This article could have easily been called “Why Florida Residents Won’t Drive Solar Electric Cars.” That’s not to say that we won’t one day drive cars with some kind of energy storage (batteries) that is recharged by the sun. It’s just that we won’t be charging the battery using solar power generated on the roof of the car.

Theoretically, we should be able to build a battery with adequate capacity that is light and small enough to suit an electric car that meets our expectations, and that’s the direction in which I think we are heading. The problem with solar energy is that it is highly variable in nature, not particularly predictable on a short-term scale, and requires a large surface area to produce much energy.

You might be asking, “What about efficiency improvements?”

Today’s commercially viable solar panels top out at around 20% efficiency, meaning that they can convert about 20% of the sunlight hitting a given area on the earth’s surface to electricity. Just for grins, let’s assume that one day we will reach 100% efficiency with photovoltaic technology, and be able to convert 100% of the sun’s energy into electricity for a given area. Here are some generous assumptions we can make for some basic calculations:

• 1,400 watts per square meter hits the earths surface.
• 100% of the sun’s energy in a given area can be converted to usable energy to propel the vehicle.
• Southwest Florida gets the equivalent of approximately 6 sun-hours per day on average.
• The vehicle is about 7′ wide by 15′ long, or about 10 square meters.
• We can cover the vehicle 100% with solar panels.
• The panels are mounted at an optimal tilt angle regardless of what direction the vehicle is travelling.
• We never drive or park in shade.
• The battery technology has no efficiency losses – 100% of the solar power goes into the battery, and 100% is usable.
• No other electrical needs (lights, air conditioning, etc.)

If all of these outlandish assumptions were true, we could generate 84 kilowatt-hours of usable electricity on the average day (not the worst rainy day, mind you). How far and how fast would that 84 kilowatt-hours get you? Today’s Nissan Leaf  can get around 250 miles on 84 kilowatt-hours of energy according to the EPA! Sounds good, right?

Future cars could improve on aerodynamic drag, weight, and friction, and increase the range quite a bit. Sounds even better, right? Before we get too far, let’s remember that we are dealing with some crazy-generous assumptions.

With today’s photovoltaic technology, a reasonable estimate for actual solar energy production on a 10 square meter vehicle would be  closer to 8 kilowatt-hours. Even if batteries were 100% efficient and the Nissan Leaf became 4 times more efficient, that would still only move the car about 100 miles a day on solar power mounted on the vehicle.

Get to the Point!

There will be tremendous improvements in vehicle, battery, and solar electric efficiency in the future – perhaps the near future. The point is that the amount of solar energy hitting a small moving target on the earth’s surface is simply not enough to get the distance and performance demanded for the transportation needs of the vast majority of us, even in Southwest Florida where sunshine is abundant. The physics behind solar powered cars does not point to a practical solution.

Ultimately, I do think we will all be driving mostly electrically propelled cars. There will be improvements in vehicle design and battery efficiency. The source of the energy required to “fuel” our vehicles may very well be solar. Roof and ground mounted solar can provide the required energy for electric vehicles today. However,  solar mounted on the vehicle of the future, if any, will provide only a nominal amount of the energy needed for our vehicles.

Are there reasons to explore vehicle-mounted solar panels? Absolutely! There are some applications where this could be very beneficial, like short-distance travel vehicles or where there is no readily accessible fuel or charging source. Solar on vehicles could extend range some amount or power accessories in the vehicle. Solar energy and the future of electric vehicles are intertwined, but not the way that you may have thought or hoped.