostly get the numbers right. Our own numbers show the upfront purchase option to cost $17,500 up front, with 20-year benefits that total $37,500, for a net profit of $20,000.

For a $17,500 loan with 5% interest, we estimate a 20-year savings of about $12,000. The Google Sunroof estimate looks more like a $17,500 loan at 8%, so depending on the rate you can get on a large loan, you’ll probably fall somewhere between the two.

Looking Forward for Sunroof

So far, Google’s Project Sunroof is a really neat tool for people in certain areas of the country. We’re pretty jazzed about the technology behind it, and making the process of going solar clearer and less complicated is something we’re always happy about. It’ll be interesting to see whether they stay working within the large urban centers they’ve chosen so far, or if they’ll expand the tool to be useful for everyone.

And boy, we’d love to use their API for the solar roof maps on our own site. Are you listening, Google?

Last modified: January 7, 2016

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3 thoughts on “Here’s Our Guide to Google’s Project Sunroof

  1. Anonymous says:

    I DID, BUT YOU CUT ME OFF, so much for freedom of speech!

  2. P. Bolino says:

    Read about Nevada’s PUC & what they did to homeowners who had installed solar, and the in-screw-shable cost increases of NV homeowners, increases expected, and will it hapen to California homeowners, because: PG&E, NV-PUC,AND DUKE ENERGY appear to be in cahoots with each other, to rip off homeowners who elect to install solar power systems, and who knows what phuque-all-else, the 1%ers are scheming, to start scamming us for trying to save a few bucks, because they want control of our lives. .think not? , check out_what the KOCH Bros. , are doing to the economy and working class people, like you and me, and our families! ! Time for a drastic change in the way we do business with sellers, buyes and hier-ers because they’re

  3. Ricardo Teamor says:

    Those are pretty huge numbers in terms of savings but how how upfornt payment? That is also quite big and what is the certainity that the numbers predicted above are accurate? I don’t think that Sunroof will ever be able to give an accurate estimate. Do you think so?

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