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Articles on Electric Vehicles

June 25, 2018
Paul Gipe

Energy Consumption Estimators, Trip Planners, and the Chevy Bolt EV


We leased a Chevy Bolt EV (electric vehicle) in November 2017. Since then we've taken the car on several road trips of varying distances. Based on these trips, I've tested the accuracy of three different estimators or trip planners: EV Trip Planner (EVTP), GreenRace, and Chevy's Energy Assist app for the Bolt.

Driving an EV--even in EV friendly California--isn't as easy as just hopping in a conventional vehicle and taking off. Where we go and the routes we take often don't have charge stations--of any kind.

Consequently, planning is essential. Part of that planning is knowing how much electricity a trip will take and whether you will have enough to reach your destination and return. And if not, where you can charge and how much you will need to charge when you do. As Tony Williams of QuickCharge Power likes to say, "Plan the drive and drive the plan."

Denizens of various forums (mynissanleaf.com, mychevybolt.com, chevybolt.org) have directed me to these estimators over the several years we've been driving electric. EV Trip Planner and Green Race calculate how much energy, in kWh, a trip will take. (Tesla has a reliable estimator built into each car.) The Energy Assist app works differently.

Chevy's app presents the results of its trip planning function as a percentage of the Bolt's traction battery capacity remaining. If you started with a fully-charged battery, the app returns the percentage of the battery's state-of-charge (SOC) remaining after you reached your destination. For example, if the app indicates you have 80% remaining, you've used 20%. To find the number of kWh the app calculates that you need to reach your destination, you need to know the kWh stored in the battery when you started off.

The Bolt has a nominal capacity of 60 kWh. Only GM knows how much useable capacity any one of its Bolts actually has. There's no consensus among users on how many kWh you have to work with in a Bolt that's fully charged. For the comparisons here, I used the car's nominal capacity to calculate the number of kWh based on the app's estimate of the charge remaining. Note, "your performance may vary."

The Bolt is our only car and as such we'd like to use it for all trips by car in California. Even in mid-2017 there are places in California we'd like to drive the Bolt where there are no charge stations--except those for Tesla of course. Thus, we need to know with some degree of confidence that we can get to our destination.

Altogether, I've driven eight routes in the Chevy Bolt since we leased it. Most routes include several legs. On some routes I've been able to compare the Bolt's consumption to that of the Nissan Leaf we previously leased. (See Bakersfield to Ridgecrest Revisited in a Chevy Bolt.)

In short, no one estimator is 100% accurate. The Chevy app appears best and can be used while you're on the road. That's a big plus. However, there are trip legs where the app underestimated the amount of energy (kWh) needed by 10% to 20%. That's a lot when you're at the edge of the Bolt's range. You may need 4 kWh to 5 kWh more than Chevy's app estimates you will need. And you may not have those kWh on board if your battery's capacity is less than the nominal 60 kWh GM says you have to work with.

Wind Possibly a Factor

In the cases where the Energy Assist app's estimate are off most dramatically, I've checked the estimates several times and I get the same results. Wind could have played a factor. Several of the routes with the largest errors crossed mountain passes that are notoriously windy.

Two of the routes (Bakersfield to Cantil and Bakersfield to Tehachapi) are through the Tehachapi Pass and wind through the pass could have been a factor. However, the direction of the error is not representative of what you'd expect with the prevailing westerly winds through the pass. Winds could have been off the desert during both trips and that does occur. I haven't looked into it further.

Similarly, the routes through the Tejon Pass (Bakersfield to Silverlake and Bakersfield to LAX) could have been affected by the wind. In both cases through the Tejon Pass the estimates were affected in a manner that would reflect the normal wind patterns. That is, a tailwind through the pass and a headwind returning to Bakersfield. Thus, the trip would use less energy to Los Angeles with a tailwind and more returning against a headwind than that estimated.

Similarly, there's one trip over the Temblor Range from Grover Beach to Bakersfield that could have been affected by a headwind. For this trip, the app underestimated consumption by 18%. In a subsequent trip from San Luis Obispo to Bakersfield, the app underestimated consumption by 9%.

GreenRace's estimate for the 30 kWh Leaf is also useful. It's closer to our driving experience in the Bolt than GreenRace's estimates for the Bolt itself.

EV Trip Planner's estimate for the Nissan Leaf (α version) is the most conservative of the three. It overestimates the kWh needed for a specific leg from 20% to 30%.

In none of these cases was A/C or battery conditioning a factor. Summer's now here and the Bolt display reports the percentage of charge used for climate control and battery conditioning. I am now monitoring these conditions as well.

Chevy's App Useful on the Road

Chevy's Energy Assist goes an important step further than the two web-based programs. Most importantly, you can take it with you and use it on the road. The app will also map the route and include when and how much you need to charge. The app then offers you several charging options along the route. You can pick the location you want and it gives you the amount of charge you need and the time it will take.

The app also reports the station's rated power, and the number of chargers at the site. Unfortunately, the app designers are confused between the rated amps of the charge station and its rating in kW. I checked two EVgo stations and the app reported both as 120 kW when EVgo reports that they are 120 amp or 50 kW stations.

I also couldn't find any way to save the routes in the app for future reference.

Summary

Using any of these estimators remains preferable over simply relying on the Bolt's internal range estimate, notably when crossing one of the state's mountain ranges. However, until California's charging infrastructure is further developed, it remains wise to plan conservatively, especially when driving at the edge of the Bolt's range.


 

 


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