In the video they demonstrated the tile by dropping kettle bells on them. They've definitely thought of hail.

Did you see the announcement video? They dropped a kettlebell on it and all it got was a small crack.

Now think about what will happen after water makes its way into that crack and goes through a few hundred freeze-thaw cycles.

So this technology is useless because years of wear and tear will make you need to replace the roof eventually? Isn't that pretty normal for any house?

Texas resident here. There's a guy who's been riding a Segway around my neighborhood looking for weather damage from recent storms, and his pitch to homeowners is that they don't need to replace the entire roof, just the section where things are--or will soon be--leaking.

It's probably more efficient to replace the entire roof at once, and insurers would almost certainly prefer the entire roof to be the same age, but asphalt does have some advantages for situations in which nearly every storm tears up just a few shingles.

Isn't there a significant difference between a kettle bell and golf ball sized hail?

I think the right question is why are roofs not already made out of high-impact glass? Did nobody ever think about this before Elon? Maybe.

More likely a glass roof is a net negative that has to be offset by the solar cells, making them less cost effective than otherwise.

Yes, yes they are... they are far more durable than their counterparts. Remember there are may types of glass, including 'bullet proof glass'.

Isn't it more cost effective to put some sort of transparent shield on top, for those places with above-average risk of hail damage?

or is it that such a cover gets dirty and not-so-transparent faster than the original top layer?

I'm guessing this must be something already being considered, so what am I missing?

Metal roofs are pretty hardy, but sound like a paint can full of ball-bearings even in light hail or heavy rain.

Asphalt roofs are inexpensive. Given that hail-damaged asphalt roofs keep getting replaced with asphalt roofs, I have to think it's some kind of market/regulation/short-term-profit thing.