You can think of a Tesla, to a gross approximation, as a giant battery with some wheels strapped on. Giant batteries are more than anything else crucial to the

You can think of a Tesla, to a gross approximation, as a giant battery with some wheels strapped on. Giant batteries are more than anything else crucial to their business and what they spend a lot of time figuring out how to manufacture well. That's why they've gone into the business of selling batteries for temporarily powering homes or letting people store solar energy. And once you're in the business of selling solar storage batteries it makes some sense to integrate with a solar provider. But I think you're right in your second paragraph and it might make more sense for Solar City to just be a re-seller of Tesla batteries without Tesla buying them.