Plug-in hybrid (PHEV) vs hybrid power: which is best for me?

Want a part-electric car but don't know whether a standard hybrid or plug-in hybrid (PHEV) is best for you? Here's how the numbers stack up

Joe Holding
Nov 11, 2020

An increasing number of cars are adopting hybrid technology in order to become more fuel efficient and meet the latest targets for CO2 emissions. This is great news for those who want to cut their fuel costs and potentially save an enormous amount of money in running costs over the lifetime of a car.

However, such high-tech machines are often very expensive brand new compared with conventional petrol and diesel models. Thankfully, more and more used hybrid and plug-in hybrid models are available, bringing them in reach of ever more drivers. But, would a hybrid or plug-in hybrid work for you? Keep reading to find out.

If you’re not familiar with the latest developments, the amount of jargon attached to current tech can be off-putting. What exactly is a mild hybrid? Are PHEVs better than conventional hybrids - also known as 'self-charging' hybrids? Which will cost less in fuel? These are just some of the questions you're likely to want answered.

To help you get your head around it all, we’ve put together the following guide. Later on we’ll compare hybrids directly with PHEVs to give you an idea of which will suit you most, but first let’s explore the different types of hybrid in detail.

Mild hybrids

Mild hybrids are the least sophisticated type of hybrid: most use a small 48-volt battery to collect energy that would otherwise be lost when slowing down. This energy then feeds an electric motor, which can help a petrol or diesel engine to accelerate more efficiently. Crucially however, a mild hybrid cannot travel using just electric power - you simply get a small electric boost rather than the motor being capable of powering the car by itself.

The other way in which mild hybrids save fuel is by switching the engine off when you come to a stop. The extra capacity of the starter-generator means petrol and diesel engines can typically be left to idle for longer than cars with ‘start-stop’ technology, meaning less fuel goes to waste.

Full or ‘self-charging’ hybrids

Full hybrids usually have a slightly bigger battery than mild hybrids, with an electric motor that allows a very limited amount of zero-emission driving using electricity alone; usually no more than a mile. Most full hybrids gather electrical energy in exactly the same way as mild hybrids, although some can also generate electricity directly from the engine.

Full hybrids usually offer marginally better fuel economy than mild hybrids, although they tend to be more expensive too. Toyota and Lexus describe their full hybrids as ‘self-charging’, however this is just a marketing ploy designed to highlight that these cars don’t need to be plugged in.

The reason they don't need charging is because their batteries are far smaller than the ones that come with plug-in hybrids, so you get much less electric range. If you want the greatest electric range and are happy to plug in the car regularly - but don't want a fully electric car - plug-in hybrids offer a much greater electric range, allowing you to complete shorter journeys solely on electric power.

Plug-in hybrids

PHEVs (or plug-in hybrid electric vehicles) have much larger batteries than those of mild and full hybrids (although they still use far fewer cells than electric cars), so much so that the only practical way of charging them is via a cable. PHEVs can be plugged into a dedicated home charger or if need be, a standard three-pin socket (which is the slowest charging option) or you can use public chargers. A full top-up from empty normally takes a few hours - longer when using an ordinary socket.

Most plug-in hybrids can travel 20-30 miles on electric power alone, although there are some newer models that can do more than 40. Once you’re out of juice PHEVs will revert to running on their petrol or diesel engines like a normal car, while still using that extra battery capacity to recycle electricity like full hybrids - providing a slight economy boost.

Charge a PHEV regularly and only cover short trips and all of your journeys could be on electric power (though if this is the type of driving you do, it would make sense to consider a fully electric vehicle rather than lugging around a redundant petrol or diesel engine). If you're deliberating between a PHEV and a fully electric vehicle, read our guide to plug-in hybrids versus electric cars. Fail to charge the car regularly with a PHEV, however, and you may as well get a cheaper standard hybrid.

PHEV vs hybrid: which is best?

In order to work out which type of hybrid will work best for you, you need to understand what their strengths and weaknesses are. Then you need to weigh up those pros and cons against how much you will pay: generally speaking, the more advanced the technology, the more it’ll cost you.

