Electric Vehicles seem to be the future of ground transportation so I thought I would share some of my experiences with driving an EV. This installment will address the issue of range.
It appears almost a certainty that electric vehicles (EVs), are the future of ground transportation, because they are touted to be much friendlier to the environment than internal combustion engine (ICE) vehicles. That may appear to be a somewhat controversial conclusion as some people point to the polluting effects of mining the lithium required for lithium‐ion batteries. This is a valid point, but let us not forget the horrendous environmental impacts that have taken place in the course of drilling for, pumping, transporting and refining fossil fuels for cars. Remember the Exxon Valdez and Deep Water Horizon incidences, both of which were environmental catastrophes. But those are just really the tip of the iceberg, when looking at the impact on the environment caused by the petroleum and coal industries over the last century.
In any case, I thought it would be beneficial to share my experience in driving an electric vehicle. There is much to say about the difference between driving an electric vehicle and an internal combustion engine vehicle, so in this installment I will discuss the one aspect that seems to be the most concerning for those
unfamiliar with EVs. One of the first things that comes to mind and is one of the first questions that I am asked when I talk about my electric vehicle is, what is the range, how far can you go?
The answer is, it’s complicated. On my vehicle the fuel meter, if you will, looks like a battery and next to it there’s a number which indicates a number of miles left to drive with that particular battery state of charge. I drive a Tesla Model 3, Long Range (bigger battery), which indicates a range of 300 miles when
fully charged. That number is just nominal in the sense that it is really an indication of how far you can go driving at a particular speed and under certain conditions, just like the EPA mileage rating of an ICE car.
Several factors enter into the actual mileage one can expect from a given state of charge; city vs highway driving, speed at which you are driving, acceleration rate, topography (hilly vs flat terrain), temperature
and auxiliary system use. I find it an interesting sign of the times that my wife’s ICE car has a computer display that shows the gasoline used, in gallons per hour, of things such as the A/C, heated seats, etc.
Let’s first look at the impact of cruising speed on fuel mileage. Any vehicle that travels through the atmosphere experiences a drag force on it which is proportional to the square of the i t s velocity, so if you
double the speed you’re going to quadruple the drag force that must be overcome by the engine or electric motor driving it. This results in a greater rate of consumption of the fuel, be it gasoline or battery power. But for someone driving a typical ICE vehicle this is not a huge concern because gas stations are so ubiquitous that one is rarely very far away and you can stop and refuel rather quickly. This is not true for the electric vehicle. Charging stations are further apart and it takes longer to charge the battery than the few minutes it might take to fill a gas tank with fuel. What this means for the driver of an EV is that they develop a different mindset when it comes to their fuel level. I rarely let my battery level get very low. When I’m not on a trip I have relatively small concern for the battery level at any particular time. However if at the end of the day, the battery gets down to around 50% I will typically plug in the charger in the evening before retiring and let the car charge up to about 90% overnight. I only fully charge the battery when preparing to go on a trip.
I have a 240V outlet in my garage which allows the vehicle to be charged at a rate of approximately 30 mph so if I’m down, say, 60 miles from my 90% target it will take around two hours for it to charge. I have it set up so the charging normally starts at 10 PM when the electric rates are a little bit lower and it automatically stops at the level for which I have it set. When I know I’m going to go on a trip then I set it for 100%.
When I do go on a trip, I have to plan for possible charging stops if I don’t have adequate range to reach my
destination. For my particular car the navigation system does this for me. I put in the destination; it tells me if I can get there and what level of battery charge I will arrive at my destination with. If I cannot make it without stopping to recharge, the navigation system will indicate where and for how long I should stop to recharge during the trip.
I typically spend 15 to 20 minutes during a recharge stop on a trip outside the local area. Charging an EV is different than refueling your gasoline car. The gas tank is just an empty vessel that provides little resistance to the inflow of the gasoline. The battery is different, as you increase the charge on the battery, you’re basically shoving electrons to one end of the battery. Remember from high school physics, like charges repel one another, so each new electron being shoved into that battery is experiencing an ever‐increasing repulsive force. Thus the rate of charge starts out relatively high and then tapers off as the battery reaches its capacity. Realizing this, Tesla cleverly installed a network across the country of what they call superchargers, these stations are capable of charging a car’s battery very rapidly with high voltage DC. The charge rate may start out at something like 500 mph being shoved into that battery and then it tapers off near the end of the charge to maybe 100 mph. So, the whole process may take something like 20 minutes or so depending on the state of charge when you first plug‐in and what final charge level you want (I don’t always charge to the maximum level). Tesla was also very clever in positioning these supercharging stations near facilities which provide refreshments, restrooms, and possibly some entertainment within walking distance. Typically, on a trip I will drive 200 miles in about 3 to 3 1/2 hours before I stop to recharge. That’s actually a good distance to go before stopping. I get out of the car, go inside use the restroom, have something to drink or eat and come back to the car. A few minutes later I can depart refreshed and ready to go. That’s not a bad scenario unless you’re in a real hurry to get somewhere.
When I’m driving in the local area, I charge the car at home and pay the local electric rate. We’re relatively fortunate to have somewhat lower rates than many areas. I figure driving locally, charging at home, it cost me about two cents a mile to drive the car. When I go on a trip however, and stop at a Tesla Supercharger I pay the local electric rate in that area as well as a surcharge for using their service so this could bring the cost per mile up to near 10 cents per mile and that is getting close to the cost of driving a gasoline car at today’s gas rates.
As opposed to the ICE car, an EV does better, in terms of fuel efficiency, in town than on the highway. That is because during all the stop and go traffic in town, every time I slow down I am putting some energy back into the battery due to regenerative braking (the motor that was driving the car now becomes a generator charging the battery). Regenerative braking also tends to smooth out the effects of hills on range. When an EV goes downhill, even coming partially off the accelerator can result in some charge being put back into the battery, where as an ICE car will just dissipate its kinetic and potential energies by applying the brakes to maintain speed and turn those energies into heat; all the while the engine is idling and using fuel.
So what is the bottom line on EV range? From my experience, when driving in town the displayed mileage is pretty much right on. On the highway, one really becomes aware of the physics involved as the cruise speed definitely affects the rate of battery depletion. As an example, I started with a full charge and drove 220 miles, most of it on the NYS Thruway at 75 mph and arrived at my destination with 30 miles remaining on the battery range display. This was in the warm weather and we had made one 20‐minute, non‐charging stop on the thruway, during which I left the A/C on so the cake we were transporting would not melt.
There are many more differences between the experiences of driving an EV and an ICE car and I will cover them in a future issue of the Environmental Thought.