It seems like even a small solar panel on the roof of an electric car would make a lot of sense. When you’re sitting at work for 8 hours, your car can just soak up some sun. I’m assuming there is some sort of problem related to cost, rather than efficiency, but I can’t figure it out.
Edit: Thanks for the help. It makes a lot of sense now. I appreciate the in-depth answers too.
In: Engineering
The cost/benefit analysis doesn’t hold up. You couldn’t put enough panels on the car to charge it in a reasonable time even in perfect conditions and the cost of adding the panels would raise the total cost of the car. So, could you? Sure. Would you alienate more buyers for virtually no extra value proposition? Absolutely.
Not really. The additional weight just wouldn’t make sense given the benefit. Even for a fairly large car, it would be fairly difficult to get more than 2-3 sq meters of solar roof (unless it gets pretty crazy). Even with the most efficient panels (and drivers willing to park in the sun all day), this would be around 3-4kWH at best. A typical fully electric car has about 60-100KWH batteries. So it would make very little difference in terms of charging a car.
First, some do. Fisker has announced an SUV that has a solar panel on the roof that they claim will get you 1,000 miles of travel over the course of a year.
The reasons that most don’t come down to cost, complexity and marketing decisions. Having that solar panel on the roof adds costs to the car that might not ever be paid back over the lifespan of the vehicle. It also adds complexity to the charging mechanism which introduces more chances for failure. Finally, people like to buy cars with sunroofs and all glass tops.
With the amount of space available for placing solar panels (ignoring weight considerations), the power output of such panels could still take days to fully charge a vehicle, even with direct sunlight for most of the day.
Typical solar panels put out around 15 watts per square foot under ideal circumstances, and at best, a typical car might only have about 20 square feet or so (a 5×4 foot rectangle or equivalent) to work with.
As a reference, the Tesla Model 3 has a minimum battery capacity of 50,000 watt hours, which translates to ~3333 [sq. Ft * hours] to fully charge (~166 hours of optimal sunlight for a 20 sq ft panel)
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