Sunday, December 04, 2011

Baby, It's Cold Outside

Haven't updated on the Leaf recently. Sparkii continues to plug along, doing duty as our primary vehicle. He takes my wife to work, my son to school, all of us to the store. Power consumption is beginning to climb as the temperature begins to drop. Here's a chart showing how driving range has varied with temperature over the past 11 months:

So what's going on? Is the cold affecting the battery? Are EVs a failure in freezing temperatures? Not really. Thinking outside the box just a bit, cold storage facilities use electric forklifts. And it gets a lot colder inside a meat locker (-35C) than it does around here. So what is it? It's the heater:

Internal combustion engines are notoriously inefficient. Only 20-25% of the energy from gasoline goes into moving the car forward. The rest is turned into heat. As I'm fond of saying, "gas engines are an 80% efficient furnace that provide locomotion as a by-product".

Not so with electric motors, I'm afraid. On the plus side, a typical electric motor converts 90% of input energy into motion. On the minus side, there is almost no waste heat to keep us comfortable on frosty mornings. So we have to dip into our precious stored electrical energy to heat the car. You can see from the chart above that as the temperature has dropped, our accessory (non-motor) consumption has climbed from the low single-digits to nearly 25% of the total.

Still, I prefer having an efficient electric motor and being in control of our energy/comfort trade-off. We can always follow President Carter's advice and put on a sweater.

No comments: