What is a plug-in hybrid?

  • What is a plug-in hybrid electric vehicle (PHEV)?
  • Parkers explains this popular powertrain tech
  • How does it work and should you buy one?

A plug-in hybrid electric vehicle, PHEV or simply plug-in hybrid, is an evolution of a regular self-charging hybrid. With a larger battery pack and a charging socket, you can top their onboard batteries up from the mains, giving them the capacity to run for several miles on electric power alone.

With most PHEVs offering around 30 miles of range on a full charge, this gives them the potential to act as a full electric vehicle for most people’s daily commutes, but with a standard combustion engine waiting in the wings for the occasional longer journey.

If you want to read more about traditional, self-charging hybrids, click here, or click here to read about mild hybrids.

> What is a mild hybrid?

> What is a self-charging hybrid?

How does a plug-in hybrid work?

On a basic level, a plug-in hybrid works exactly the same way as a self-charging hybrid. It uses two power sources – a petrol or diesel engine, and an electric motor plus battery pack. The car is capable of shuffling between these power sources to maximise fuel economy, and the petrol engine can act as a generator to recharge the batteries. Energy lost under braking is also fed back into the batteries.

The difference is in those batteries – they’re much larger on a plug-in hybrid than they are on a self-charging hybrid, and that’s so that the car can have drive as a pure electric vehicle for much further. Whereas most self-charging hybrids only have a couple of miles of all-electric range, plug-in hybrids usually are capable of around 30 miles.

Mitsubishi Outlander PHEV

They also naturally feature a charging socket and all the hardware on-board to charge up, either from the mains at home or a public charging station while you’re out and about.

Plug-in hybrid pros and cons

The pros are obvious – running costs. Most daily commutes can be achieved on electric power alone, meaning that during the week you might be able to run a PHEV without ever touching expensive petrol or diesel. Using cheap, overnight electricity tariffs to charge up can bring your running costs down to just a few pence per mile.

Even longer journeys benefit from the larger battery pack, as you’re able to save your electric power for where it will make the most difference – in stop-start traffic around town, for example.

Compared with pure electric cars, though, plug-in hybrids don’t suffer the same feeling of range anxiety – as once your electricity runs out, you’ve the backup of a petrol or diesel engine ready to kick in whenever it’s needed.

These twin power sources mean PHEVs return truly staggering numbers. Official mpg figures are often in the hundreds, while CO2 emissions are likely to be under 50g/km. This not only qualifies them for cheaper first-year road tax, but exempts them from London’s congestion charging zone – potentially saving hundreds of pounds per year if you regularly commute into the capital.

Citroen C5 Aircross

They’re not the be-all and end-all, however. PHEVs are excellent for some scenarios, but in others they’re actually inferior to their less sophisticated rivals. Case in point when it comes to doing regular longer journeys. After the first 30 miles or so, when the electric power has run out, a PHEV simply becomes a regular hybrid car – but one that’s burdened with a very large, heavy battery pack. This means fuel economy figures will tumble to well below even what a conventional diesel car could achieve.

With price tags far higher than a self-charging hybrid and, in some cases, knocking on the cost of a full electric vehicle, it’s also worth questioning whether you really need a combustion engine as a backup, or whether it’s time to take the plunge and go for a totally electric car.

Further reading:

> The best hybrid cars to buy

> The best hybrid SUVs

> The best electric cars