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What is a hybrid car?

What is a hybrid car – sometimes called a full hybrid, or hybrid electric vehicle (HEV) – and how do hybrid cars work? Here, we explain everything to do with this side of electrified motoring

These days, almost all car brands sell some type of hybrid-electric vehicle (HEV), with some of them, such as Lexus and Volvo, offering the technology right across their line-ups. Electrification is the biggest trend in the automotive industry right now, so chances are, if you're in the market for a brand-new car, you'll be looking at hybrid options.

Hybrid  sales have been increasing year-on-year during the 2010s and into the 2020s, as buyers look to keep their running costs low and turn away from diesels due to concerns about local air quality. But exactly how do hybrid cars work and what are the differences between the various types of hybrid? Our comprehensive guide is here to explain everything.

In simple terms, a hybrid vehicle is powered by multiple means of propulsion – for example, an electric motor and a petrol engine. But there are several types of hybrid to consider; each has its upsides and downsides. Read on to find out all you need to know about how hybrids work, which types of driving the different kinds are best suited to and whether a hybrid car should be on your shopping list.

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

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

1) Parallel hybrid, or full hybrid: The most common type of hybrid car is known as a 'parallel hybrid' – also called a 'full hybrid'. This is where the car has an internal-combustion engine – likely petrol, but sometimes diesel – as well as a battery and 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 circumstances, the Prius is fully powered by the electric motor, the engine, or a combination of the two.

The battery in the Prius is charged by the engine, meaning there's no need to plug it in to charge. The battery is also charged when braking, thanks to regenerative brakes 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.

2) 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 means of propulsion 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 at home, or use 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.

3) 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 displacement – 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 HEVs worth it?

Where hybrid cars really make sense is in towns and cities. Most parallel hybrids use the electric motor at low speeds – the 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. 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 (HEVs)

Hybrid cars fall into a lower tax band than their internal-combustion-engined equivalents. For example, a Prius (or any other hybrid) costs £145 a year to tax, compared to £155 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 then pays zero.

How do hybrid cars (HEVs) charge – and do you have to charge them?

A parallel hybrid 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 kinetic energy captured 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 can also be plugged in to charge, either at home or at a public charging station.

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