Cold Weather EVs

Is your new Clarity Plug In (Hybrid or EV) not getting the EPA estimated range of 47 miles for the hybrid or 89 miles for the EV?  If you live in an area in the US experiencing below average temperatures, you can probably look to heater usage.

A quick note specific to the Clarity PHEV/EV: The middle gauge on the car is the battery charge level, the left gauge on the PHEV (Right on EV) is the estimated range vs the EPA range.  This isn’t a state of charge gauge as it might appear at first.  It simply states that based on current driving, my estimated range is only 27 miles even with a fully charged battery.  This was when the high temps were around 0F.

So why does an EV do worse than a gas car?  A typical gas engine car has around 25% thermal efficiency.  What does that even mean?  Besides being very energy inefficient, it means that for every 1 gallon of gas burned, only 1/4 of the energy is going to power the car.  The other 3/4 is lost as heat, about half of that is lost out the exhaust pipe, and the other half is captured by the coolant in the engine.  This is the heat that can be used to heat the cabin, and essentially for free.

An electric car has no built in “free” heater, and has to use electric heat.  This can come in the form of a heat pump that runs the AC “backwards” to draw heat energy from the environment to heat the cabin or from a resistance heater that acts somewhat like the heating coil in your oven.  Both of these take a massive amount of power.  Heat pumps are more efficient around 20 or 30 F and resistance heat is required around 0F and less.

So what does this have to do with your range?  An electric resistance heater can draw up to 7 or 8 kw of power.  To put this in perspective, this is about the same power the main electric motors will use in the car cruising at low speeds.  It takes a massive amount of power to heat a car when you aren’t using the “Free” engine heat.

If the heater is drawing 8 kw, it can drain a 12 kwh battery in about 1.5 hours.  Just the heater.  This would mean every 10 minutes the heater would use about 1.3 kwh of battery.  This is a lot of power, and it isn’t going to move the car.

The heater in the Clarity seems to be a heat pump, which is more efficient at warmer temperatures.  It probably draws up to 3 kw (I haven’t measure this, so I could be wrong, Honda doesn’t advertise the capabilities of the heater).  Still, this means 0.5 kwh every 10 minutes of heater use.

What does this work out to in reality?  If you drive 35 miles in 60 mins, you might use up to 3 kwh for the heater, which amounts to maybe 12 miles of range.  In other words, your range would be about 35 instead of 47.  It is slightly more complicated than this, as cold batteries aren’t as efficient as warm ones, so that will result in some range loss as well.

My point is, it is normal to lose between 25% and 50% electric range depending on temperature and heater in the vehicle, as well as if the battery has a heater or not.  A car with a heater for the battery might not lose as much EV range, but will draw power from the wall to heat the battery.  For example, on very cold nights, my Volt might draw 2 kwh over night to keep the battery warm.  The Clarity PHEV (US Model) does not have a battery heater so won’t draw from the wall unless it is charging or pre-conditioning.

As an EV shopper you need to buy extra range in cold climates.  A minimum of 2x your expected range, but 3x or 4x might make you more comfortable and account for any aging losses if you own the car 10 years or more.