What is a hybrid car?

October 06, 2020 by

Hybrid cars are becoming ever-more popular as legislation and public opinion swings away from petrol and diesel-powered cars. But what exactly is a hybrid car and should you buy one? carwow explains.

  • Hybrid cars: a history
  • How does a hybrid car work?
  • What are the advantages and disadvantages of a hybrid car?
  • Are there different types of hybrid car?
    • What is a mild hybrid?
    • What is a self-charging a hybrid?
    • What is a plug-in hybrid?
    • What is a range-extender hybrid?
  • How far can I drive a hybrid car?
  • How far can I drive a hybrid car on battery power?
  • What happens if my hybrid car runs out of battery power?
  • How long do a hybrid car’s batteries last?

Hybrid cars combine a conventional internal combustion engine (ICE) with a battery-powered electric motor. At low speeds, the car is powered by electricity alone. As speed increases, the engine takes over. Under certain conditions, the engine and electric motor work together to provide more power or recharge the batteries.

The first hybrid car appeared in 1900, designed by a certain Ferdinand Porsche, who later achieved some success with cars bearing his name. The technology was developed throughout the 20th Century, but it wasn’t until the 1990s that Toyota perfected it, launching the first Prius in 1997.

Sales outside Japan started in 2000; it was little more than a curiosity until the second-generation version was launched in 2004, becoming a massive sales hit around the world. More than six million and counting have now been sold.

Other manufacturers followed Toyota’s lead, launching their own hybrids. They chose their timing well. In the early 2000s, concerns were growing about increasing carbon dioxide emissions causing climate change. Thus, legislators started giving tax breaks to cars with low CO2 emissions, which particularly favoured hybrids. Since the UK launched its CO2-based road tax regime in 2004, most hybrids have been tax-free. That alone prompted many people to switch to hybrids, especially company car drivers and fleets who can save thousands of pounds a year on their tax bill.

Anyway, enough scene-setting. Let’s dig into how a hybrid-powered car actually works.

How does a hybrid car work?

Hybrid-powered cars use two energy sources: fuel powering a conventional diesel or petrol engine, and a battery powering an electric motor. Exactly which energy source the car uses at any given moment depends on the situation.
When trickling along in stop-start traffic, the car may run on battery power alone. This not only saves fuel, it also means the car isn’t producing any tailpipe emissions – particularly desirable when stuck in city centre congestion. As an added bonus, the car will be pretty much silent, as well.

The electric element of a hybrid car’s powertrain is optimised for low speed running, thus the petrol or diesel engine takes over as speed increases. At that point, the car behaves like any other conventional car.

The petrol or diesel engine and electric motor can work together to provide extra power. The engine can also work as a generator to recharge the battery. Regenerative braking recovers energy that would otherwise be lost while slowing down and feeds it back to the batteries. Some hybrid cars have other energy recovery systems and, of course, some can be plugged into a socket to recharge, as well.

Driving a hybrid car, you need to do nothing more than, err, drive it. The car’s immensely clever technology works out exactly which energy source or combination thereof is best at any given moment. However, most of the latest hybrids do give you the option of specifying which power source is used at the press of a button.


What are the advantages and disadvantages of a hybrid car?

Hybrid cars offer flexibility that electric cars (EVs) and conventional petrol and diesel cars don’t. They can run on battery power alone, producing no tailpipe emissions or noise, benefitting the environment and your stress levels. They also emit very little CO2 and, since the cost of road tax in the UK is based on CO2 emissions, could save you an awful lot of money.

A hybrid car also retains the biggest benefit of a normal petrol or diesel car: when it runs out of fuel, you simply refill the tank and carry on your way. There’s no range anxiety and you don’t have to faff around with the UK’s haphazard charging infrastructure. Some, like the Porsche Panamera Turbo S e-Hybrid, are ludicrously fast, as well.

On the debit side, hybrids rarely achieve their claimed fuel economy. Even five years ago, most would achieve real-world economy that was uncompetitive against many diesel-powered cars. That’s still largely true but some, like the latest Toyota Corolla, are at least on par. Really, it’s still the case that hybrids make most sense if you can maximise the amount the battery-only running, for instance on a short commute or mostly driving in urban areas.

Are there different types of hybrid car?

There are indeed several different types of hybrid-powered car: mild hybrid, self-charging hybrid, plug-in hybrid and range-extender hybrid. Read on below to find out more about how each type works.

What is a mild hybrid?

Mild hybrids use a small-capacity battery charged via regenerative braking and other energy recovery systems. They are capable of running on battery power alone at speeds up to about 12mph, and when coasting (i.e. when the driver lifts off the throttle) at up to motorway speeds. They won’t go very far on battery power alone, though – a couple of miles at most.

This type of hybrid powertrain is becoming increasingly common, found in everything from the latest Audi RS6 to the Ford Puma. This is because they improve a car’s fuel economy and CO2 emissions on the current WLTP testing cycle. The jury seems to be out on their effectiveness in improving fuel economy in real-world driving, though.

