What is a plug-in hybrid car?
What is a plug-in hybrid, how can it cut pollution and running costs, and should you buy one?
The UK Government recently delayed the 2030 UK petrol and diesel sales ban to 2035 – it's worth noting that this was always the cut off date for the sale of hybrids (HEVs)and plug-in hybrids (PHEVs) that can travel a 'significant distance' on electricity alone. Many manufacturers have pledged to go fully electric or hybridise their entire lineups before that date, and with ever more PHEVs on the market, it's more important than ever to clue yourself up on what a plug-in hybrid car is.
Unlike a standard hybrid car, which is only capable of pure-electric running over short distances, a plug-in hybrid can be driven for a far greater distance on electric power only, typically between 25–50 miles. Though some examples, such as the Polestar 1, can travel for distances in excess of 90 miles in all-electric drive.
Plug-in hybrids represent a vital stepping stone between the petrol or diesel cars that the vast majority of people drive today, and a zero-emissions future. For most owners, the fact that plug-in hybrid models can save them money will also help them find favour, with the fact they're also designed to reduce pollution being a happy bonus.
Read this guide and you’ll understand not only how a plug-in hybrid car works, but also how choosing to drive one could reduce your motoring bills.
How does a plug-in hybrid work?
You may be aware of popular hybrid models such as the Toyota Corolla and Yaris, which all combine a petrol engine, a small battery and a small electric motor that assists the engine. This allows for pure-electric running at low speed over very short distances without using any fuel. Plug-in hybrids allow a greater distance to be driven on electricity alone, which is seen as a huge appeal to many motorists.
A plug-in hybrid has a much larger battery, which can be charged via a public charger, a home wallbox or a domestic plug socket. Once fully charged, the journeys you can complete in pure EV mode are much longer, before the fuel-powered engine has to turn on to help power the car.
Like most hybrids, a plug-in hybrid can operate using only electric power, just the conventional engine, or a combination of both, providing extra power for things like overtaking or joining a motorway when extra acceleration is required.
Even though a hybrid’s petrol or diesel engine will produce emissions when it is running, the car’s overall emissions are low because the car will defer to electric-only mode whenever possible, when it produces no emissions at all. It generally does this at slow speeds, such as in city centres, stop-start traffic and car parks.
For faster speeds, the combustion engine takes over, as the power required would drain the battery pack too quickly. It will also assume command when battery charge drops below a certain level, even if only driving at slow speeds, and will charge the batteries at the same time until there’s enough electric power available again.
What is a range-extender hybrid?
In many ways a range-extender hybrid is more comparable to an electric car than a hybrid. The best description of a range-extender is an electric car with an on-board power station. You use it in the same way as an electric car, charging it overnight as needed for use the next day. However, you’re not limited to the range dictated by the level of charge in its battery pack. The power station – usually a small petrol engine – is on high alert, ready to charge the battery pack if its charge drops below a certain level.
Although range-extenders are typically classified as hybrids, the following distinction needs to be remembered. All hybrid cars will, at some point, use their conventional engines to provide propulsion, whereas most range-extender cars cannot.
One example of a range extender is the now-discontinued BMW i3 Rex – essentially an i3 electric car fitted with an auxiliary engine under the rear boot floor to provide electricity, increasing its range beyond the limits of its battery. While vehicles of this type typically use electricity alone to operate, the small fuel tank will need filling up from time to time as a backup.
You can read more about range-extender cars in our separate guide.
Plug-in hybrid running costs
Company-car users in particular would be wise to consider a plug-in hybrid for their next car, and the reason for that is down to the way carbon dioxide (CO2) emissions are measured.
As you may know, company-car tax, or Benefit-in-Kind (BiK), is levied according to a car’s CO2 emissions. The lower these emissions, the lower the car’s tax liability. We go into greater depth in our feature that explains what fuel economy figures mean to you, but the upshot is that plug-in hybrid cars tend to do extremely well in fuel-consumption tests.
This is purely because a plug-in hybrid can be expected to run in electric mode for much of the official test cycle, and when using the power in its batteries, it produces no CO2 at all. This means that plug-in hybrid cars frequently emit under 50 grams per kilometre (g/km) of CO2 in official tests, which is the upper limit of the lowest Benefit-in-Kind bracket of 10%.
