EV Range: KiloWatt Hours Rather than Gallons

Don B
Don B
Jul 30, 2017 · 4 min read

Thank you for reading my series about exploring America with an electric vehicle. If you’re interested in purchasing a Tesla, contact me for a referral code, which entitles you to $1,000 off the purchase price and free supercharging for as long as you own the vehicle. See all posts in this series at the GAMR 2017 tag.

“How many gallons of gas does the tank hold” is a common question someone might ask when evaluating a car they want to purchase. If they are active road trippers, they will likely look for a vehicle with a large gas tank, so they have lots of range. It is not uncommon for ICE (internal combustion engine) vehicles to have a range of 300 to 500 miles through a combination of gas tank size and overall efficiency (MPG).

Battery Electric Vehicles have batteries, not gas tanks. The equivalent of gas tank size in a BEV is the size of the battery, measured in kilowatt hours (kWh). Kilowatts is the amount of power a battery or motor can generate and hours is the amount of capacity the battery has to sustain that power. My Model S has a battery rated at 85 kWh. In its simplest form, that means my battery could maintain an output of 1 kW for 85 hours or 85 kW for 1 hour.

For an EV to be road trip capable, it requires a battery size of at least 60 kWh in my view, which should net a range greater than 200 miles. I refer you once again to InsideEVs excellent comparison chart that lists key specifications of each electric vehicle on the market, including the vehicle’s battery capacity and EPA rated range.

In practice, many factors govern the range of a given vehicle (regular car or BEV) including temperature, wind, weight, road conditions such as rain or snow, elevation change, etc. However, Tesla, in particular, has done an excellent job averaging all of these variables. Except in the most extreme conditions (e.g. minus ten Fahrenheit weather), I get pretty close to the rated range or usually a bit better.

The EPA rates my Model S at 265 miles of range, which equates .3207 kW/mile (85 kW/265 miles). Lenny’s displays show this number in Wh/mile, so just move the decimal three places: 320.7 Wh/mile. However, Tesla uses 270 Wh/mile as their benchmark, so any number lower than 270 and I’m doing better and anything higher, worse. I use Lenny’s trip odometers as a simple tool to see how I’m doing on average. Below is Lenny’s trip odometers for the Great American Road Trip 2017 so far.

Lenny’s energy use has been remarkably consistent this trip. Even yesterday with the laps around the Indianapolis Motor Speedway, air conditioning on, and lots of stop and go driving, we’ve averaged 275 Wh/mile.

The chart below shows Lenny’s energy display while we were crossing the Shenandoah mountains. The vertical access is energy use in Wh/Mile, and the horizontal access is miles (in this case the past 30 miles traveled). The higher the peak, the steeper the climb. The deep trough in green means the Lenny is recovering energy and storing it in the battery. In technical terms, Lenny is turning kinetic energy into potential energy. In a fossil fuel vehicle, the driver would be losing that energy to heat as they use their brakes to keep the car under the speed limit. The chart also shows the average energy used (265 Wh/Mile) and remaining range on the right (159 miles in this case) assuming the average remained at 265 Wh/mile.

What I can tell you is that once an EV has a rated range greater than 250 miles, you don’t spend much time thinking about the issue. We charged to 100% when we arrived in Indianapolis for the Midwest Tesla Gathering and drove 122 miles over the next 36 hours including some aggressive acceleration on the Indianapolis Motor Speedway. We still have more than 120 miles of range remaining. Since it is only 65 miles to the next Supercharger in Lafayette, Indiana, we’ll just depart directly from our hotel and head straight to the next Supercharger.

On Friday night, Tesla delivered the first 30 production Model 3 EVs to customers. They emphasized during this event that they intend to stop talking about battery size and only talk instead about range. They said people have found the technical terms confusing and I guess they’ve gained enough confidence in their ability to measure range, that they can hide the technical jargon. I’m willing to bet some of these efficiency numbers will still be available on the Model 3’s center display, but from a marketing perspective, you will only hear them talk about Model 3 range in miles. You will not find any reference to battery size on Tesla’s Model 3 page.

If Tesla’s approach works, future EV buyers (other than enthusiasts) may never know anything about their battery size, capacity, or performance, which, if you think about it, isn’t all that different from today’s automobile market. Think about how few people know anything about how their vehicle works under the hood.

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