What Is A Plug-In Hybrid?

A Plug-In Hybrid Electric vehicle (PHEV) operates by both battery and fuel – the car will typically run on electric power until the battery becomes depleted allowing the car to automatically switch to fuel to continue the journey whereas a Battery Electric vehicle (BEV) cars operate solely by battery and will need recharged once  the battery becomes depleted. PHEVs can be a good option for anyone who's not ready to go fully electric, because they provide many of the fuel and emissions benefits of electric cars on short drives, but have the back-up of a petrol or diesel engine for longer runs. According to official figures, 66,877 plug-in hybrid cars were sold in this country in 2020 – a massive 91% increase on the previous year. Sales will only continue to rise as we near 2030, when all sales of conventional petrol and diesel cars will be banned.

Plug-in hybrids represent a vital stepping stone between the petrol or diesel cars the vast majority of people drive today and a zero-emissions future. For most owners, the fact plug-in hybrid models can save them money will also help them find favour, with the fact they're also designed to reduce pollution a happy bonus. Like other types of hybrids, a plug-in hybrid has two power sources – an internal combustion engine using petrol or diesel fuel, and a battery-powered electric motor. The engine is the same as that found in regular petrol or diesel cars, while the electric motor is similar to that found in other hybrids and electric cars. 

A plug-in hybrid’s battery can be recharged by plugging it into a power outlet, which is why it’s called a ‘plug-in’ hybrid. Ranges are typically 20 to 30 miles, but some of the latest PHEVs have an official pure electric range of more than 50 miles. This means they can complete shorter urban journeys on electric power, emitting zero tailpipe emissions, but you don’t need to worry about topping the batteries up to complete longer drives because the conventional engine automatically kicks in and takes over the driving when the batteries are depleted. 

Those additional batteries are heavy, so fuel economy when running on the combustion engine may not be as good as that of a non plug-in alternative. To aid weight savings, some car makers choose to fit a smaller than usual fuel tank to their PHEVs, so you may only get 200-300 miles of fuelled range between fill-ups compared with around 500 miles from a non plug-in model.

What's the difference between plug-in and conventional hybrids?

Conventional hybrids work in much the same way as plug-in hybrids but have built-in systems to recharge their batteries, which is why they’re called  ‘self-charging’. You can’t plug them into a power outlet. A plug-in hybrid has a bigger battery than conventional hybrid, which is charged by the car itself when it’s on the move but can also be charged by plugging it into a home, public or work charging point. Plug-in hybrids have a more powerful electric motor than most conventional hybrids, allowing them to go much farther using electric power alone. The ability to cover many more miles using only electric power means that the official fuel consumption and emissions figures for plug-in hybrids are far lower than for conventional hybrids, although you need to keep them charged to get the full benefit.

Plug-in hybrid 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. 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%. 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.

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 can degrade over time. The warranty for hybrid cars may specifically allow for this. 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 01 August 2019) of the original battery capacity. Where possible, the original EV battery components will be repaired and will be."

What are the advantages of a plug-in hybrid?

The main advantage of running any PHEV is that it will have lower CO2 emissions and better fuel economy than a conventional combustion-engined car. The benefits are best if you are able to do shorter journeys using all or mostly electric power, and as long as you remember to charge up the car’s batteries in-between every trip. On average it costs 12p per mile to drive a petrol-engined car, this drops to just 5p per mile for trips done using electric power if you charge up at home at a rate of 14p per kilowatt hour.   

You’ll also benefit from either a lower or zero rate of road tax (VED) compared with internal-combustion engined cars. And, if you live in the city, you could also avoid paying charges for driving your car, such as London’s Congestion Charge (if your car emits less than 75g/km of CO2). Another advantage of both conventional hybrids and PHEVs is that they do away with the ‘range anxiety’ associated with electric vehicles: because there’s also a combustion engine, you won’t suddenly run out of range.

What happens if you don't plug in a plug-in hybrid?

The worst that’ll happen is that the battery will run flat, so you won’t be able to use the electric motor until you recharge it. The car will still be perfectly drive-able because it can use its petrol/diesel engine instead. The car’s built-in power generation systems generally prevent the electric motor’s battery from running flat, but there are some situations where it might happen – on a long motorway drive, for instance.

What's it like to drive?

When the engine’s running, a plug-in hybrid feels the same to drive as any other petrol or diesel car. When it’s running on pure electric power, it feels like an electric car – which can be a little eerie if you’ve not experienced one before because there’s so little noise and most accelerate very quickly and smoothly from a standstill. The way a plug-in hybrid’s petrol or diesel engine starts up and shuts down while driving, often seemingly at random, can seem a bit strange at first, too. The brakes also take a bit of getting used to, and it’s worth noting that some plug-in hybrids are very fast. Indeed, the fastest version of some cars are now plug-in hybrids.

Are there any disadvantages to a plug-in hybrid?

A factor in the discrepancy between the official and real-world fuel economy is that plug-in hybrids can use more fuel than you might expect when running on the engine alone. The batteries, electric motors and other components in the hybrid system are heavy, so the engine has to work harder, and use more fuel, to move it all. Plug-in hybrid cars also cost quite a bit more to buy than the same car with a petrol/diesel engine. And, as with an electric car, if you live in a flat or house without off-road parking you might not be able to install a home charging point.

Check out our page on electric and hybrid vehicles with more information, or you can contact us directly with any questions - we'd love to hear from you.