Is My Roof Right?

Determining whether solar makes sense…

Using Google Maps to get Started

Instead of going up on your roof, you can get started by using the internet. I’m using Google maps; the site is http://maps.google.com/.

Let’s first look at my roof. If you type in 222 Cleveland Ave. Mill Valley, CA, you should see something like this:

If you’re looking at a map, switch to “Satellite” by selecting that option in the upper right.

Then use the drag-bar on the left to zoom in closer, and closer.

I’m the lower of these two homes. And yes — as you can see, I already have solar.

Let’s see what we can learn, just by looking at this Google satellite image:

  1. I now know which direction’s south, since Google orients its maps with north up, south down.
  2. Note there’s lots of “stuff” on my roof — particularly my main roof, in the center. What you’re seeing are skylights, plumbing vents, furnace vents, attic vents, etc. Roofers call these penetrations. Penetrations are bad for solar, since panels can’t be placed where penetrations are. Another big problem with penetrations: they cast shadows, and even small shadows really ruin solar production (more on this later). But our purpose was to see if there’s room for solar, and clearly there was.
  3. While my roof is clearly getting a lot of sun, I can tell from the shadow from my neighbor’s one large penetration (top of image) that the sun was east of us when this picture was taken, meaning that it’s morning. You can probably tell from the image that our houses are built on a hill that faces east, and it’s clear that there are lots of trees. Is my roof getting good sun at 2 in the afternoon? What about during the winter, when the sun is lower? You can’t tell these important details from this picture.

In fairness, the plan wasn’t to solve everything by using Google maps. It was to get us started.

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