Electric car economy explained

Think fuel economy figures will soon be a thing of the past with electric vehicles? Think again, electric cars need to be efficient, too

James Wilson
Dec 13, 2019

In the world of electric cars, range and charge times dominate the headlines. Although electric motors are much cheaper to run than a petrol or diesel engine, there is still come cost invovled, and so the efficiency of these next generation cars remains a very important aspect. After all, there is no point having an electric car capable of driving 400 miles on a single charge if it uses the same amount of energy as Poland over the entirety of winter to do so.

With that in mind, it makes sense that as motorists are trying to reduce the environmental impact of travelling, the cars they are driving should be efficient in how they use electricity. Just because there are no fumes coming out of the back of electric cars doesn't mean there is no environmental impact in driving them. For now at least, the burning of fossil fuels generates most of the power used to charge these electric cars in the UK.

Similar to petrol and diesel cars, smaller electric cars with more modest performance tend to have the best economy – think cars such as the Nissan Leaf and Renault Zoe. Meanwhile larger, more luxurious models which come with greater performance, such as the Mercedes EQC, fare much worse.

Be careful not to be suckered in by an impressive looking range figure though when considering electric car economy. A bigger battery might last longer, but it could well be less efficient with its energy use than a smaller battery.

 

Electric car economy

The economy (or efficiency) of an electric car is commonly defined by how much electricity a car uses to travel a set distance. It will look something like this: 34 kWh per 100 miles or 340 Wh per mile. It is worth noting, that when it comes to units of measurement ‘per’ is often shown as a “/”, so the above could look like this: 34 kWh/100 miles or 340 Wh/mile. In the case of these units, the lower the figure, the more efficient the car is, as it uses less energy per mile.

To help keep things confusing, some manufacturers present electric car economy as how far a car can travel on a set amount of electricity. That means it would look something like this: 3 miles/kWh. Also, depending on the car manufacturer, economy may be quoted in terms of kilometres rather than miles. When this type of unit is used, the more efficient a car is, the higher the figure, as it travels further per unit of energy.

For those who didn’t know already, kWh and Wh refer to kilowatt-hour and watt-hour respectively. A kilowatt-hour is a standard quantity which represents how much energy a 1,000-watt device (could be a washing machine, could be an electric motor, could be anything in between) uses in an hour. A watt-hour is the same, but for a one-watt device. For a full breakdown of electric car jargon, take a read of our dedicated electric car jargon explainer article.

How electric car economy is calculated

In theory, electric car economy can be calculated by using a car’s battery capacity and its official range. For example, an electric car with a 40 kWh battery pack and a 100-mile range would have an economy/consumption figure of 40 kWh/100 miles. However, using this simplistic approach is more of an approximate guide, as for one reason or another, not all the battery capacity can be used to power the wheels.

So, in reality, the best way to calculate economy is to fully charge an electric car, drive it until it is flat then measure how much electricity it takes to fully recharge it. This is how official economy figures are calculated, although these are under lab conditions, so you can expect the figures to be a little optimistic compared with driving on real roads packed with stop-start traffic, hills and changeable weather.

Electric car economy, much like petrol and diesel cars, changes all the time depending on things such as road gradient, how fast you are driving, outside temperature and wind direction.

Up until now, these figures haven't always been readily available. However, as demand for electric cars grows and carmakers gain more understanding of what information the electric car market needs, economy figures should become easier to track down.

Good and bad electric car economy

It's still very early days for electric cars, but we are beginning to get an idea, with the current crop of cars at least, what constitutes a good level of efficiency. It is worth noting that the values below are based on official WLTP range figures, i.e. those found under test conditions.

In reality, cars will typically achieve lower economy figures than those found under WLTP testing procedures, but the only way to have economy figures that you can compare is by having a test which is the same for all - i.e. in a controlled environment, so at least they will all be slightly ambitious.

ScoreEconomy figures
Wh/mileWh/kmkWh/100 mileskWh/100 kmMiles/kWh
Excellent190-225118-14019-2312-145.0+
Good226-260141-16124-2615-164.0-4.9
So so261-295162-18327-3017-183.0-3.9
Might as well burn fuel296+184+31+19+0-2.9

So should you by an electric car with the highest economy?

Not always, no. While the Volkswagen e-Up is clearly very efficient, its claimed range is only just north of 80 miles, which just isn’t good enough for many drivers. At the same time, the Tesla Model S Performance has a range of 367 miles but is one of the least efficient cars in the table above.

It all boils down to that sweet spot of which is just right for you. For many, the best mix of economy, range, price and practicality will likely be cars such as the Nissan Leaf and Hyundai Ioniq Electric.

 

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