# Improper Tesla Roof Impact testing



## Owism (May 11, 2017)

I'm not mechie but I have enough physics and structures course education to see the impact test for the tesla roof panels is flawed due to the orientation of the panel compared to the "traditional panel" they are comparing the strength to. If they stood the tesla roof panel vertical, then it would flex more thus causing more chance of cracking I assume. Any input?

I love the concept of beautiful solar roof, I always hated the way the panels look on someones roof, that ugly look does not give curbside appeal. Can't wait until I can buy one but my roof is only 10 years old, I can wait another 10.

heres the link to the impact test https://www.tesla.com/ns_videos/Hail_3up_Smooth_h264.m4v?20170509a , its on the main page: https://www.tesla.com/solarroof


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## J_MEC (May 11, 2017)

Actually Owism, I think the way they are testing it makes the Tesla glass weaker and standing it vertical would make it stronger.

I drew a couple of diagrams and my reasoning is that if you think about the panel as a simply supported beam bending will likely be the failure mode. Bending stress is inversely proportional to the area moment of inertia. The area moment of inertia for a rectangle is the vertical dimension (b) times the thickness of the panel (h) cubed divided by 12. If you decrease the vertical dimension (b), moment of inertia goes down, bending stress goes up. You can also see that failure occured along the centerline of the center panel. This makes sense because theoretically, that is where the bending moment is the highest according to my diagrams.

Intuitively, I think this makes sense because to me thinking about standing on that panel as the vertical dimension (b) shrank down to zero would make me quite nervous, so I would rather stand on the longer one.

View attachment 9455


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## Owism (May 11, 2017)

Thank you. Yes your basic statics of materials does make sense.

Another question: Do roofing tiles have the same strength in both horizontal and vertical directions?  Is there any "direction of grain" factor which adds strength to the tile in either direction?

I know this is the least of my worries if putting up this type of roof but my main worry would be how they would mount the glass panel onto the roof?


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