From time to time, I get an inquiry on this blog about the possible benefit of putting solar panels on an electric car to recharge the batteries while it is not being driven. Let’s face it, your typical vehicle, electric or not, spends most of its time turned off, sitting in the open. And, I tell my inquirers that the short answer to their question is “No” and in most cases, it just is not worth it.
If they want the long answer, I explain that solar panels, at their present stage of development, are simply are not as efficient as internal combustion engines, and electric cars do use a substantial amount of electrical energy to move themselves about.
Doing The Math
Let me illustrate: the average home-converted electric automobile consumes approximately 300 Wh (watt-hours) in the process of going one mile. A watt-hour is a measure of the electricity used in a specific amount of time, in this case, one hour. This enables one to think of electricity in terms of a discrete unit.
One might think of a watt-hour as like a cupful of electricity. If it takes 300 watt-hours to travel a single mile, then let’s calculate how much a good-sized solar panel could contribute to replenishment of that energy.
Let’s say we installed one of those 4-foot (1.2 meter) behemoths on the roof of our car. A really efficient one on a brilliantly sunlit day could push out close to 150 watts. That translates, over the space of an hour, to 150 Wh (150 watts/hour). Am I making sense so far?
Okay, in order to move your car one mile, you need to provide it with 300 Wh, and for the solar panel to charge your batteries with 300 Wh, it has to be exposed to sunshine for an uninterrupted period of two hours, at least.
Here’s the math: 150 Wh x 2 hours = 300 Wh. Or, using our analogy, 1 hour in sunlight = 150 cups of generated electricity, and 2 hours in sunlight = 300 cups of generated electricity, and your car needs 300 cups for each mile it goes. Thus, if you want to drive your electric car five miles, your single 150-watt-ouptut solar panel would need to sit in the sun for ten hours total (you need a total of 1500 Wh, or 10 x 150 Wh).
You might get the sort of weather you need to do this in Australia or California, but there are plenty of areas where it would be unusual to see ten hours of sunlight in a month. That is why the solar-powered cars you’ve seen on television scurrying around the Australian Outback are all built very light, very low-profile, and literally blanketed in costly solar panels.
Despite the heroic “coverage,” and the intense Aussie sunshine, they are only able to manage about 62 mph (100 km/h) intermittently. Car companies are still interested in the use of solar panels to augment the power supply for their electric models, particularly in their sunnier markets, to offset the drain from AC, stereos, and other accessories.
However, panels are still not efficient enough to recharge an electric car’s 16,000 Wh battery pack – unless, of course, you can afford to let your car sit in the sun for a month between uses!
I sincerely hope that this adequately explicates the limitations of what a typical solar panel can generate for its dimensions, and why shops that convert standard cars to electric are adverse to advising their customers to shell out a lot of money for such a small return.
Might as well foot the $800 bill for household electricity, instead- after all, that expenditure, at today’s price of electricity, will allow you to operate most electric cars for two years, at the very least!
DIY Electric Car Conversion Guide
Are you planning to convert a conventional automobile into a pure electric car in your home garage? If you are, it is best you read up on the science of EV conversion.
Before you begin your conversion project, check out the Convert2EV ebook by Les and Jane Oke. The Okes live a green lifestyle in Canada and one way of keeping their carbon footprint small is by using pure electric car. The Convert2EV manual was written based on their experience of retrofitting old gas guzzler into electric vehicle.