Elon Musk and Tesla Motors (TSLA -2.04%) have slowly been leaking information about their future product plans, and what emerged last week might be a bigger deal than most people think. After introducing the solar roof with SolarCity (SCTY.DL), Musk said Tesla had built a glass-research group that had helped make the solar roof possible. Speculation soon went to Tesla putting solar panels in the roof of a Tesla vehicle, which Musk ended by confirming that solar on the Model 3 will probably be an option in the future. 

This wouldn't be the first solar roof in a vehicle. SunPower (SPWR 31.27%) and Ford (F -2.05%) made the C-Max Solar Energi concept car in 2014 to bring solar and EVs together. But the product never really moved past the concept phase, so Musk could be the first one to bring solar car roofs into production.

The potential for EVs and solar energy

The amount of energy a car can generate from the sun is more significant than you might think. The C-Max Solar Energi has 300 watts' worth of solar cells, which I calculated could potentially provide enough power to drive a Model S 2,048 miles per year, assuming optimal charging conditions. A smaller Model 3 could potentially get 2,500 miles of charge -- or more if the solar cells covered more surface area. 

These figures are assuming six hours of direct sunlight, which is probably a stretch in reality, but the potential is there for a vehicle to charge itself for a significant driving range in a year. And Musk appears ready to push forward with the technology. 

The roof of Ford's C-Max Solar Energi. Image source: Ford.

Manufacturing may be a bigger challenge for solar EVs

What's not yet known is how Tesla could turn a good solar EV concept into a reality in manufacturing. SunPower's cells hold a natural advantage because of their back-contact construction, making them flexible to the curves of a roof surface. Since Tesla and SolarCity haven't said much about what their solar cells are going to look like, we don't know if they'll have the same flexibility -- or what the efficiency of a cell will be. 

Making the curved glass roof with embedded solar cells wouldn't be easy, either. And even if Tesla can do it, it may be costly for customers and, more important, would take resources away from other Model 3 developments. If the Model 3 is going to be successful, it will be because it's a great vehicle that's manufactured at a low cost, not because the car has a solar roof option. 

Solar roofs are cool, but they could be a distraction

There's no question solar roofs on cars are possible -- or that they would be a great option for Tesla to eventually offer. The questions are more around whether or not now is the right time to put the resources into developing such a product. 

Tesla is already working to acquire SolarCity, integrate solar sales into Tesla stores, develop solar roofs, and build out a solar manufacturing plant in Buffalo, New York. Oh yeah, and Tesla is trying to manufacture cars, too. 

That's a lot for one company to have on its plate -- especially a company burning billions of dollars as it builds out capacity. I love the idea of solar roofs on vehicles, and I think they'll be a standard feature someday. But right now may not be the best time for Tesla to put resources into a feature that won't be a key to making the Model 3 a success.