You also need to consider where you would charge a plug-in hybrid and whether you'll be disciplined enough to actually plug it in regularly. Either you’ll need private off-street parking where you can install your own charging point, or access to a charger at your place of work. It’s unrealistic to rely on public charging points to run a plug-in hybrid due to the amount of time it takes to charge the battery.

For mostly short journeys...

If most of your journeys are relatively short - say a 15-mile daily commute, or trips between your home and the supermarket - then a plug-in hybrid is likely to save you more money in the long run - if you make sure to charge the car regularly. This is because it’s much cheaper to drive using electricity than it is using petrol or diesel.

Take the Toyota Prius Plug-in as an example: it has an 8.8kWh battery that allows it to drive up to 34 miles on a full charge before needing to switch the engine on. On a standard electricity tariff, a full charge should cost around £1.20, or less than 4p per mile. So, the more you can charge up between trips, the more money you’ll save on running costs.

Don’t be fooled by the official fuel economy figures for plug-in hybrids though (up to 217mpg in the case of the Prius Plug-in): these assume that you’ll start every journey with a full battery, which isn’t realistic in practice. Having said that, if you’re disciplined with charging, there’s no reason why you shouldn’t see more than 100mpg, which is a figure no conventional car can get close to.

There’s also a full hybrid version of the latest Prius: this will return as much as 68mpg, which is still very respectable for a car that you can’t plug in. If you know roughly how far you drive annually, you can use these figures to estimate how much you’ll spend on fuel.

Then you need to factor in the purchase price. If you were looking at brand new cars you’d pay almost a £6,000 premium for the PHEV version of the current Prius over the standard hybrid, but this gap comes down massively on used cars over a year old. On BuyaCar a 2018 Prius Hybrid in Excel trim with 10,000 miles on the clock can be secured for as little as £215 per month, while the Plug-in variant isn’t much more expensive.

This isn’t always the case though. 2019 versions of the Hyundai Ioniq Hybrid cost from around £17,000 on BuyaCar, while used examples of the Plug-in version start beyond £20,000. With that in mind, if you have a couple of plug-in hybrid and full hybrid models in mind, it's worth looking at all the prices - or monthly figures if you're planning to finance the car (making sure to get quotes with the same type of finance, deposit, mileage allowance and contract length for a fair comparison) - to see which offers you the better value. 

For mostly long-distance journeys...

If most of your journeys are longer distances, then the advantage of a PHEV over a full hybrid becomes less clear cut. This is because the proportion of time you spend driving on electricity will be less, and when the battery runs out of power it largely becomes a dead weight - as you have to lug around all this extra weight without much electric boost. Imagine the amount of extra effort needed to go for a run wearing a heavy rucksack compared with going running without one - the extra effort for the car to carry this weight means worse fuel economy.

Some PHEVs allow you to completely charge the battery off the engine, however this makes the engine far less efficient and you’ll use more fuel overall. This is an expensive and an unenvironmentally friendly way to charge the car; it's far better to plug in the car to top up the batteries.

For occasional long-distance trips the limited electric range of a PHEV isn’t a problem, but if you rack up serious motorway miles over the course of a year you’ll have to think hard about whether a plug-in hybrid is right for you. If you know you’ll have access to a charging point at, say, an overnight stopover, the fuel economy might still work out better than a full hybrid. If not, perhaps a PHEV isn’t the right choice.

Since many electric cars are now capable of more than 300 miles per charge, you may still want to consider a fully electric car even for longer trips - provided you don't expect to cover many hundreds of miles without stopping. Our guide to PHEVs versus BEVs - that's battery electric vehicles, eg. fully electric cars - should give you a good sense of which option is best for you.

Although full hybrids can’t go very far on just electricity, the hybrid system itself will be much lighter than that of an equivalent PHEV. This means you’ll be slightly more efficient running on the engine alone, and you’ll still get some of the limited benefits hybrid technology can offer. If regularly charging a PHEV sounds impractical (or indeed, a hassle), then a full hybrid might be the more pragmatic way to go.

 

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