Its solar installations during each of the last two quarters were the two lowest in at least five years, and the company has gone from being the undisputed market leader to the No. 3 installer. While deployments in the third quarter were stronger than the second-quarter’s five-year low, the company has a long way to go to rebuild its presence in the solar energy market.

Musk said part of that decline was intentional. Tesla’s solar energy business was losing money and draining cash from the company at a time when it needed every penny it could muster to launch its Model 3 electric vehicle – a less expensive sedan that Musk views as the key to Tesla’s survival. So Tesla diverted resources from the solar business and channeled them into the Model 3.

At the same time, Tesla took a unique approach to cutting costs by pushing its solar energy sales online and streamlining its offerings into a small number of standardized products. That made a big dent in how much Tesla is spending to acquire solar energy customers – the biggest expense solar firms face.

But it still is unclear how comfortable consumers will be going online to make a purchase as big and as important as a solar roof, although online sales also are a big part of Tesla's electric vehicle business.

Solar roofs are expensive