The importance of this to company car buyers can’t be overstated. Put simply, a car in the 9% BiK bracket will potentially cost half as much in company car tax as one in the 19% bracket.
Of course, BiK is based on the taxable (P11D) value of a given car. And, while it’s true that a plug-in hybrid usually costs more to buy than a petrol or diesel model, most will cost you substantially less in annual company-car tax than a pure petrol or diesel-powered equivalent.
If you’re not a company-car driver, you could still be quids in if your usual daily drive largely consists of low-speed, urban motoring. Crowded city streets are where plug-in hybrid cars really come into their own – if your daily commute is made up of stop-start driving and totals less than 30 miles or so, you may be able to make the journey without using the petrol engine at all. This means you can rely on cheap electricity, rather than pricey petrol or diesel.
However, the more you regularly do higher speeds and longer journeys, the more the petrol engine in a hybrid will be called upon. A long motorway journey in a plug-in hybrid may use more fuel than the same trip in a modern diesel car, and one of the primary reasons for this is the added weight of the electric motor and battery.
To conclude, a plug-in hybrid’s ability to save you money is skewed heavily in favour of company car users, but urban-living low-mileage private buyers may well see the benefits as well.
Disadvantages of plug-in hybrid cars
While regular hybrid cars tend to be more expensive to buy than their petrol-powered equivalents, the same is even more true of plug-in hybrids. Much of the increased cost is due to a more powerful, higher-capacity or more advanced battery than those used in regular hybrids. There’s also extra equipment required for charging directly from the mains and there may be higher manufacturing costs to produce the car in the first place. This means that the added technology and complexity of a plug-in hybrid will usually make it more expensive to buy than a normal hybrid.
It’s worth remembering, though, that you’ll need access to a mains supply or fast charger close to where you regularly park in order to charge your plug-in hybrid. Although the national electric car charging infrastructure is rapidly expanding, you may find overnight or daytime charging tricky to achieve if you find it difficult to park outside your house or office for more than a couple of hours, and even trickier if you live in a flat without the right infrastructure in place.
Plug-in hybrids may also be slightly compromised where practicality is concerned in comparison to their conventional counterparts. This is because the large battery pack is usually placed below the boot floor, affecting boot space.
Plug-in hybrids: range
Just how far a plug-in hybrid car can travel – known as its range – in electric-vehicle (EV) mode alone varies from car to car. However, with the option to fully charge the battery from a mains supply before you embark on your journey, you’ll be able to drive further than in a regular hybrid before the battery needs topping up, either from the engine cutting in or when you next plug it into a mains supply.
For example, the plug-in BMW 330e has a range of around 30 miles in all-electric mode. This is enough to cover many drivers’ morning commute, with the petrol engine boosting the battery in higher-speed parts of the journey and electric power alone in stop-start traffic. It’s in these slow-moving, congested areas where low emissions are particularly valued.
The difference between a regular hybrid car and a plug-in hybrid is highlighted when you look at the Toyota Prius. The normal Prius hybrid’s all-electric range is only 0.6 miles. This doesn’t sound like a lot but, if the Prius spends most of its life making low-speed urban journeys in heavy traffic – which is what its designers intended – its electric motor may be operating as much as 70% of the time.
With the Toyota Prius Plug-In, reliance on the petrol engine is reduced still further. With the facility to fully charge the battery pack from the mains, the Prius Plug-In has a longer claimed all-electric range of 31 miles if the batteries are fully charged, with a full charge taking two hours. This longer range enables more of each journey to be made without help from the petrol engine, further reducing average CO2 emissions.
Plug-in hybrids: battery life
As with electric vehicles, a common fear when it comes to hybrids is battery life. As anybody with a mobile phone or a laptop computer knows, battery performance inevitably degrades over time. To counter this, some hybrid cars come with a warranty that specifically covers battery degradation.
For instance, Kia outlines its expectations for the battery life of its plug-in hybrid model range within the careful wording of its policy: "The Lithium-Ion Polymer Battery warranty covers a minimum capacity for a period of 84 months or 100,000 miles from the date of first registration, whichever comes first. This warranty covers repairs needed to return the battery capacity to at least 70% (65% for cars shipped after 1 August 2019) of the original battery capacity. Where possible, the original EV battery components will be repaired and will be returned to the vehicle. If unrepairable, the: EV/PHEV Battery will be replaced with either a new or remanufactured Lithium-Ion Polymer Battery.”
