How does a plug-in hybrid work? The difference between electric cars explained, and how much they cost to run


In a few years the car market in Britain has changed short. Forget the traditional choice between petrol and diesel models – now there is a seemingly dizzying array of technologies on offer, from hydrogen to hybrid and fully electric cars.

Electric motoring is at the front of the pack.

Propelled by high petrol and diesel prices and city-centre charges for polluting vehicles, drivers are jumping over to zero-emission motoring in their droves.

Pure electric models are proving most popular: there are now half a million pure electric cars on UK roads, with sales increasing by 14 per cent every month.

Meanwhile, tens of thousands of plug-in hybrids are also sold to British drivers every month, as those wary of relying on public charge points seeking a halfway house between fossil fuels and electric motoring.

Yet critics of plug-in hybrids warn they can be inefficient and polluting if not used properly, and many motoring experts say drivers should steer clear of hybrids and jump straight to battery electric cars.

So what is the difference between a plug-in hybrid and a pure EV, and which is better?

What is the difference between an EV, a hybrid, and a plug-in hybrid?

A “pure” electric vehicle runs exclusively on battery power. That means it has no combustion engine under the bonnet, and it produces no exhaust fumes.

By comparison, a “mild” hybrid relies on an electric motor and tiny battery for starting and driving at low speeds. There’s no need to plug the car in to recharge – it harvests the energy from braking to store in the battery for later use. But as mild hybrids mainly use petrol for normal driving, they do not cut driving emissions significantly.

A plug-in hybrid contains a bigger battery alongside a combustion engine. The battery – which like a fully electric car needs to be plugged in and charged – allows the car to be driven in zero-emission mode for up to 50 miles.

What are the benefits of a hybrid car?

Fully electric cars need to be plugged in and powered up before they can be used. For drivers with a private driveway and plug point, this is not usually a problem. But public charge points can be scarce and unreliable, making driving trickier for people without a private plug.

Hybrid cars essentially feature a back-up combustion engine, so drivers do not have to stop and plug in if they run out of battery range. They are promoted as the ideal solution for people who want a car for zero-emission driving around towns and cities that is also well suited for longer road trips.

Are hybrid cars good for the planet?

Repeated studies have proved that electric cars are better for the environment than petrol or diesel vehicles, even when they are charged from fossil-based electricity sources.

However the verdict is less clear when it comes to plug-in hybrid electric vehicles.

Carmakers promote their plug-in hybrids as a green choice for drivers not ready to embrace a pure electric model.

But research from pressure groups Transport & Environment and Greenpeace suggest plug-in hybrids often don’t live up to carbon saving claims made by carmakers.

Official tests suggest plug-in hybrids emit an average of 44g of CO2 equivalent per kilometre, but tests under “real world” driving conditions see them emit 120g per km, the groups claim.

This would mean a plug-in hybrid would only reduce emissions by about a third, compared to a conventional petrol car.

Other studies suggest that in worst-case scenarios, emissions from a plug-in hybrid can be higher than even a conventional petrol or diesel car.

Plug-in hybrids need to be plugged in

Part of the problem with plug-in hybrids is that many owners rarely remember to plug their cars in to charge the battery. Instead, they rely on the combustion engine, which has to work harder and use more fuel to cart around the extra weight of the unused battery. This produces higher emissions.

How much does a hybrid car cost to run?

How much hybrid cars cost to run largely depends on how they are used. If drivers make good use of the battery then running costs are lower than a traditional petrol or diesel car. But if the battery is rarely used, those costs can jump significantly.

Consumer experts say pure electric cars are the cheapest to run. Driving an electric BMW 318i for example costs around 3.7p per mile, according to the website GreenCar, compared to 14.2p per mile for the petrol version of the car.

Which type of car is more popular?

There are signs the warnings around plug-in hybrids are filtering through to sales data.

Sales of battery electric cars are growing fast, with new registrations jumping 15 per cent last month, according to the Society of Motor Manufacturers and Traders. In fact, battery electric cars were the only vehicle type to register sales growth in June.

By comparison, “mild hybrid” cars and plug-in hybrids both registered double-digit sales slumps.

What does the Government think?

Last summer the Government confirmed that sales of hybrids – including plug-in hybrids – will be banned from 2035. All new cars and vans be fully zero-emission at the tailpipe from this date, it said.

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