Clean Power

Published on August 18th, 2015 | by Joshua S Hill

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Google’s ‘Project Sunroof’ Helps Homeowners Calculate Roof’s Solar Energy Potential

August 18th, 2015 by  

A new 20% project from Google labeled ‘Project Sunroof’ will provide homeowners the opportunity to calculate the possible solar energy potential of their rooftops.

Google allows its employees 20% of their paid work time to work on their own project, with the possibility that those projects will become part of the larger Google package. Carl Elkin, a volunteer with the Boston-based solar program Solarize Massachusetts and a solar homeowner himself, developed Project Sunroof, “a new online tool” that Elkin believes will “help homeowners explore whether they should go solar or not.”

The project is currently limited to the San Francisco Bay Area, Fresno (in central California), and the Boston area, and provides homeowners access to the same high-resolution aerial mapping used by Google Earth to help calculate their own roof’s solar energy potential, “without having to climb up any ladders.”

Google-3According to Elkin:

If you’re in one of our test regions, simply enter your address and Project Sunroof will crunch the numbers. It first figures out how much sunlight hits your rooftop throughout the year, taking into account factors like roof orientation, shade from trees and nearby buildings, and local weather patterns. You can also enter your typical electric bill amount to customize the results. The tool then combines all this information to estimate the amount you could potentially save with solar panels, and it can help connect you with local solar providers.

Naturally, many of Google’s 20% products enter life in a limited beta — as is the case with Project Sunroof’s limited roll-out to San Francisco, Fresno, and Boston. However, Elkin notes that “during the coming months we’ll be exploring how to make the tool better and more widely available.”


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About the Author

I'm a Christian, a nerd, a geek, and I believe that we're pretty quickly directing planet-Earth into hell in a handbasket! I also write for Fantasy Book Review (.co.uk), and can be found writing articles for a variety of other sites. Check me out at about.me for more.



  • GCO

    Interesting, nice-looking, but the data shown is just bogus.

    Yesterday, after I saw this on another site, I tried my own house. It mapped features that weren’t there, like I had some huge bump in the middle of my flat roof, and completely failed to show the shade cast by the chimney and the neighbor’s tall trees, despite such shade being clearly visible on Google’s own satellite(-like) image.

    The square footage indicated is also completely off, by a factor of ~3 in my case. It apparently considers the whole roof usable (and in the case of the neighbors, their patio too), making no attempt to account for the fact PV modules should be tilted, can’t be cut, cover vents or skylights, or the required clearances for firefighter access.

    For anyone interested in going solar: awesome, now get an installer on site. That’s the only place where everything can get looked at properly.

    That simple phone call will give you a dramatically more accurate and reliable assessment, something you can actually base a five-figure financial decision on.

  • phineasjw

    Nice tool.

    I’m in one of its areas. For a $125 monthly electric bill and a 6kW system, it’s claiming an up front cost of $18K after incentives, with a 6 year break-even point, and a $33,000 savings over 20 years. They’re baking in a 2.2% annual increase in electric rates.

    Probably optimistic numbers, but pretty eye opening nonetheless.

    • Marion Meads

      so that would be $25.7K before incentives or $4.29/Watt installed.
      Solar City is at $5.10/Watt, Sungevity at $3.99/Watt. MagicSolar offers at $3.85/Watt. SolarHome plus your local installer offers at $2.88/Watt installed before tax incentives.

      I climbed my roof and measured it, much more accurate than Google Sunroof will ever be.

      • phineasjw

        SolarHome is with purchased panels? What panels do they use?

        • Just had a chat with a friend who signed a contract with Sungevity for a 3.75 KW system for $7500 – a 20 year upfront pay lease. I think this is a pretty good deal as you do not have to take care of anything and they guarantee the output. This is as good as buying the system because I think Sungevity will not take that system out after 20 years even if you pay them.

          • Marion Meads

            That would be buying a fixed price of $0.06/kWh for everything that the panels will produce for 20 years, assuming 5 hrs equivalent full sunshine per day.

            It is one thing to buy, lease or own. I find that owning the system have some pride of ownership.

          • This scheme has a number of advantages. First, the price per watt is $2/watt which is hard to beat for such small systems even after tax breaks. There is no additional paper work for claiming the tax break as it is baked into the price. Second Sungevity guarantees the output and is responsible for maintenance and insurance. This removes minor headaches like inverter replacements, cleaning etc. Third there is no hassle in selling the house as the lease is paid for. The new owner just gets to enjoy free electricity. Finally, after 20 years the system should depreciate to a few hundred dollars. I do not think it will make financial sense for Sungevity to pay someone 4-5 hrs labor to dismantle and take away the system. They will probably offer to sell the system for less than $100 at that time. So it is as good as buying the system with no headaches. Only problem is this scheme is not offered everywhere. My friend lives in Pleasanton.

          • GCO

            The price is interesting indeed, but I think you overstate the advantages while dismissing drawbacks.

            Unlike the roof underneath, maintenance is pretty much nil on a PV system. Ditto for insurance, it’s part of the house. And no, Sungevity won’t come clean the thing, or touch it in any way, unless production falls below the probably very conservative minimum they committed to (and even then, they probably have the option to just compensate the customer for the difference, if that’s more cost-effective for them).
            Your claim that they’ll want to sell the stuff for less than 100$ in 20 years is completely unsupported. On the other hand, a lot can happen during that timeframe, which brings us to…

            Key disadvantage: the system remains Sungevity’s. The homeowner, current or future, can’t touch it. (S)He will have to go through Sungevity, paying whatever they feel like asking, for everything.
            The PV system should outlast the roof, so when time comes for some repairs or replacement for example, how much will it cost to move the PV out of the way? What if the repair is urgent but Sungevity doesn’t see it that way?

            Sorry, signing away your right to your own roof for 20 years doesn’t come without some serious strings attached (and even an unintended pun).

          • Their production guarantee is for 80% of normal output which was 1400 Kwh/KW for a string inverter system – not too bad. Whether they clean the panels or pay cash should not matter to the end customer who just wants to save on the electricity bill. I am talking normal depreciation here. With solar panels becoming cheaper every year and the install costs going down, depreciation can only be higher for existing systems. The last point is valid but once panels are put on a roof, that part of the roof gets extra protection and should be less prone to external repairs. There may be internal repair issues though. That part is unpredictable. I think the advantages outweigh the minor disadvantages here.

          • Bob_Wallace

            Would the system have any appreciable value after 20 years?

            Twenty year newer panels would likely be a lot more efficient. Demand for 20 year old panels might be pretty low.

            3.75 kW of new might cost cost as little as $1,300 ($0.35/watt). Sungevity would have to remove the panels and racks and probably do some site cleanup work (have to read the contract). Haul away and store the panels and racks. And then try to find someone who would pay enough to cover labor and sales costs. They’d have to price well under $1,300.

            I can see them asking maybe $500 to leave the system on the roof but probably settling for a lot less.

        • Marion Meads

          there are many brands to chose from. The cheapest for grid-tied system is $1.48/Watt (Replus from ReneSola), and their top of the line is HyperX2 Sunpreme for about $2.40/Watt. Local installers to install these complete system charge anywhere from $0.90-$1.29/Watt.

      • Why does a roof have to be climbed to be measured?
        That space is only for roofers with no safety gear and loud music.

        • Babam

          I also climbed our roof and using non-stretch kevlar tape, my errors are less than 1/4″ for a span of 480″. I am able to plot exactly where the chimneys and vent pipes are located.

          Yeah, the solar reps climbed the roof too.

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