Plug-in Hybrid Vehicle – PHEV
PHEVS and EREVS started to appear at roughly the same time, with the Mitsubishi Outlander being the first commercially successful application of the technology, followed by the fleet-friendly Audi A3 e-tron. Since then, though, the vast majority of manufacturers have jumped on the bandwagon, as the tax incentives for running ‘alternatively fuelled vehicles’ have made them irresistible to both fleet buyers and retail customers alike, even though the government pulled the £5000 EV grant from PHEVS in 2019.
They differ from EREVS insofar as the engine has a directdrive connection to the wheels so, when the electric range runs out, the car operates as a normal automatic combustionengined car. Tax changes in 2020 make them less attractive as new cars, but the technology is definitely here to stay.
Indeed, a PHEV is often less efficient than a normal petrol or diesel car when operated in such a way because the extra weight of the EV drivetrain has an impact on fuel economy – but it all depends on how they’re used.
For example, if you have a short commute then the EV range of the car may be sufficient to get you there and back (or almost) on electricity alone, and that obviously makes the overall running costs much lower. If you’re looking to buy one, do your homework because your driving habits will dictate how efficient a PHEV will or won’t actually be. That said, there are road tax incentives, especially on those registered before the 2019 WLTP regulations came in, because they qualify for free VED.
As with EREVS, battery technology is also improving all the time, so ranges are getting longer. The latest models travel up to 40 miles on a full charge, which may not sound much but is more than sufficient for the average urban commuter.
PHEVS work by having two different means of transmitting power, either to the same or different axles. They generally have a battery connected to an electric motor, with the battery being larger than the one you’d get in a hybrid such as a Toyota Prius, or a ‘mild hybrid’, which we’ll come to later.
A PHEV’S battery is charged from the grid, meaning you need to plug the vehicle into either a regular domestic socket, which is perfectly functional for slow overnight charging, or a wall box installed at your house. You can also charge a PHEV using public charging points.
As a general rule, the electric motor does all the driving at slower speeds until the battery runs out, but that’s not a hard and fast rule. For example, if you need to accelerate hard or climb an incline the negative effect it has on the battery’s charge status is less efficient than the internal combustion engine taking over, so it will automatically take over to preserve the battery’s range. It’s clever stuff, but it is reliant on a series of ECUS and, while there have been no notable reliability issues yet, it’s worth considering how these elements may create problems in the future.
As well as when extra power is needed, the internal combustion engine kicks in if the electric motor is too cold or too hot, or when features that draw a lot of power such as the heater or air-conditioning are turned on.
Most also feature regenerative braking, which uses the kinetic energy from the vehicle’s brakes to feed charge back to the battery. It’s not a massive return of energy, but it can add two or three miles to the overall range, especially if you do a lot of driving in traffic.
It can also be difficult to achieve the claimed fueleconomy figures for plug-in hybrids, which frequently run well into three figures. But depending on your driving style, distances covered and how easily you can top the battery up in the evening, you may see closer to 30 or 40mpg.
At home, you can use a standard three-pin socket to charge your PHEV, but this will take several hours. The exact time depends on the size of your car’s battery. Mitsubishi estimates a three-pin socket would take around five hours to top up the battery of an Outlander PHEV, which could well be all you need if you leave the car to charge overnight. Some larger batteries take as long as 14 hours.
Wall boxes and fast public chargers are usually far quicker and you can get a box installed at home for about £500 providing you commit to a specific supplier, while most large supermarkets and motorway services now offer fast charging, which can top up to about 70% charge in just 45 minutes. That may save you a few pennies but with a PHEV it’s never a dealbreaker; a petrol or diesel engine will never leave you stranded.
PHEVS also shouldn’t be confused with mild hybrids, which use a self-charging hybrid system, relying on kinetic energy from the car’s braking system and indeed from its wheel hubs to feed energy into a small battery, which then powers the car at low speeds – on congested city streets, for example. They’re useful insofar as the hybrid system improves overall fuel economy, but they’re not classed as electric vehicles because the battery cannot be charged at home.