100 Questions about Electric Vehicles

By David Herron

Last Update: August 24, 2018

Every kind of vehicle has a limited range based on stored energy it carries on board. Gasoline vehicles carry only so many gallons of gasoline, limiting the driving range, and electric vehicles carry only so many kiloWatt-hours, again limiting the driving range. This question as written contains an embedded assumption that electric vehicles are limited while other kinds of vehicles are not.

The general way to describe driving range is:

range = energy stored / energy consumed per mile

Battery pack size, or for that matter gasoline tank size, is the primary determiner of driving range. It's a simple equation: Divide the energy stored on the vehicle by the energy consumption per mile, and you have the driving range. (See Energy storage, energy consumption, weather and electric car driving range)

Here's two concrete ways to correlate energy storage, energy consumption, and range.

range = gallons gasoline / gallons consumed per mile
range = kiloWatt-hours / kWh consumed per mile

These are of course rule-of-thumb calculations. Someone driving aggresively with a lead foot will consume more energy per mile, and therefore get less range. It does not matter whether you're driving a gasoline or electric vehicle, physics is what dictates that result.

Put another way -- an electric car will often support driving 4 miles per kiloWatt-hour. Therefore a 24 kiloWatt-hour car might give 100 miles of range. But, the Nissan Leaf when it had a 24 kiloWatt-hour pack was only rated for 75 miles of range. What gives?

The manufacturers design electric vehicles to prevent consuming the last electron in the pack. Bringing a battery pack to have no remaining electricity will damage the pack. Therefore electric cars are designed to hold some energy in reserve.

To avoid the risk of battery damage, some electric vehicles are designed to start warning the driver when the charge is running low. The Kia Soul EV starts bugging the driver at 20 miles remaining range to find a charging station soon.

Secondly, the official range estimate is calculated by using an EPA testing protocol. The calculation earlier is way too simplistic to do anything more than get you in the right ballpark. The EPA test is a much better estimate of likely driving range. It is based on a variety of speeds simulating a combination of city driving and highway driving. (See How does EPA estimate electric car driving range?)

About the Author(s)

David Herron : David Herron is a writer and software engineer focusing on the wise use of technology. He is especially interested in clean energy technologies like solar power, wind power, and electric cars. David worked for nearly 30 years in Silicon Valley on software ranging from electronic mail systems, to video streaming, to the Java programming language, and has published several books on Node.js programming and electric vehicles.
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