How much does an electric car cost to run?

You won't have to buy petrol or diesel, but there's still a fuel cost. Here's how to work out the efficiency of the model you want

Honda e electric car being charged

If you’re one of the increasing number of people considering an electric car, especially in light of the ban on sales of all new petrol- and diesel-engined cars being brought forward by five years to 2030, you have probably wondered how much money you’d save on fuel, in addition to any environmental benefits.

While one of the oft-touted benefits of running a battery-powered car is that electricity costs so much less than petrol or diesel, there is still a cost involved – and if you want to work out exactly what that cost is, you’ll need to know how efficient each electric vehicle (EV) is.

The trouble is, most manufacturers only want to tell you about their cars’ range. And with range anxiety still a concern for many buyers, that makes sense. But what this figure can’t tell you – on its own, at least – is how much your electric car will cost to run. Here’s how to work it out for yourself.

Hang on – what do electric car terms such kW and kWh mean?

You’re not alone. The easiest way to understand all those numbers that seem to fly around whenever electric cars are discussed, or written about, is to think of them in terms of their equivalents in petrol and diesel  – or internal combustion engined (ICE) – cars. 

A kW, or kilowatt, is a unit of power. As its name suggests, it consist of 1,000 watts, and in electrical terms it’s usually used to denote how much power an appliance requires to work; in an electric car, it can also be used to refer to the power output of the electric motor. The ICE equivalent would be brake horsepower (bhp) or metric horsepower (PS).

Bewildered by the terminology? Here, we clearly explain kilowatts and kilowatt hours Credit: Antonio M. Rosario/Getty Images

A kWh, or kilowatt hour, is a unit of energy, and in an electric car it’s usually used to indicate how much energy can be stored in a battery. Put simply, if you were to use an electrical appliance that required 1,000 watts to make it work, you’d use 1kWh of energy in an hour. 

Think of a battery’s kWh rating as being broadly similar to an ICE car’s fuel tank capacity in litres or gallons. So if you had an electric car with a 60kW motor and a 60kWh battery, and if you ran that motor at maximum speed constantly, it would use up the battery in an hour. 

An mpkWh (also written mi/kWh), or mile per kilowatt hour, is a measure of an electric car’s energy efficiency, in the same way as you’d measure an ICE car’s efficiency in miles per gallon. So once you know your electric car’s battery size and its efficiency figure in mpkWh, you can work out how far it should be able to travel on a single charge. 

What else do I need to know?

Finding out how efficient your electric car is, and how much it costs to run, is much like working out how economical any other car is. In an ICE car, you need three things: the size of the fuel tank, how far the car will travel on that amount of fuel, and the cost of the fuel itself. 

It’s much the same with an electric car. You need to know how much electricity you can store – in other words, the capacity of the battery – plus you need to know its range. To work out how much it’s costing you, you’ll also need your mileage and the unit cost of the electricity you’re charging it with. 

Battery capacity

First, you’ll need to know the usable capacity of the battery. However, a word of caution: this probably won’t be the same as the kWh figure provided by the manufacturer, because most manufacturers quote the total capacity of their batteries. 

Most modern electric cars, such as this Jaguar I-Pace, have their batteries in the floor to keep their considerable weight as low as possible

But batteries are not able to be fully discharged without causing permanent damage, so most electric cars use a battery management system to keep a little charge in reserve, which stops the battery degrading too quickly. As a result, the usable capacity will always be slightly less than the total capacity. 

To find out the usable capacity of the battery, you can either ask the manufacturer or dealer, or look it up online on a site such as the ever-valuable EV Database

Range

Make sure you find the official WLTP range figure for your car. This will give you an efficiency figure based on the WLTP (or Worldwide Harmonised Light Vehicle Test Procedure) standard that we use to measure electric car range here in the UK, rather than one based on any other standards from elsewhere in the world. 

Mileage

This is self-explanatory: take an educated guess at the number of miles you travel each week, month or year, depending on the period you want to work out the costs for.

Cost of electricity

Just as fuel costs vary from fuel station to fuel station, so electricity costs vary from provider to provider. Charging companies will have different rates, and the amount it will cost you to charge at home will be different again. 

Cost vary, irrespective of how the electricity has been generated Credit: RONALDO SCHEMIDT/AFP

As with fuel, therefore, one can never predict exactly how much your usage will cost. But you can get a fairly accurate idea. 

If you mostly charge the car at home, that will account for the vast majority of your electricity use. You can usually find the cost you’re paying per kWh on your latest bill. Or if you plan to use a public charger, find out the cost of electricity at the one you’ll be using the most. Charging companies’ rates are usually freely displayed on their websites. 

Great. So what’s next?

To find out how efficient your electric car is, you’ll need to take its range and divide that by the battery’s usable capacity. For example, if you have a car whose WLTP range is 200 miles and your battery’s usable capacity is 40kWh, it should be able to do about 5 miles per kWh, or mpkWh, on average. 

If you also know how much a kWh is costing you, you can then work out how much an electric car will cost to run, by dividing your weekly, monthly or annual mileage by the figure above. This will give you the number of kWh you’ll be using in that time frame, which you can then multiply by your electricity unit cost. 

Charging an electric car at home is likely to be the most cost-effective way of topping up the battery

To continue with the example above, let’s say you’re getting 5mpkWh from your electric car. Let’s also say you’re doing 10,000 miles a year and your electricity costs 15p/kWh. Using these figures, we can work out that you’ll be using 2,000kWh every year to power your electric car – and that that will cost £300 a year, or £25 a month.  

Of course, as with any fuel economy calculation, these figures can never be entirely accurate – they’re based on average electricity consumption figures and costs, after all. But they will provide a fairly accurate idea of how much any electric car will cost you to run.

That should be enough to allow you to compare the costs involved in buying and running different electric cars just as well as you can with petrol or diesel models.

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