EV Range in Cold Weather



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Sunday February 10, 2019 EV Range in Cold Weather - I just read an article by Paul A. Eisenstein on the CNBC website talking about the loss in range of battery electric vehicles in cold weather.  There has been a number of such articles over the past couple of weeks as low temperatures across the US have set records.

For those of us who have driven electric for some time this drop in range doesn't surprise us at all.  I will let you in on a little secret, high temperatures affect range too, and both high and low temperatures also impact the range of ICE vehicles.  It becomes more apparent on an Plug-in vehicle because you track range closely most of the time.  On an ICE vehicle you usually look at the fuel gage and see if you need to fill up but on a plug-in you typically what the estimate of range that the car produces.

I drive a plug-in hybrid and if I switch on the A/C I immediately see a drop in range, usually by about 10%.  If I turn off the A/C the range will pop back up again.  That's because the software that estimates the range takes the power draw of the AC into consideration.  On a typical ICE vehicle the fuel gage measures the amount of liquid in the tank so you are totally oblivious to the fact that the A/C being on means you are using more fuel to travel the same distance.

Heat is a little different. The ICE vehicle has an advantage in the heat department.  One of the reasons that ICE vehicles are so inefficient is that the combustion process produces lots and lots of waste heat.  You can tap into that waste heat to warm up your car.  This doesn't come without a penalty.  The more heat you remove from the engine coolant the lower the engine efficiency becomes and again this impacts fuel economy, though much less than using an electric heater does in an EV.  Some Plug-in Hybrids like my Prius Plug-in will turn on the ICE to get heat rather than use a second source of heating.

On older EVs the solution was to install battery warmers so that the batteries were kept warm even as temperatures outside were below freezing.  In some very cold areas a similar thing is done with ICE vehicles where the car can be plugged in overnight so that block heaters can prevent the coolant in the engine from freezing.  Modern EVs like Tesla provide preconditioning.  In cold weather the car can be warmed up using external power if it is connected to external power.  In this case when you get out to your car it is already warmed up and if you have a short commute you might not even need to turn on the heater.

The range of the EV is also impacted by the temperature.  Modern Lithium Ion batteries perform best at temperatures between 70 and 80 Fahrenheit, which is about the same temperature span that humans prefer.  Lower or hotter temperatures reduce the efficiency of the batteries and impacts range.

There are other factors that also impact range including wet weather.  Tires are designed to channel water away so that the rubber meets drier pavement.  This also takes energy as does running lights and windscreen wipers.  These factors also have an impact on the fuel economy of an ICE car.  Even running the radio will create a draw on the batteries but, at least on my car, the difference has been too low for me to measure.

The big question we need to ask is "how does this affect me?"  Obviously if I am driving a PHEV it just means I may burn more gas when it's cold out.  BEV drivers the situation is a bit different depending on if you are driving close to the limits of your battery's range or if you are just driving shorter distances.  Let me give you some examples.

A Nissan Leaf with an 80 mile electric range may only get 72 miles if cold temperatures cause range to drop by 10%.  If a round trip commute is equal to an average US commute of 32 miles then the loss of range is not going to pose any problems.  In fact my range could drop as much as 50% and I could still make my round trip commute..

But lets say my round trip commute is 72 miles.  In this case I would be right at my maximum range and as a safety net I would probably need to take a charge, preferably at work, before returning home.  I may be able to drive slower each way to stretch range but it would be risky.

Lets consider the case where someone drives a Chevy Bolt on a 300 mile road trip in cold weather.  The EPA range on the Bolt is 238 miles but driven aggressively on long freeway runs it is unlikely that you would see that sort of range.  In a test done by the Washington Post they only managed to get 140 miles of range from the car under these conditions.  Journalists usually drive really hard so I am going to assume here that the driver who is going to try and do the 40 mile trip will drive more conservatively and will manage about 165 miles of range.

This would require one stop for charging on the trip but the car would have needed one stop anyway.  The impact of the cold weather is twofold.  First the driver needs to be sure that there is a fast charger very close to half way distance on the trip.  If not the trip will require two stops.  The second impact is that there is a need for a full, or close to full charge at the stop and this means that charge times would be longer, especially since the Bolt charges slower as the batteries reach charge levels above 50%.  If I was doing the trip I would probably plan on two charging stops in really cold weather.

There are lessons to be learned here.  The first one is that if you live in a climate that gets really cold or really hot, you need to make adjustments on what EV you are going to buy.  You have to be aware that the weather can have quite a huge impact on range and plan accordingly.  For a typical commuter vehicle I would recommend a range that is at least high enough to accommodate you commute using no more than 60% charge. 


The second lesson is that in cold or hot weather you may want to slow down.  While the EPA range estimate is a good predictor of how far you can drive on a full charge the local weather and your driving technique, can eat into that range.  When considering an EV you should figure out your driving style and select a car accordingly.  You should also be ready to adjust your driving style to match weather conditions.  If you drive with a lead foot and regularly get well below the EPA mpg values for your car you will probably get the same results in an EV.  The high torque at zero mph can be exhilarating and hard to resist. 


When buying an EV I recommend planning for the worst case rather than blindly using the EPA range numbers.  adjust your range expectations depending on local weather and on your driving style can make sure you make the right choice and avoid all that range anxiety.

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