Three major factors contributed to making solar as viable as it is now, none of which Solar City invented (but it is executing on them better).
1. Germany basically subsidizing China (and others) to build the massive solar panel production pipeline it has now that are producing ridiculously cheap panels[1].
2. Financial innovation to allow consumers and installers to pay for panels over time (PPA, leases, loans, etc.). These were originally pioneered by SunEdison[2], and the industry has been innovating on them since (including SolarCity with its MyPower Loan).
3. The California Solar Initiative[3] and Department of Energy's Sunshot Initiative[4]. Both were incredibly well designed to gradually wean solar off of subsidies and foster innovation through strategic grants, and they have worked incredibly well at teaching the solar industry to stand on its own two feet. We are well on our way to $1/watt[5].
SolarCity has executed incredibly well in this industry, so they definitely deserve tons of credit for installing so much solar. But it's a disservice to the rest of the companies, governments, and financiers to say they invented the recent growth. Everyone, including SolarCity, has come together to build a mature and exponentially growing industry that was 1 out of every 78 jobs last year.
[1]: http://qz.com/41166/how-germanys-energy-transformation-has-t...
[2]: http://archive.onearth.org/article/selling-the-sun
[3]: http://www.gosolarcalifornia.ca.gov/csi/index.php
[4]: http://energy.gov/eere/sunshot/sunshot-initiative
[5]: http://cleantechnica.com/2015/07/10/price-solar-hits-record-...