Ever since electric vehicles (EVs) became a viable alternative to traditional gasoline cars, there has been a push to make them greener. Rather than fueling EVs with electricity from the grid -- which is powered mostly by coal and natural gas -- nearly every major EV maker has a partnership to pair their vehicles with rooftop solar energy. Tesla (NASDAQ:TSLA) even bought SolarCity to make the integration of solar and EVs seamless. 

Ultimately, the goal will be for EVs to generate some of their power themselves. Yes, the sun could provide electricity that could power your vehicle -- and solar cars may be closer than you think

Ford C-Max Solar Energi concept car with a solar roof.

Image source: Ford.

Solar-powered cars are on the horizon

Today, Audi is taking a stab at solar power for its electric vehicles with a recent partnership with Hanergy subsidiary Alta Devices. The company makes high-efficiency thin-film solar cells that have been used on satellites and electric-powered aircraft in the past. To give an example of potential energy production, Alta says that a Hanergy Solar Car could have 1,092 watts of solar cells and generate 5.59 kWh of energy per day. In other words, a 310-mile range Tesla Model 3 could get about 23 miles of range per day from the sun alone. 

If Audi and Alta Devices are able to make a solar roof work on a car, it could become a viable option for more than just Audi. Every major EV maker would seek out its own solar option for EVs because it would become a huge selling point. 

This isn't the first solar on cars concept we've heard of. Solar on production EVs first became a concept in 2014, when Ford (NYSE:F) built the C-Max Solar Energy concept car with SunPower (NASDAQ:SPWR) solar cells integrated into the roof. In theory, the car could generate about 2,048 miles of charge per year with the solar cells on the car, and if you added cells to the front hood and trunk, it may have been able to get to 5,000 miles of self-supplied range. However, since then we've heard very little about Ford or SunPower bringing this concept car to market. 

Solar-powered Model 3? 

These aren't the only solar/EV projects taking place, either. Tesla CEO Elon Musk has hinted that the Model 3 could include a solar option before long. In November 2016, Musk said that solar would be an option for the vehicle, although we haven't heard anything about the solar paneled option since. Given Musk's ability to push Tesla into new technologies and his desire to provide clean energy for its vehicles, I wouldn't be surprised if Tesla is the first to make the solar car a reality at scale, even if it hasn't announced anything yet. 

Solar cars are a matter of time

It's not really a question of if solar energy will make its way onto electric vehicles, it's a question of how and when. SunPower tried to use its solar cells on a car because they're flexible, but a silicon cell may not make the most sense long term because there's a limit to how flexible a silicon solar cell can be and it needs to be installed like a tile.

It's likely that a thin film or coating of some sort that's built directly into the body components will make more sense than silicon solar cells. This would allow solar to adapt to the car's body or roof's contours rather than the body having to conform to the limited flexibility of solar cells.

No matter what technology is used, if the auto and solar industries can fully integrate solar onto vehicles, it would be a free energy source that could generate thousands of miles worth of power each year. With companies like Ford, SunPower, Audi, Hanergy, and Tesla working on the problem, the hope is that this technology may not be very far away.

Travis Hoium owns shares of Ford and SunPower. The Motley Fool owns shares of and recommends Ford and Tesla. The Motley Fool has a disclosure policy.