My father in law sold solar in the 70s. His take is that it failed for the same reason it fails today. For most consumers in most environments, it makes no economic sense whatsoever, even with tax incentives. The short total lifespan, rapid aging of the cells, expensive maintenance, and risks of roof damage over time, altogether reveal costs that typically are not advertised but remain obvious to most consumers. That's aside from the unsightly appearance of the cells. In environments with more expensive power grids and higher temperatures they appear to be a suitable economic solution for the consumer. E.g. Phoenix, AZ.