Still, expect to see them on every car that isn’t a true hybrid or electric in the not too distant future as they help bring down the average CO2 emissions of the range of vehicles a car manufacturer makes. This helps car makers avoid paying tough fines for not reaching emissions targets

What is a self-charging a hybrid?

Self-charging hybrids generate all the power their batteries need from systems on the car – the engine, regenerative braking, exhaust heat recovery, and so on. They can drive further and faster on battery power alone than mild hybrids – perhaps 10 or 12 miles at speeds up to 40mph or so.

Toyota and its luxury car division, Lexus, are currently the leading exponents of the self-charging hybrid. Honda, Hyundai, Kia and Mercedes each offer several, as well.

What is a plug-in hybrid?

A plug-in hybrid can be recharged by plugging it into an electrical outlet, as you would with an electric vehicle. They also use regenerative braking and other energy recovery systems to feed power back into the batteries when the car is in motion.

Many plug-in hybrids are capable of going further and faster on battery power alone than self-charging hybrids – as much as 50 miles at up to motorway speeds. Most allow you to lock the car into battery-only running at the press of a button.

Some manufacturers – BMW and Porsche, for instance – pair their plug-in hybrid systems with powerful petrol engines. When the electric motors and petrol engine work together, performance can be pretty spectacular. But, when running using just the engine alone, fuel economy will be no better than an equivalent non-hybrid car. Probably worse, actually, as all the hybrid system gubbins add a lot of extra weight, so the engine has to work harder.

Also worth bearing in mind that you might not see the 100-plus mpg the manufacturers claim of their plug-in hybrids. Those numbers are the result of very complex calculations based on a mix of battery, engine and battery/engine running on the WLTP test cycle. But, if you can maximise the amount of battery-only driving you do, you will ultimately use very little fuel.

What is a range-extender hybrid?

A range-extender hybrid uses both an electric motor and a conventional engine like every other type of hybrid. However, uniquely, the engine isn’t connected to the driven wheels. Rather, it serves as an on-board generator to recharge the batteries on the move. Perhaps the best-known range-extender at the moment is the LEVC London taxi.

As it’s only being used as a generator, the engine doesn’t use much fuel, but still allows the car to go much further than it would on battery power alone. The aforementioned taxi has a battery-only range of 63 miles, but the engine gives it a total range of up to 301 miles, draining the 30-litre fuel tank. By comparison, a conventional petrol-powered car returning 35mpg would use 43 litres of fuel to cover that distance.

How far can I drive a hybrid car?

You can drive a hybrid car as far as you want. Like a conventional car, you simply refill the fuel tank when needed and carry on your way. So, they are no more hassle in that regard than a petrol or diesel car.

How far can I drive a hybrid car on battery power?

How far and how fast you can go on battery power alone in a hybrid car depends on what sort of hybrid it is. Mild hybrids might only manage a couple of miles at up to 12mph or so. Self-charging hybrids will achieve something in the order of 10 to 15 miles at up to 30 or 40mph. Plug-in hybrids might go as far as 50 miles at anything up to 100mph.

But these are only ballpark numbers. Range and speed varies widely across different car manufacturers and how you drive the car.

What happens if my hybrid car runs out of battery power?

Theoretically, this shouldn’t happen. The car’s immensely clever technology manages the energy recovery systems and engine usage to keep the batteries at least partly charged at all times. If that isn’t happening, the car probably needs servicing. But you’ve still got the normal combustion engine, so the car won’t actually stop working.

How long do a hybrid car’s batteries last?

The batteries in very early hybrid cars like the first-generation Toyota Prius and Honda Insight needed replacing after 150,000 miles or so. But that was 20 years ago, and the technology has improved to the extent that most hybrids will rack up two or three times that mileage without issue. We’re aware of a third-generation Prius taxi that’s still going strong having racked up well over half a million miles on its original batteries.

You’ll be able tell when the battery is coming to the end of its life if it drains quickly and recharges slowly – just like your phone. Expect a hefty bill if they do need replacing.


Is a hybrid car worth it?

If you’re a company car buyer, hybrids are pretty much a no-brainer. Their low CO2 ratings can translate to massive savings on benefit-in-kind tax rates. For private buyers, though, the picture is less clear cut.

We’ll take mild hybrids out of the equation here, as they have little useful battery-only capability. If the car you want is a mild hybrid, fair enough. But if you are shopping for, say, a small crossover, there are more pertinent things to judge them on than whether they are a mild hybrid.

Self-charging and plug-in hybrids are at their best in low to medium speed urban driving with lots of braking. It maximises the amount of battery-only running that’s possible and keeps the batteries topped up.

The case falls apart on motorways, though. High-speed running drains the batteries and too little braking is done to recharge them. At that point, a hybrid becomes a conventional petrol or diesel car that will return fuel economy no better than a non-hybrid.

So, it entirely depends on what sort of driving you do. If most of your driving is in urban areas, you will get the most out of a hybrid’s battery-only running capability. Indeed, the ICE may only come into play on those occasional longer journeys. The fuel savings could really add up – that’s why taxi drivers love them. If you mostly do long-distance motorway slogs, though, you may want to look elsewhere.