BMW 330e

What is a plug-in hybrid?

Plug-in hybrid cars are a great option if you want to reduce your environmental impact and fuel costs, but how do they work and should you buy one? Our guide has the answers.

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By Cazoo editorial team

Hybrid cars are becoming increasingly popular as brands and buyers demand a more environmentally friendly alternative to pure petrol and diesel cars. Several types of hybrid cars are available, however. Here, we explain what a plug-in hybrid car (sometimes known as a PHEV) is and why it might be the right choice for you.

What is a plug-in hybrid?

You can think of a plug-in hybrid car as a cross between a conventional hybrid (also known as a self-charging hybrid) and a pure electric car (also known as an EV). 

Like other types of hybrids, a plug-in hybrid has two power sources – an internal combustion engine using petrol or diesel fuel, and a battery-powered electric motor. The engine is the same as that found in regular petrol or diesel cars, while the electric motor is similar to that found in other hybrids and electric cars. A plug-in hybrid’s battery can be recharged by plugging it into a power outlet, which is why it’s called a ‘plug-in’ hybrid.

What’s the difference between plug-in and conventional hybrids?

Conventional hybrids work in much the same way as plug-in hybrids but have built-in systems to recharge their batteries, which is why they’re called  ‘self-charging’. You can’t plug them into a power outlet.

A plug-in hybrid has a bigger battery than conventional hybrid, which is charged by the car itself when it’s on the move but can also be charged by plugging it into a home, public or work charging point. Plug-in hybrids have a more powerful electric motor than most conventional hybrids, allowing them to go much farther using electric power alone. The ability to cover many more miles using only electric power means that the official fuel consumption and emissions figures for plug-in hybrids are far lower than for conventional hybrids, although you need to keep them charged to get the full benefit.

How does a plug-in hybrid work?

Depending on the circumstances, the petrol/diesel engine or electric motor in a plug-in hybrid can power the car by itself, or they can work together. Most choose the power source for you, depending on what’s most efficient and the battery charge level. Pure electric power is generally the car’s default option when you start up and at low speed. 

The latest plug-in hybrids also have several driving modes that alter how the engine and motor work, and you can select these as you wish. For instance, if you’re driving around town and don’t want the car to create pollution, you can select ‘EV’ mode, so your car only uses the electric motor wherever possible.

There also may be a ‘power’ mode in which the engine and motor prioritise maximum power rather than the lowest fuel consumption. This can be useful for overtaking on a country road, or when towing a heavy trailer.

How are a plug-in hybrid’s batteries recharged?

The primary way to recharge a plug-in hybrid’s batteries is by plugging it into a home or public charging point. How long it takes to recharge depends on the size of the car’s battery and what sort of charger you’re using. As a rule of thumb, though, a completely flat battery should fully recharge overnight.

Plug-in hybrids also have several built-in systems that recharge the batteries as you’re driving. The main one is by regenerative braking. This reverses the direction in which the electric motor spins when you brake, turning the motor into a generator. The power that is generated then goes back into the batteries. In many plug-in hybrids, this also happens when you ease off the throttle.

Plug-in hybrids can also use their engine as a generator to recharge the batteries. This happens without any input from the driver, as the car’s computers constantly use these systems to keep as much charge in the battery as possible. If the batteries run flat while driving, the car simply continues on petrol/diesel engine power.

What happens if you don’t plug in a plug-in hybrid?

The worst that’ll happen is that the battery will run flat, so you won’t be able to use the electric motor until you recharge it. The car will still be perfectly drive-able because it can use its petrol/diesel engine instead.

The car’s built-in power generation systems generally prevent the electric motor’s battery from running flat, but there are some situations where it might happen – on a long motorway drive, for instance.

How far can a plug-in hybrid go on electric-only power?

Most plug-in hybrids give you an electric-only range of between 20-40 miles when fully charged, although some can do 50 miles or more. That’s enough for many people’s daily needs, so if you're able to keep the battery topped up you might be able to make many journeys using zero-emissions electric power.

How far a plug-in hybrid can go before its fully charged battery runs flat depends on the size of the battery and how you’re driving. Travelling at higher speeds and using lots of electrical features such as the headlights and air con will drain your battery more quickly.

What fuel economy will a plug-in hybrid do?

According to official figures, many plug-in hybrids are capable of going hundreds of miles on a gallon of fuel. But in the same way that most petrol or diesel cars don’t match their official mpg figures in the real world, neither do most plug-in hybrids. The discrepancy isn’t dishonesty by the car’s manufacturer – it’s simply a quirk of how the average figures are obtained in laboratory testing. You can read more about how the official MPG figures are calculated here

Even so, most plug-in hybrids give extremely good fuel economy. The BMW X5 PHEV, for instance, can give you better fuel economy than a diesel X5 would give. To get the best fuel economy from plug-in hybrids, you need to plug in to recharge as often as possible.

What’s a plug-in hybrid like to drive?

When the engine’s running, a plug-in hybrid feels the same to drive as any other petrol or diesel car. When it’s running on pure electric power, it feels like an electric car – which can be a little eerie if you’ve not experienced one before because there’s so little noise and most accelerate very quickly and smoothly from a standstill.

The way a plug-in hybrid’s petrol or diesel engine starts up and shuts down while driving, often seemingly at random, can seem a bit strange at first, too. 

The brakes also take a bit of getting used to, and it’s worth noting that some plug-in hybrids are very fast. Indeed, the fastest version of some cars are now plug-in hybrids – the Volvo S60, for example.

Are there any downsides to plug-in hybrids?

Plug-in hybrids can give great fuel economy but, as we’ve already mentioned, you’re very unlikely to achieve the official maximum. A factor in the discrepancy between the official and real-world fuel economy is that plug-in hybrids can use more fuel than you might expect when running on the engine alone. The batteries, electric motors and other components in the hybrid system are heavy, so the engine has to work harder, and use more fuel, to move it all.

Plug-in hybrid cars also cost quite a bit more to buy than the same car with a petrol/diesel engine. And, as with an electric car, if you live in a flat or house without off-road parking you might not be able to install a home charging point.

What are the upsides to plug-in hybrids?

According to official figures, most PHEVs emit very little carbon dioxide (CO2) from their exhaust. Cars are taxed on CO2 emissions in the UK, so road tax for PHEVs is usually very low.

Drivers of company cars in particular could save thousands of pounds a year on road tax by getting a plug-in hybrid. The cars also are exempt from most charges for driving in low emissions/clean air zones. These two factors alone could be enough to persuade many people to buy a plug-in hybrid.

And, because plug-in hybrids have both engine and battery power, the ‘range anxiety’ that can surface with driving an electric car isn’t an issue. If the battery runs flat, the engine takes over and your journey continues.

You’ll find a range of high-quality plug-in hybrids available at Cazoo. Use our search tool to find the one that’s right for you, then buy it online and have it delivered to your door, or choose to collect it from one of our Customer Service Centres.

We’re constantly updating and adding to our stock. If you can’t find one within your budget today, check back soon to see what’s available or set up a stock alert to be the first to know when we have a plug-in hybrid that matches your needs.