No company has built a business more singularly around the goal of sustainability than Elon Musk’s Tesla Motors (TSLA). That was true during the decade he’s spent promoting the development of commercially viable electric cars, with a goal of bringing them to the mass market. And it’s even more so now, with Tesla’s recently completed acquisition of SolarCity (SCTY), the solar-panel company run by his cousin, where Musk is the largest shareholder. Among the companies’ aims: To develop batteries for storing solar-generated power, solving a problem that has dogged clean-energy advocates.

Much remains to be done, starting with generating profits. While building gorgeous luxury cars, Tesla’s also faced safety concerns and struggled to meet production goals, even before confronting its promised five-fold leap to 500,000 cars a year in 2018, with the forthcoming introduction of its $35,000 Model 3 sedan. Yet Tesla’s offered proof that the automotive future doesn’t need to run on gasoline, and taken real steps to turn that vision into reality. Far-bigger rivals are now rushing to follow.

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A version of this article appears in Fortune’s September 1 issue as part of the Fortune Change the World list, our annual ranking of major companies whose business activities are having a positive social impact. Click here to see the entire package.