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

By BuyaCar team

There are several variations of hybrid technology commonly found in cars, and each has different battery sizes and makes use of the electrical power in a different way .Plug-in hybrids have larger batteries than other hybrid models and store enough power for around 20-40 miles of electric-powered driving.

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

Hybrid cars are able to regenerate energy when the car slows down - rather than using the brake pads, the electric motor can act as a generator, topping up the battery with otherwise wasted energy as the car slows down. The result is a feeling similar to engine braking when you are in a low gear. Braking alone won’t provide enough power to fully recharge a plug-in hybrid's batteries, though, so you’ll need to plug your car into an electric charging point maximise your hybrid car’s emission-free miles.

Plug-in hybrids are available with either a petrol or diesel powered engine which is combined with an electric motor, providing emission-free electric driving as well as the reassurance of a traditional engine in case you run out of battery. Plug-in hybrids work at their best on short journeys where they can make use of their 20-40 mile electric range and become much less efficient when it comes to longer trips.

Should I buy a plug-in hybrid car?

If buying an electric car seems like too much of a change from what you are used to, but want to move away from petrol or diesel driving, a plug-in hybrid model would be a great option. Regular charging will help you get the most out of a plug-in hybrid car - that way you will spend more time running on electric power and less burning petrol or diesel. This will help you save money on tax and emissions charges and you'll also spend less on fuel.

Plug-in hybrids don’t have huge battery packs compared to electric cars. This means that the maximum you can expect to travel per charge is generally no more than 40 miles, compared with up to 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, and ultimately spend more money. 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 is their high claimed fuel economy figures and low official emissions figures, which can provide company car tax savings.

Emissions regulations are becoming stricter, so manufacturers have been forced to develop this technology, and an increasing number of them are introducing plug-in hybrids to their line-ups. Early examples had ranges of 10-20 miles, but the latest models can offer up to, and sometimes beyond, 40 miles in electric-only motoring, which is enough for most people's average journey.

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.

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

How does a plug-in hybrid work

In many respects, a plug-in hybrid car 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. The Toyota Prius plug-in hybrid has an official fuel consumption of 283mpg - most people probably won’t even get close to this, but may achieve up to 100mpg if they charge regularly and do a lot of town driving, which could be double what drivers find themselves achieving in the self-charging Toyota Prius.

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.

It's also worth remembering that while 100mpg sounds very enticing, helping to cut your costs at the pump, you will be paying for electricity. For a plug-in hybrid family car, it could cost around £3 on a standard electricity rate - or as little as £1 on a cheap overnight rate - to top up enough for around 30 miles' worth of electric motoring.

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.