What is a hybrid car?

Here's what a hybrid car is, and how they work

Bentley Bentayga Hybrid

Nearly every car manufacturer is offering some type of hybrid model in its range these days, with some, such as Lexus and Volvo, offering it across their line-up. Electrification is the biggest trend in the automotive industry right now, so the chances are, if you're buying a new car, you'll be faced with at least some hybrid options.

Hybrid sales have been rising by the year, as consumers look to minimise their running costs and turn away from diesels due to concerns about local air pollution. But how do hybrid work, and what's the difference between the various types? Our simple guide is here to explain it all.

In simple terms, a hybrid vehicle is powered by multiple sources – for example, an electric motor working with a petrol engine. There are several types of hybrids to consider, and each has its pros and cons. Read on to find out all you need about how hybrids work, which situations they suit the most, and whether a hybrid should be on your shopping list.

How does a hybrid car work and what are the different types?

There are several different types of hybrid cars, and although all combine electrical and fossil-fuel power to some degree, each works in a slightly different way. Here's a rundown of them all.

Parallel hybrid

The most conventional type of hybrid vehicle is called a 'parallel hybrid', where the car has an internal-combustion engine – likely a petrol, but sometimes diesel – as well as a battery and an electric motor. There are three possible ways of powering the car: using the engine alone, using the electric motor alone, or with the engine working in tandem with the electric motor.

The Toyota Prius is perhaps the most well-known parallel hybrid. It was the first hybrid car to be sold in the UK, and has been a sales success ever since its launch in 2000. The current Prius is powered by a 1.8-litre petrol engine paired with an electric motor. Depending on the circumstances, the Prius is fully powered by the electric motor, the engine, or a combination of the two.

The nickel-metal-hydride battery in the Prius is charged by the internal-combustion engine, meaning there's no need to plug it into a charging station. The battery is also charged when braking, thanks to the regenerative brakes on board that store kinetic energy and transfer it to the battery. The downside of this type of hybrid is that it can only travel in zero-emissions electric mode at low speeds and for very short distances.

Plug-in hybrid

A plug-in hybrid electric hybrid vehicle, or PHEV for short, is similar to a parallel hybrid in that there are two engines on board: an internal-combustion engine and an electric motor. Again, they can work either alone or in tandem.

However, the key difference is that the battery of a PHEV is bigger than a parallel hybrid's, allowing the car to travel further in pure electric mode. Another important distinction is that as well as being recharged on the move, the electric motor's battery can be plugged in to recharge.

This means owners must either have a way to recharge their car at home, or use one of the thousands of public charging points, in order to make the most of the PHEV's electric range and thus keep their running costs to a minimum. A common example of a plug-in hybrid electric vehicle is the Mitsubishi Outlander PHEV.

Range-extender hybrid

A key difference here is that while the internal-combustion engine in parallel hybrids and PHEVs can drive the car's wheels, in a range-extender, the engine is never used for this purpose. Instead, the internal-combustion engine – often a very small petrol unit less than a litre in size – is used purely to recharge the batteries when they run out.

The car is fully driven by the electric motor, or motors, on board. Because the range-extender hybrid relies on the battery to power the vehicle, battery sizes are often larger than those in a parallel hybrid or a PHEV. As the range of pure-electric cars has increased, range-extenders have fallen out of favour; BMW no longer produces the 'REx' version of the i3, for example.

Hybrid car pros and cons – are they worth it?

Where hybrid cars really make sense is in town and city centres. Most parallel hybrids use the electric motor at low speeds – the Toyota Prius, for example, uses its electric motor to power the car only below 15mph.

Furthermore, because city driving often involves a lot of braking, the regenerative brakes help keep the battery charged, giving you a longer electric driving range. The same goes for PHEVs and range-extenders. Both use the electric motor and battery to power the majority of driving at low speeds, helping you save fuel. Most plug-in hybrid cars are exempt from the London Congestion Charge, too.

Where hybrid cars make less sense is on the motorway and for long drives. This is because the battery power is quickly drained, with the car having to rely on the internal-combustion engine to keep moving.

Road tax for hybrid cars

Hybrid cars fall into a lower tax band than their internal-combustion-engined equivalents. This is because vehicle tax in the UK is based on carbon-dioxide emissions per kilometre, and the electric motors on board – which are zero-emissions – lower the overall CO2 emissions from hybrids.

For example, a Prius (or any other hybrid) costs £135 a year to tax, compared to £145 for a purely petrol or diesel vehicle. Used hybrids and plug-ins have even lower tax rates. For example, a Prius registered before 1 April 2017 pays zero road tax. In fact, any vehicle emitting under 100g/km of CO2 registered before 1 April 2017 pays zero road tax.

How do hybrid cars charge – and do you have to charge them at all?

A parallel hybrid, such as the Prius, doesn’t need to be plugged in to charge. Instead, the on-board battery is charged by the internal-combustion engine as the vehicle drives, and also via the kinetic energy created when braking.

With a plug-in hybrid electric vehicle, charging is also done using the engine and brakes. However, because of their larger battery sizes, PHEVs also need to be plugged in to charge, either at home or at a public charging station.