It’s worth remembering, though, that hybrids car battery packs are specifically designed to survive any demands that could be reasonably expected from the vehicle. Toyota, for example, states that its hybrid and plug-in hybrid battery packs are intended to last the lifetime of the car. The standard battery warranty covers five years or 100,000 miles, with Toyota also offering Hybrid Battery Extended Cover, which adds an extra year or 10,000 miles of coverage. This can be renewed up until the car is 15 years old, with no restriction on the total mileage.
For its older hybrid models, Toyota also has a clause in its warranty that specifically states the cover provided for a battery pack, with the duration of warranty cover depending on when the car was built. For example, cars registered between 1 June 2010 and 31 March 2014 enjoy an eight-year/100,000-mile warranty specifically for their battery packs. It’s therefore worth checking with your dealer exactly what the battery warranty period will be for your particular car.
What plug-in hybrid cars are there to choose from?
Most manufacturers now offer electric or hybrid versions of at least one car in their range, and many are now introducing plug-in technology, too. Plug-in hybrids come in all shapes and sizes; from family hatchbacks to large SUVs, there will be something to suit your lifestyle.
While the Mitsubishi Outlander PHEV was one of the very first plug-in hybrid SUVs, it now has a long list of rivals including the Kia Sportage plug-in, Ford Kuga PHEV, MINI Countryman, Peugeot 3008 Hybrid and the Hyundai Tucson plug-in hybrid.
Audi offers e-tron plug-in hybrid variants of its A6, A7 and A8 models and across its SUV range, including the Q5, Q7 and Q8. For those looking for a slightly smaller package, Audi has also hybridised its A3 and Q3 models.
Volkswagen has plug-in hybrid GTE versions of its Golf and Passat models, both of which share the practicality, comfort and styling of the cars they’re based on. It’s worth bearing in mind that they both have slightly less boot capacity than their conventionally powered equivalents because the batteries for the electric motor take up some of the luggage space. More recently, Volkswagen has also released hybrid versions of the Arteon, Tiguan and Touareg models.
Mercedes-Benz has arguably done the most work in offering plug-in hybrid technology across its range, with no less than 19 PHEV options across its lineup at the time of writing. Such examples include the Mercedes A-Class A 250 e, the Mercedes E 300 e and E300 de hybrid models and the Mercedes GLE 350 e SUV.
The BMW 330e is a plug-in hybrid version of the successful BMW 3 Series compact executive saloon, with average emissions stated as below 50g/km and a claimed fuel economy of over 200mpg. It’s available alongside a pair of 5 Series hybrids called the 530e and 545e. BMW also offers the X5 as a PHEV; the xDrive45e model promises over 50 miles of electric range. The X2 xDrive25e and 225xe Active Tourer models are other options customers can choose from.
Plug-in hybrid government grants
There is no longer a plug-in grant from the UK government after the initial £2,500 grant scheme was axed in 2018. A second plug-in car grant (PiCG) for fully electric vehicles introduced in 2021 for vehicles costing less than £32,000 was then removed in June 2022 and did not apply to plug-in hybrid vehicles.
Although there is no longer a grant for the purchase of electric vehicles or plug-in hybrids, a grant for a home charging point remains for people living in rented accommodation and homeowners who live in flats with dedicated off-street parking. Up to 75% of the cost of buying and installing a home charge point, up to a maximum of £350, can be claimed from the government-backed initiative EV charge point grant scheme.
If this all sounds too good to be true, it is, because to qualify for this scheme, you must fulfil the following strict criteria: You must own one of the eligible cars for the subsidy from the current list here.
- Only those living in flats or rented accommodation may apply - homeowners living in single-unit properties such as houses and bungalows are no longer eligible as of March 31 2022.
- Applicants must have dedicated off-road parking at their flat or rented property.
- Owners must be able to prove ownership of an eligible car, or that an order has been placed for an eligible model for delivery within four months of the installation date of a charger.
However, unlike the now-discontinued Electric Vehicle Homecharge Scheme, EV owners will not be able to claim the grant for a second EV charger if they own another electric vehicle.
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