[panick21_]

I don't think it was clear that it would be out compete on price or performance. If you compare roof + solor to solar roof, the idea was that eventually it would compete with doing both separately.

I'm also not sure if its actually worse on longevity.

[oliwarner]

It seems fairly clear if you consider a 50-100 year roof (ours is 150 years, and it's only had membrane changes in that time) against a 25 year roof.

I'm sure the steel shingle will last a fair time but if the PV elements need replacing four times a century, that's not a non-trivial cost.

When my PV panels die, it's just £400 a panel, four hex bolts and some quick connectors to replace it. It's no contest.