I am considering solar panels, and I have some trees in the neighbor's yard immediately to the south of my house. What's a relatively accurate way to estimate annual electrical production from a given kW solar panel system that considers shade from the trees? I have gotten estimates from different installers, and they are both lacking in detail (I'm not sure if it considered the trees at all). Regardless, I would feel more confident in a third party tool or service to estimate production.

I have tried Project Sunroof, but I am not sure how recent their data is as it relates to the height of the trees.

  • How much and how heavy of shade do the trees give to your roof? Heavy dark shade on most of the for most of the day, probably less than 5% of production. Light shade on 10% of the roof for an hour, will probably not lose much.
    – crip659
    Commented Jul 24, 2022 at 21:31

1 Answer 1


I'd start out by taking pictures of your roof every half hour or so and scale them to get an accurate figure on how much sun hits your roof on a daily basis and where to place the panels. You'll have to get some historic information on your yearly days of sunshine to figure out the yearly sunshine. Then throw in your number of panels and the output per panel. This is how we used to do stuff before the internet.. :-)

  • 1
    There was a before the internet? Mouth hangs open in awe and wonderment...
    – FreeMan
    Commented Jul 25, 2022 at 12:44
  • Nice idea. Is there an independent vendor I can hire to do this for me? I'm not confident I'd be doing the math right. If so, what are these sorts of vendors called so that I know what to search for? I could have a solar installer do this, but that seems like an obvious conflict of interest if they're trying to sell me panels.
    – Mike Eng
    Commented Aug 11, 2022 at 2:39
  • @MikeEng The problem is most "solar consultants and engineers" are associated with installation companies so you're right back where you started.
    – JACK
    Commented Aug 11, 2022 at 23:31

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