Finishing the buyout of Solar City, Tesla's CEO Elon Musk set his sights on selling a new kind of roof made of solar panels, even though they already exist.

"It's not something on the roof - it is the roof," Musk told a group of Wall Street analysts during a call last week to discuss quarterly earnings. "Which is a quite difficult engineering challenge and not something that is available anywhere else."

Quickly searching the internet, solar roofs, as Musk envisions them, have been around for more than a decade and are already in their second generation with two variations: one that integrates with asphalt roof shingles and one with tile roofs. Both variations are different from the traditional, solar panel attached to the roof. A format that usually requires building a new roof that can support the weight of the panels.

If solar roofs already exist, why is Elon Musk "really very excited" about selling solar roofs?

First, Musk's vision for the future has been captivating us all for years. He took the electric car that was once seen as a hippy dream-mobile and turned it into a luxury you'd be crazy not to want. Now he's turning they bulky solar panels into something way more desirable.

Secondly, one of the major producers of the shingle design solar roofs just shipped its last order, leaving an untapped market for Musk to fill. With 5 million new roofs being built every year in the U.S., there are lots of potential costumers. Solar City is promising a lifetime of 30 years for their solar roofs, ensuring everyone replacing their roof should make the shift.