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Back in August, Ford announced that it would enter into a partnership with solar panel firm SunPower to help 2012 Ford Focus Electric owners install photovoltaic solar panels on their houses, which could let them power their cars from solar energy.
Called “Drive Green For Life”, the scheme entitles Ford’s Focus Electric customers to a massive discount on the purchase and installation costs of a 2.5-kilowatt peak photovoltaic solar panel array.
The idea, of course, is that the solar panels generate electricity to charge the car during the day -- or to offset any electricity used at night to charge the car, by feeding power back to the grid where possible.
As is often the case with the Internet, however, we’ve seen a rather amusing twist to this story. Some websites have claimed that the 2012 Ford Focus Electric will come complete with a 2.5-kilowatt solar array mounted on its roof.
Oh, dear.
It’s the traditional chain of Chinese whispers: One website prints an inaccurate story, then gets cited by another, before the claim is transformed into an even more inaccurate story. The chain may continue until there are very few real facts left.
Take the most recent reiteration of this story. Completely confused about the facts, one site actually says that the solar panels will provide enough energy to propel the car along without needing to plug it in.
“This means being able to drive longer distances without having to stop and recharge your car,” the author claims. “It also conserves energy by relying on solar power to help propel the car along, therefore using less of the power contained within the cars’ battery.”
Err... No.
For a start, even with today’s modern solar cell technology, a 2.5-kW system normally takes up from 130 to 200 square feet of space - far more than the roof area of any car on the roads today.
Secondly, even if you could fit it onto a car, such a large solar array would dramatically increase the car’s weight and its aerodynamic drag, leading to much reduced performance and economy.
To emphasize the point, a Ford spokesperson confirmed to us earlier today that the SunPower solar cells are meant for your home, not your car: “Otherwise all our aerodynamic improvements would be useless”.
But perhaps the funniest part of this story for us is the idea that an electric car -- fully laden with heavy solar cells, five passengers and a full trunk -- could actually drive at freeway speeds on just 2.5 kilowatts of power per hour.
For the record, the EPA’s official efficiency consumption for the similarly sized 2012 Nissan Leaf is 35 kilowatt-hours per 100 miles -- or 350 watt-hours per mile.
In other words, that’s equivalent to around 7 miles of travel per hour’s worth of solar energy. We think you’ll agree the math just doesn’t add up.
Of course, the SunPower home-based photovoltaic system will be an ideal way to offset the electricity you need to charge your electric car when you’re at home. And it will provide clean, renewable energy for your home when your car isn’t plugged in.
But if you want a car with solar panels that exclusively power the car without depleting its battery pack, your search will lead you to something a little less practical and a whole lot more expensive than a 2012 Ford Focus hatchback.
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But, I don't agree with the assertion that solar panels on cars are totally impractical. A smaller array could be useful and could be integrated into a car's roof without increasing the aerodynamic drag or any significant weight increase . A solar panel could easily add 2 kW of energy back into the battery daily while your car sits in your employer's parking lot. Leave your car at the airport when on vacation and come back to a car full of free "fuel"!
Mean solar radiation is about 600 watts per square meter, peak efficiency is less than 20% for a solar panel you will find on a car. If you can get 8 hours of that per day, you are doing well. I don't think you can get more than say a half square meter of panel on the roof of a Focus. So here's the math:
600 x 0.2 x 8 x 0.5 = 0.48 kilo watt hours per day.
Figuring 90% charging efficiency, you are looking at about 2 months to charge a car with a solar panel. Or less than 2 miles per day of driving from the solar panel.
Also, 10% shade on a modern solar panel drops the output by maybe 50%, since the cells are in series.
Have you ever tried to find a shady spot in a parking lot? They aren't common outside of garages.
I appreciate what you're saying but I think you underestimate the real estate available on the average car roof. The Fisker Karma has a 120 watt panel integrated into a modest sized roof. Also, I believe 10 hours of charging per day is possible for a lot of people.
120 x 10 = 1.2 kW per day
Other EV's could have solar panels for less than many of the less useful options offered on cars today.
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