Wednesday, January 12, 2022

Battery Usage While Stuck

 


The recent incident with hundreds of cars stuck on I-95 in Virginia during the snowstorm has raised a lot of questions regarding EV vs ICE vehicles - what happens if you're stuck like that in an EV? Won't the battery die quickly if you have to use the HVAC to stay warm?

The short answer is that you'd probably be better off in an EV than a gas-powered vehicle, assuming to have similar level of energy available to power the car. That is, you can't compare an ICE vehicle with, say 3/4 of a tank of gas to an EV with, say, 20% of charge. But assuming both have a similar percentage of their total tank/battery filled, the EV is actually better.

The main reason for this has to do with the engine and motor, respectively, of the ICE vehicle and the EV. The engine in an ICE vehicle is CONSTANTLY running (let's put aside those stop/start systems for a second) - when you start the car until you turn it off. Idle, high-speed, city driving - the engine is always using gas. With an EV, OTOH, the motor(s) is only using energy from the main high-voltage battery when the car is moving under power - that is, accelerating or maintaining speed. Unlike an ICE vehicle, when you remove your foot from the accelerator, the motors do not use energy and actually, through regenerative braking, put some energy back into the battery. So, the major source of energy usage for an EV, the motor, is basically using zero energy when you are stopped. 

So take the situation down in Virginia a couple of weeks ago. You have an ICE vehicle and an EV sitting side-by-side on the highway. The ICE vehicle is idling to keep the heat running - and therefore using gas (and also polluting but that's another story). The EV's motor is using no energy. Depending on the car and the HVAC settings, some energy is used to heat the car, but so little that it could literally take days to deplete the battery from a high state of charge to the point where you'd start to get concerned. This is especially true if you have an EV (like a later Tesla) that has a heat pump. They use less energy from the battery to heat the cabin, just like the heat pump in a home. See the Texas power outage in February 2021 as a great example - here is a link to just one story that discusses how people used their Teslas (in their garage) to survive - 

https://electrek.co/2021/03/05/electric-cars-texas-blackout/

How about a personal example? On Tuesday, my wife had oral surgery and due to Covid regulations I could not wait in the office (I didn't want to anyway). The temperature outside was 19 degrees. I waited for slightly over 2 hours in my car, the heat was set at 70 degrees and I had the seat heater on (probably overkill). I was also watching YouTube videos on the car's screen. My battery SOC went from 81% to 79% in that time frame. Extrapolating that, I could have sat there for another 79 hours before my battery would reach a 0% SOC! And I could extend that time period by lowering the temperature, or turning the heat off altogether and just using the seat heaters. Realistically, when the sun went down, the car would use some energy to keep the battery warm, so 79 hours is probably unrealistic. But the point is that the EV has several advantages over an ICE vehicle that MUST run to provide heat to the cabin.

Ok, so how long can an ICE car idle and provide some heat? Here is an interesting article that can help you calculate for your particular vehicle. 

https://www.autotrader.ca/newsfeatures/20190201/how-long-can-you-stay-warm-on-a-tank-of-gas/

The main example they use - a Ford Explorer - comes out to about 33 hours on a full tank of gas. You can certainly extend that by shutting off the car from time to time, but you'd have no cabin heat and when you restart, the engine is now cold and therefor less efficient. Just like in the EV, you can certainly use the heated seats - but now they are running off of the 12v battery, which you need to restart the car. And you don't want to use the radio when the car is off, as it would further deplete the 12v battery. 

So, the bottom line is that being in an EV might actually be a better choice if you're stuck in a storm. You should certainly take the precautions you would with an ICE vehicle - make sure you have sufficient fuel if you're traveling during inclement weather, have a safety kit, etc. But don't sweat it out in your Tesla, ID.4, Mustang Mach-E or whatever. Just make sure to offer a warm space to those stuck in their gas cars. 😃






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