And I imagine 25 years from now, the new solar roof be cheaper and more efficient.

Prying the old tiles off of the ruins of an post-apocalyptic wasteland can be very cost efficient.

It also makes sense to use freely available slave labour.

25 years is just what they guarantee, it probably lasts much longer.

My solar roof (not Tesla, of course) is meanwhile 21 years old, and works almost like on day 1. Since I dont expect a sudden failure in 4 years, my guess it that it will last another 10-20 years.

For the record, I had 4x some small panels (165W) from a reputable company that shall remain nameless. They had a 10 year warranty.

Turns out that (a) the 10 year warranty actually meant "generating at least 90% of rated capacity in full sun after 10 years, but pro-rated across 10 years if not" and (b) they fell under this level after less than 5 years.

This is what I'm curious about. There seem to be really large differences between panels. Got two 150W panels for 78€ each this year. Peak output so far was around 240W, if performance stays like that for about five years I might break even in about 5 years for the full setup.

What leads you to believe a solar roof will last "much longer" than 25 years?

>Since I dont expect a sudden failure in 4 years, my guess it that it will last another 10-20 years.

Oh, you're just guessing.

Bear in mind that most residential roofs (of any sort) only last 10-20 years anyhow.