Why did it fail? I remember seeing the launch announcement for SolarCity and being wowed (logic: every house needs a roof, so why not make the roof from solar tiles instead of regular tiles and get free energy).

I guess the unit-economics didn’t work? (but seems like a good thing to have tried given the massive TAM)

Solar Roof was vaporware when it was presented by Musk. It was blatant fraud. There's no "free energy" here. The roof was way more expensive than a regular roof covered in solar panels.