Winter driving and hypermiling tips for electric car owners

It's winter and even though global warming is making our winters a bit warmer each year, it is still cold out which affects all kinds of vehicles. Because electric cars are not driven by a gasoline powered furnace, hence they do not have a ready on-board heat source, cold weather is a tricky issue because the cold decreases the effectiveness of batteries, and generating heat to warm the passengers takes away energy that could be used to drive the vehicle. Not to worry because there are a few bits of simple advice courtesy of the MyNissanLeaf discussion board.

The first factoid is that batteries are chemical devices, storing electricity in carefully designed chemical reactions, and it's a matter of simple physics that chemical reactions slow down in colder temperatures. It has to do with the rate of vibration at the molecular level at different ambient temperatures. This is an issue that affects not only electric car owners, but gasoline car owners as well are experienced with the car battery or engine fluids freezing up and being unable to start the engine. In extreme climates the common practice is to plug in an engine block heaters to ensure you can start the car, and perhaps someone is working on just such an accessory for electric cars.

Cold weather has an effect to decrease the energy you can draw out of a battery, but it appears to be a matter of debate just how profound that effect is. It's best to assume your range will be a bit less than it normally would be.

Coda Automotive's sedan has an active thermal management system to keep the battery at optimal temperature, even while parked. The system both heats or cools the battery depending on ambient temperature, because operation at high temperature is also a bad idea. Effectively what Coda has done is build the equivalent of an engine block heater (or cooler) into the car. In theory it means the Coda sedan will not see a range degradation in cold weather, while the other electric cars will.

There are two issues with low temperatures. One is the effect on battery pack capacity we just discussed, the other is the creature comfort of the passengers. Typically we just turn up the heater in the cabin, but this isn't recommended in an electric car. Gasoline engines are extremely inefficient with a ton of excess waste heat that conveniently can be used in the winter to heat the car for creature comfort. Electric cars do not have this convenient heat source, and heating the cabin means powering up some kind of heating coil. The Nissan Leaf has a more efficient seat heating system, in addition to the cabin heating system. Turning off the cabin heating system will reduce energy consumption, leaving more of it available for driving. One member of the MyNissanLeaf forum says if he turns on the cabin heater range drops by 10%, but using the seat and steering wheel heaters does not affect range.

Another tip is to "preheat" the car while it's still plugged in for 5-10 minutes before driving. Preheating the car still uses energy out of the battery pack, but because it's plugged in the charging system will automatically top up the battery as energy is drawn by the heating system. Meaning you get your creature comfort without comfort impacting driving range.

Unfortunately you may be unable to pull off this preheat while plugged in trick while at the office, if you do not have access to a power connection.

Hypermiling techniques are also as useful to extend electric car range, as they were to extend gas car range in 2007-8 when all the talk was on high gasoline prices. For example, rather than keep your foot on the accelerator until the last minute then slam on the brakes to stop for a red light, see off in the distance the light has turned to yellow or red, and ease off the accelerator, letting your car gently coast to the intersection. In other words, coasting to a stop makes better use of the momentum already in the car than does slamming on the brakes. Similarly do gentle accelerations from a stop, rather than lead-footing it. The dashboard information systems will guide you in developing efficient driving techniques.

Consider the difference between mechanical and regenerative braking. Mechanical braking simply removes inertia and momentum from your car to make it slow down, but does nothing to store that energy anywhere to reuse it in a moment when its time to speed back up. Regenerative braking attempts to turn some of the energy into electricity, to recharge the battery pack a bit. There is debate on just how useful regenerative braking actually is. By coasting to a stop it means you're not throwing away the inertia and momentum already moving the car, but it also means your brake lights are not on, and you're not informing the people behind you of your intentions.

On the Mitsubishi i-MiEV the regenerative braking system is adjustable to have a very light or very heavy effect, with the heavy regen setting acting a lot like the engine braking effect in a standard transmission gas powered car or motorcycle.

For further discussion see: Any tips for cold weather driving

About the reporter: After 22 years in Silicon Valley's software industry David Herron is now writing about green transportation (electric vehicles) from Silicon Valley. He also runs the popular electric vehicle discussion forum, visforvoltage.org, and is the author of the book "Node Web Development".