Long vs Short Trips in an Electric Vehicle

AKA How not to end up stranded on the side of the road!

Turns out…range estimates go out the window with mostly highway miles! For the first three weeks I had an electric vehicle, I only ever went a few miles at a time. It was fun and easy and I didn’t fret about charging. But finally it came time to take some longer trips. And with them, some new lessons I want to share with you! Read on for more of my lessons in electrification.

A journey that started off with the car reporting 141 miles of range…98 miles later the battery is nearly empty!

When I got this EV, the data from the first ~5,000 miles suggested that the car got 4.2 miles/kWh. The car has a 60 kWh “tank” (battery), so that equates to a range of 252 miles. Not bad and fairly in line with my expectations for a ~240 miles range.

Baked into that range calculation are lots of assumptions. One of which relates to the fact that all EVs seem to all be equipped with a technology that the Toyota Prius made fairly mainstream over 20 years ago — regenerative breaking. That is, when you apply the breaks, you actually recharge the batteries. This is pretty freaking brilliant, given that in most cars, you take all the energy you spent to accelerate and when you break you just turn it into heat (aka waste…braking actually uses 46% of the useful energy of a fossil-fuel vehicle!!!). With regenerative breaking, you capture the energy and get to reuse it. You basically run the process of accelerating in reverse — instead of using battery energy to spin a motor to turn into increased velocity for the vehicle, you reduce the velocity to put energy back in the battery. Awe…some!

As I drove back from Santa Cruz today, I saw this play out in real life. There were so many turns and miles of downhill that over the course of about 25 miles, the estimated range on the car went UP by 20 miles! But…then I hit the highway and the opposite effect kicked in and that’s what I want to talk about in this post.

During highway driving, there are consistent high speeds, providing little of the benefits of regenerative breaking. I found that the 4.2 miles/kwh average the car reported plummeted with highway driving. Adding just one 100 miles journey after 5k miles, the average went down to 4.1! That first 100 mile journey came in at just 2.86 miles/kwh (32% less range/kwh than the average of the first 5k miles!) and used half the total battery capacity.

Ok, so i MIGHT have been messing around with the “sport mode” and seeing what the car could do, knowing that I would be able to charge it up on the other end and not needing to worry about how much was left. That’s just one scenario…but it may explain why on the way back to SF, I got 3.6 miles/kwh :). That’s only only 14% less than the original average mileage.

Again, due to not awesome metric availability, I can’t report all the trips in the same way. The cleanest reporting is if a trip is made from a full battery charge…then I can determine exactly how many miles/kwh resulted. However, getting a full charge without a dedicated charging spot is tough, so in various cases I have to resort to approximations from the car’s unsatisfactory data points. However, for home charging, I have added my Kill-A-Watt meter into the equation, so I can at least make an accurate calculation of the energy delivered to the car.

So…it seems that the ~240 mile expected range is closer to 190 miles with mostly highway. That’s a big wake up call! More to report on this soon.

PS. If you have topics you want to hear more about on going electric, please add a comment!