There are natural synergies between the solar and electric vehicle industries, and right now, we're just scratching the surface of how they'll work together. Tesla Motors (TSLA -0.33%) and SolarCity have partnered to bring solar power to electric vehicle charging, and they've also used electric batteries as energy storage for solar installations. Yesterday, I highlighted how researchers in the industry are looking at using EVs for storage for the grid.

Today, the two made another big step forward when Ford (F -0.67%) announced the C-Max Solar Energi Concept, a solar-powered vehicle that moves fueling from the plug to the roof.

Source: Ford Motor Company.

This is the first major automaker to use solar panels to charge its vehicle and allow drivers to go off-grid. 

How C-Max Solar Energi works
Ford's C-Max concept has 300 watts of SunPower (SPWR) solar cells of the roof, slightly less than a single solar panel. From an operating perspective, the solar panels are almost unnoticeable by the vehicle owner. They passively charge the battery, requiring less plug-in time, but that's about it.

SunPower is a natural choice for the auto industry because its 24% efficient cells are the most efficient on the market and will generate about 50% more power than a conventional cell. Its cells are also thinner than those of competitors, allowing them to be flexed to contour to a roof's shape. Similar cells have been used to power solar aircraft, boats, and small research-based cars.

300 watts worth of solar cells won't charge the 21-mile electric range of the C-Max Solar Energi in a single day, but it improves the attractiveness of going electric. If we use the much larger battery of a Tesla Model S to look at long-term potential, the 85 kW-hr battery gets an EPA estimated 265 miles in range and would require 283 hours of full power to fully charge the battery. If we assume 6 hours of optimal charging per day, that's about 47 days of charging for a full charge.

That may not sound like a lot, but consider that it's enough to charge a Model S enough to drive about 2,048 miles per year. That's about 12% of what the average person drives in a year. Imagine saving 12% every time you fill up with gas, just for having solar cells on your roof.

What's the potential?
In my opinion, this is just the start of ties between solar and auto manufacturing. There's no reason why every EV shouldn't have solar cells, and the rooftop is just the beginning. If we add the hood and trunk to areas used for charging, we may see 1,000 watts of solar on a single vehicle, and 5,000 miles of annual solar range isn't far off.

For SunPower, 1,000 watts of solar cells put on 1 million cars per year at $2 per watt is $2 billion in potential revenue. That's almost half of what the company expects this year.

We're years, or even a decade, away from EVs being that big a market, but you can see the potential. That's why this concept car is such a big deal for both Ford and SunPower. We're just scratching the surface of the potential for solar and EVs, and a decade from now, we may not only put the gas station in obsoletion, the electric plug may not be a necessity, either.