But I also think he did really believe in electric cars and solar power

Musk is very good at separating wealthy investors from their money. Said investors are not entirely stupid - but Musk has historically been very skilled at cultivating a perception that he's going to do something revolutionary that will change the world and make his investors rich, if only investors would give him money. You know, that he can colonise mars, build fully self-driving (on motorways) cars by 2015, and build a practical LA to SF hyperloop.

To con investors he was an amazing futurist, there needed to be a grain of truth mixed in there, even if there were other significant logical gaps in his claims. I don't believe he genuinely cared about the planet or other people, but he did see (as many people were, in fact, already screaming) that change was coming and decide he could sell it to investors and enrich himself.

Pretending to be an amazing engineer and to care was his modus operandi for a long time - perhaps the most notable incident was in the 2018 Tham Luang cave incident in Thailand; Musk pledged to put engineers on inventing a submarine to rescue them. When Tesla's design was unlikely to work, but a heroic team of divers rescued the children, instead of expressing relief the children were safe, Musk labelled the rescuer a 'pedo', showing that he never really cared and it was just a stunt.