What is a plug-in hybrid car?

Hybrids blend petrol or diesel and electric power for lower emissions while plug-in hybrids have larger batteries and greater electric range

BuyaCar team
Aug 25, 2020

Not to be confused with other types of hybrid cars - which have small batteries and electric motors that offer a mild boost - plug-in hybrids have large battery packs that store enough charge to power the car by themselves for up to around 30 miles.

Due to their larger size, however, the batteries in plug-in hybrid models need to be charged in the same way electric cars do - hence the 'plug-in' part. If you don't do this, the battery runs out of charge, with the car resorting to using its petrol or diesel engine, which dramatically increases fuel consumption and emissions.

Yes, plug-in hybrids may add some charge back to the battery when braking, but this only offers a small boost and is an inefficient way to use a plug-in hybrid. Meanwhile, conventional hybrids use braking to recharge their far smaller batteries and can't be plugged into the mains as plug-in hybrid and electric cars can.

With a battery and motor like electric cars, plus a petrol or diesel engine, plug-in hybrids on paper offer the best of both worlds. Fully charged, they are able to cover 20-30 miles on electric power before the engine takes over. This means fuel economy is exceptional on short journeys, but much worse on longer trips. 

Plug-in hybrid cars: the good

✔ Electric range of more than 20 miles
✔ Low fuel bills if you charge regularly
Minimal company car tax

Plug-in hybrid cars: the not-so-good

Need frequent charging for good fuel economy
Long run fuel economy can be worse than diesel
Electric cars make more sense for many drivers

Should I get a plug-in-hybrid car?

Volvo V90 side

If you're not quite sold on the idea of an electric car, but don't want a conventional petrol or diesel model, a plug-in hybrid model could be a good halfway house. Use a plug-in hybrid as it's intended - charging regularly, so that you spend more time running on electric power and less burning petrol or diesel - and not only can you save money on tax and emissions charges, you'll also spend less on fuel.

Unlike electric cars, plug-in hybrids don't have huge battery packs. This means that the maximum you can expect to travel per charge is around 30 miles, compared with 150 miles or potentially 250 miles with many electric models. However, once the battery runs out plug-in hybrids have a petrol or diesel engine that then kicks in, potentially transporting you another few hundred miles before you have to fill up the tank and recharge the batteries.

The key thing to remember with plug-in hybrids, though, is that they work best if you predominantly cover short journeys and recharge after each one. This will mean that you burn less fuel and rely more on cleaner electric power.

Fail to charge often and the car has to lug all the weight of the batteries and electric motor around with little benefit, meaning you'll burn more fuel and produce more emissions. However, if you only cover short journeys, many electric cars offer more than enough electric range for you to complete all your journeys on 100% electric power.

Meanwhile, if you regularly cover longer journeys that are too lengthy for an electric car to complete on one charge - which for the current crop of electric cars typically means well over 200 miles - then you'll get little benefit from the electric motor with a plug-in hybrid. Especially if most of your driving is on the motorway. If that applies to you an economical petrol or diesel model could provide similar real-world fuel economy.

With all this in mind, it's worth considering whether the type of driving you do suits a plug-in hybrid. Another plus point for plug-in hybrids are high claimed fuel economy figures and low official emissions figures, which provide company car tax savings.

Emissions regulations are becoming stricter and stricter, so manufacturers have been force to develop this technology, and more and more of them are introducing plug-in hybrids to their line-ups. Most of the current breed offer an official electric range of around 30 miles on electric power alone, which will be more than enough for most people to take a trip to the shops.

Being able to take the strain off the conventional engine with electric power also helps to boost fuel economy figures, which can be as high as 200mpg or more. Just remember that you'll only achieve figures like this if you mainly do short journeys and regularly recharge the car.

How plug-in hybrid cars work

In many respects, a plug-in hybrid works in a similar way to a regular hybrid, albeit with a much bigger battery pack and the ability to manually plug the batteries in. To power the car plug-in hybrids have either a petrol or diesel engine, plus an electric motor. The electric motor is powered by a battery pack.

Regular hybrids charge their batteries on the move using the petrol engine and 'regenerative braking', which is where the car recycles energy otherwise lost when slowing down.

Plug-in hybrids, meanwhile, have larger, higher capacity batteries. This is good for electric range, but they do need to be charged independently. In other words, they need to be plugged in.

If you don't do this, the car relies on the petrol or diesel engine and is likely to burn through lots of fuel, as they have to carry all the weight of the electric motor and batteries but without any electric assistance.

Do plug-in hybrid cars improve fuel economy?

Yes and no. If you regularly charge a plug-in hybrid, and only use the engine as a last resort, you’ll see very good fuel economy figures. Toyota’s Prius plug-in hybrid has an official fuel consumption of 283mpg. Most people probably won’t even get close to this, but, may achieve 95-100mpg if they charge regularly and do a lot of town driving.

If you don’t regularly charge the battery, expect mpg to be much, much worse. This is because you’re lugging around potentially another 100kg worth of batteries - or even more - which will act as a dead weight. Imagine carrying around a couple of passengers at all times. That's effectively what you're doing if you don't charge the batteries.

Incidentally, electric models are most economical around town than on the motorway. The Toyota Prius plug-in will cover around 30 miles around town on electric power, but only 20 miles at motorway speeds. This means that if you spend much of your time on the motorway a plug-in hybrid is not likely to be the wisest choice.

Since many electric cars can already cover 150 miles to 250 miles per charge on electricity alone, one of these would be a more sensible choice, provided you don't do hundreds of miles on the motorway in one go. Alternatively, an economical diesel is likely to be more economical on long motorway trips than a plug-in hybrid and you don't have to worry about recharging, as you would with a plug-in hybrid or electric car.

 

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