Maybe there is room for another way of comparing electric cars.
We liked the format of the X-Prize competition because competitions are inherently fair: cars ran in the same conditions and energy consumption was measured by a clear metric, MPGe, so there was no cherry-picking numbers or conditions. For example, the efficiency events were run on a closed track without altitude gain or loss, and the energy used was very carefully measured by competent and impartial judges. Under MPGe the energy consumed by vehicles with diesel, ethanol, electric or hybrid drives is referenced to the energy contained in a gallon of gasoline.
But the problem with MPGe is that you have to explain it all the time. For all the X Prize Foundation’s efforts, and the EPA’s, and the Department of Energy’s (they all use and promote the MPGe metric) it’s just not that easy to understand.
But the other day Edison2’s engineering staff were asked a sensible question about our new electric model: how long does it take to charge? Our short answer was, “quickly enough to be acceptable and viable for most people” and, as you would expect, there was a longer answer as well. Real-life charging time depends on how far you go and how fast you go. Of course that’s true of all cars but it’s energy not spent on pushing a heavy car with ordinary aerodynamics that really counts. So, as we like to do, we ran the numbers.
Some of our early blog posts explained our coastdown figures, which are derived using a recognized SAE standard and measure total resistance to motion caused by aerodynamic drag, rolling resistance and mechanical losses. The VLC’s coastdown numbers are the best ever for a 4-seat car and therefore our energy consumption, regardless of energy source, is also the lowest ever.
That’s a bold statement but the problem lies in getting its significance out in an easy-to-understand way. How about how long to recharge after driving a certain distance and speed?
Our performance projections for our electric VLC model take into account a little higher rolling resistance than the X-Prize competition cars (because the batteries make it heavier) and allow for 84% total efficiency through the charger, batteries and electric motor, a figure we think is realistic. On that basis, the electric VLC will take slightly under 4 hours 30 minutes to recharge from a standard 110 Volt 15 Amp socket after a 100 mile run at 70 mph.
To put that in perspective, neither the Nissan Leaf nor the Chevy Volt can actually go 100 miles at 70 mph before their batteries go flat. In fact, the EPA rates the Leaf at a 73 mile range and Nissan concedes it takes 20 hours to recharge from a 110 V socket. Also according to the EPA, the Chevy Volt will go 35 miles on its battery and Chevy says it will then take 10 hours to recharge.
So, 100 miles for 4 ½ hours of charging, 73 miles for 20 hours or 35 miles for 10 hours. You make the call.