What is a plug-in hybrid car? What does PHEV mean? | Top Gear
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Thursday 5th October

What is a plug-in hybrid car? What does PHEV mean?

What is a plug-in hybrid, you ask? It’s two cars in one, in a nutshell. Allow us to explain…

Published: 12 Apr 2023

If you’ve not bought a car in a while, you’ll be amazed at how things have advanced in recent years. The arrival of hybrid and electric cars are major steps towards eco-friendly driving, but they have also made car buying vastly more complicated.

You’ll have realised this if you’ve just been bombarded with phrases like ‘plug in hybrid’, ‘mild hybrid’, ‘PHEV’, ‘kilowatt-hours’ and all the other jargon that has infiltrated the car world over the last decade.

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Plug-in hybrids are especially difficult to decipher, because they combine the petrol powertrain you’re accustomed to with electric abilities that need explaining from scratch. That’s why you’re here, right?

Don’t fret, we’ll have you up to speed in no time. So, fire away with your burning PHEV questions.

Right, what does PHEV mean?

Easy. PHEV stands for Plug-in Hybrid Electric Vehicle. The acronym (pronounced ‘fev’, and absolutely not ‘pee-hev’) is used frequently because plug-in hybrid electric vehicles takes a long time to say. And type.

And what is a plug-in hybrid electric vehicle?

A plug-in hybrid is a type of car that can run using a combustion engine like a normal car, or using an electric motor and battery like an electric car. Yep, it’s two cars in one.

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It’s called a plug-in hybrid because you have to plug in a cable to charge the battery: this is what gives you a certain amount of zero-emissions range, for which you can drive around without using the engine and with nothing coming out of the tailpipe. Polar bears, rejoice!

Once the battery runs out, the engine seamlessly kicks in and you’re back to driving a normal car again. So for short distances you’ve got all the benefits of driving an electric car without the drawback of having to worry about charging when you travel further afield.

And this is different from other types of hybrid, yes?

It’s a bit like how all thumbs are fingers but not all fingers are thumbs: you can call a PHEV a hybrid but not all hybrids are PHEVs.

A plug-in hybrid is the most sophisticated type of hybrid car there is. Other hybrids (you might have heard of ‘mild hybrids’ or ‘self-charging’ hybrids) are simpler because they use much smaller batteries, which means they can usually travel no more than a mile or two without the engine.

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These can’t be plugged in as the car charges the battery itself with power from the engine or braking, and while that’s more efficient than a non-hybrid combustion car, all the energy still ultimately comes from the fuel tank.

So how does a plug-in hybrid work?

Easy, you fill up with petrol or diesel (most PHEVs are petrols, don’t ask us why) as normal, but when you get home you plug the car into the mains using a special socket and cable. Most people will get an external home charging unit (often called a wallbox) fitted to their house or garage to allow this, though some get by with an extension lead. Best avoided if you can.

Once full, the battery will give you a certain amount of electric range so that the car can travel without needing the engine at all. Depending on the model you’ll typically get between 20 and 60 miles from a full battery, but expect about a third less than the manufacturer claims on paper. You can read about the longest-range PHEVs by clicking these blue words.

Most PHEVs have an electric mode, a hybrid mode and a combustion mode. E-mode compels the car to use only the electricity in the battery (until there’s none left); hybrid mode will work out the most efficient way to deploy the battery and engine power along your journey, alternating between the two; combustion mode will let you hang on to your charge until you need it. This could be very handy if you’re driving into an urban area and you don’t want the local city folk to inhale your exhaust fumes. You considerate thing.

In electric mode, a PHEV will send the electricity in its battery to the motor(s) to provide drive. Some are capable of driving up to motorway speeds unaided, although others will need the engine to step in and help beyond a certain speed.

In hybrid mode, a computer will work out when’s best to use the engine and motor, often flicking between the two (or using both at the same time) while you drive. You don’t need to do anything other than drive normally here, and the best PHEVs will blend the two power sources so seamlessly that you’ll barely notice the change behind the wheel.

If plugging in and charging isn’t convenient (or you simply can’t be bothered with all that faffing around) then a PHEV might not be for you. Some models allow you to charge the battery on the go using the engine as a makeshift generator, but this is horribly inefficient and kinda defeats the object.

This isn’t the same as regenerative braking (or regen braking for short), where the car recycles electricity back into the battery as you slow down. Thus giving you a small amount of free (ish) range. Clever, eh?

I’m with you now. How long does charging take?

Again, depends on the model. PHEVs have much smaller batteries than you’ll find in fully electric cars (typically measuring around 10 to 20kWh in size, though some blow this range out the water) but they also do without the rapid charging tech that allows EVs to be topped up in under an hour. Because, when you’ve got a tank of petrol to fall back on, that’d be overkill.

On a normal domestic supply of 2-3kW you’re looking at a charge time of five hours or more, which sounds rubbish but is perfectly adequate if you’re plugged in overnight at home or at the office during the day. One of those wallboxes mentioned above could bump you up to 7kW or more, thereby slashing your top-up times.

And this is why PHEVs manage enormous fuel economy figures, yes?

Capable, they are capable of enormous fuel economy figures. This is very different to actually achieving what the manufacturer claims is possible based on the lab test.

PHEVs mostly claim fuel economy in the triple-digit-mpgs because in the official test procedure they are driven a set distance starting with a full battery. The bigger the battery, the more of a head-start they effectively get over normal petrol and diesel cars. Doesn’t seem fair, does it?

So, if you charge your plug-in hybrid religiously you might drive for weeks on end without needing the battery at all. Woo hoo, infinite mpg! Or you could drive hundreds of miles on the motorway and find your fuel economy is hardly any better than it was with your old combustion-engined model. Chances are you’ll fall somewhere in between those two extremes. The more you plug in, the less you’ll visit the pumps.

What else should I know about plug-in hybrids?

They tend to be more expensive than petrol and diesel equivalents because more tech equals more money. And although the batteries are smaller than those found in electric cars, even a few kilowatt-hours’ worth of cells is a hefty weight to lug around, so they’ll be heavier than non-hybrid versions as well as pricier.

The presence of a battery also has implications for interior space: most PHEVs will have theirs stowed somewhere under the back seats and boot, which typically means less room for bags and, y’know, stuff.

However, PHEVs have a habit of being the most powerful versions in model line-ups, as the combined power of engine and motor means hot-hatch embarrassing acceleration.

Take the Volvo XC90 T8 plug-in hybrid, as a random example: it’s a whopping great family SUV packing 385bhp and it’ll do 0-62mph in 5.4 seconds, for goodness’ sake! Ever needed your school run wagon to outpace a Ford Focus ST? Of course not, but here we are.

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