What is a hybrid car?

We reveal what a hybrid car is, and how they work

Walk into most car manufacturers' showrooms, and you’ll likely come across at least one or two hybrid models. The industry is quickly moving towards electrification, with hybrid cars the first bridge between conventional petrol and diesel cars and fully electric cars.

They’re popular, too, as hybrid cars and other alternatively fuelled vehicles are the fastest-growing vehicle sector in the UK today. The latest figures show an 18 per cent rise in the number of hybrid vehicles sold in the UK.

In simple terms, a hybrid vehicle is one that 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 relative 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 work?

To understand how a hybrid works, you first need to familiarise yourself with the various different hybrid vehicles.

Parallel hybrid

The most conventional hybrid vehicle is a parallel hybrid, where the car has an internal-combustion engine – likely a petrol unit – as well as a separate battery and an electric motor.

This way, there are three possible ways of powering the car, via the engine alone, via the battery and electric motor, or with the engine working in tandem with the electric motor.

The Toyota Prius is the best example of a parallel hybrid. It was the first hybrid car to be sold in the UK, and has been a sales success ever since its UK launch in 2000.

The current-generation Prius is powered by a 1.8-litre petrol hybrid engine that’s connected to a 53kW electric motor. Depending on the circumstances, the Prius is fully powered by the electric motor, or 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 is 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.

Plug-in hybrid

A plug-in electric hybrid vehicle, otherwise known as a PHEV, 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 on board a PHEV is often bigger than the one found in a parallel hybrid, allowing the vehicle to travel further in pure electric mode. Another important distinction is that as well as being recharged on the move by the vehicle, the electric motor battery has to be plugged in by the owner 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.

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 a parallel hybrid and in a PHEV can drive the car, in a range-extender hybrid the engine is never used for this purpose. Instead, the internal-combustion engine – often a very small petrol unit with a displacement of less than 1.0 litres – is used purely to power the electric batteries when they run out of charge.

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, the battery sizes are often larger than those found in a parallel hybrid or a PHEV.

An example of a range-extender electric vehicle is the BMW i3 Range Extender.

Hybrid car pros and cons – and are they worth it?

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

Furthermore, because city driving often involves a lot of braking, the regenerative brakes will help keep the battery charged, giving you a longer electric driving range.

The same goes for PHEVs and range-extenders. Both will use the electric motor and battery to power the majority of the driving, helping you save on fuel.

Owners of many hybrid cars also won’t have to pay the London Congestion Charge, and face lower tax bills as a result.

Where hybrid cars make less sense is on the motorway and during 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 face a lower tax band than their internal-combustion 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 average CO2 emissions from hybrids.

As an example, a new Toyota Prius will incur a first-year rate of £15, and £130 annually thereafter.

Recent changes to tax bands means all new cars, apart from zero-emissions vehicles, face an annual charge of £140 after the first year. Hybrids, plug-in hybrids and range-extenders are an exception, though, with owners paying only £130 after the first year.

Used hybrids and plug-ins face even lower vehicle taxes. For example, a Prius registered before 1 April 2017 (when the new bands came into effect) pays zero road tax. In fact, any vehicle polluting under 100g/CO2 per km and that is registered before 1 April 2017 pays zero road tax, making all hybrids and plug-ins registered before that date tax free.

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

A parallel hybrid, such as the Toyota 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 via the car’s engine and brakes. However, because of the larger battery sizes on board, a PHEV also needs to be charged externally via a three-pin plug at home, a home charging unit or a public charging unit.

A range-extender is similar to a PHEV in that it also needs to be recharged externally.