"SolarCity" ...city... “People do not understand the magnitude of the business," Musk said. "Solar will be the single largest source of electricity generation".
I was talking about Elon’s overall portfolio, of which Tesla and SpaceX are both examples. But if you’re specifically curious about Tesla, I’d point out that Tesla’s mission was to give everybody an electric car, and they decided to start from ~“make a crazy fast electric sports car” and go from there. Along the way, some ancillary nebulous goals ~“also become experts in building our own batteries” and ~”also solar for everybody’s homes”.
Good question, but my first thought was to ask what is nebulous about this project. It has clearly stated goals and Toyota has identified tech and capital.