Independent, Expert EV Reviews & Advice Since 2006
BMW 530e Hybrid controls 3

How to drive – and design – plug-in hybrid electric vehicles

We’re in a period of transition from petrol and diesel cars to electric cars. Battery electric vehicles are the end goal, but on the journey, plug-in hybrid electric vehicles (PHEVs) offer a stepping-stone between petrol and electric technology. Based on the government’s announcement in November 2020 it’s expected that PHEVs can still be sold as new cars in the UK until 2035.

Most PHEVs have the potential to deliver over 100 miles per gallon, and to significantly reduce emissions, but as a driver, how do you ensure your PHEV is being driven with maximum efficiency? And how should manufacturers design PHEVs to make them user-friendly for consumers to minimise fuel use, lower emissions, and save money? PHEV operating systems are becoming increasingly sophisticated but complex, is this leading to unnecessarily high emissions in real-world use?

Audi A3 PHEV screen 1

Operating PHEV drive modes – screen 1

Audi A3 PHEV screen 2

Operating PHEV drive modes – screen 2

Even up to this point, PHEVs have had a bad press, primarily due to some company car users choosing plug-in hybrid technology to benefit from low Benefit in Kind rates, and therefore significant tax savings, and then never plugging the cars in. The result of this is that many PHEVs are driven around the country on their petrol (or occasionally diesel) engines rather than on electric power. This means that the petrol engine is having to propel the vehicle – including the extra weight of the PHEV’s battery and electric motor – resulting in a PHEV running solely on its petrol engine being less efficient than a petrol car.

Audi A3 PHEV screen 3

Operating PHEV drive modes – screen 3

Audi A3 PHEV screen 4

Operating PHEV drive modes – screen 4

Most plug-in hybrids offer the option to choose electric, petrol or hybrid power – the latter using a combination of the petrol engine and the electric motor. A PHEV should be used primarily on electric power for journeys of around 20-30 miles between charges (although increasing numbers of the latest PHEVs have electric ranges of over 40 or 50 miles), with occasional use on longer journeys. With such a driving pattern, a plug-in hybrid could average over 100mpg in the real-world. This may not match the 200mpg+ official economy figures of many PHEVs, but this is still better than the 30-40mpg that a petrol car might achieve – and critically, a PHEV should be driven on zero tailpipe emission electric power in local built-up areas.

BMW 530e Hybrid controls 1

Operating PHEV drive modes – buttons

BMW 530e Hybrid controls 2

Operating PHEV drive modes – screen 1

But there’s a problem. To achieve over 100mpg from a PHEV, you need to drive on electric power for as much time as possible. You also need to choose electric power at the right time – such as for urban driving – and if on a longer journey, choose petrol power at motorway speeds. Although some PHEVs are claimed to intelligently switch between petrol and electric power automatically – more on that later – in reality getting the best from a PHEV in terms of minimising emissions requires active input from the driver. If a PHEV isn’t used on electric power at the appropriate time, and if it isn’t used on its petrol engine at the appropriate time, then fuel consumption and emissions increase.

BMW 530e Hybrid controls 3

Operating PHEV drive modes – screen 2

BMW 530e Hybrid controls 4

Operating PHEV drive modes – screen 3

To help drivers, car manufacturers need to make it easy for people to drive PHEVs in the most efficient way. This means that it must be straightforward to select electric or petrol power. To achieve this, the easiest solution is a big clear button to select electric power, and a big clear button to select petrol power. Such a system exists in the Mitsubishi Outlander PHEV – there’s a button for electric power, and there’s a button to save the battery charge – in other words by choosing to drive using the petrol engine. You can also select the option of charging the battery from the petrol engine when driving. There are further buttons for Sport, Snow and for all-wheel drive lock.

Mitsubishi Outlander PHEV buttons 1

Mitsubishi Outlander PHEV – EV and Save/Charge buttons

Mitsubishi Outlander PHEV buttons 1

Mitsubishi Outlander PHEV – Sport and Snow/all-wheel drive lock buttons

This solution is effective but not very elegant; unfortunately, the current fashion is for car designers to dislike physical buttons in the interior, and most controls are being placed in a touchscreen – resulting in the controls to allow the driver to adjust the PHEV system – and most other vehicle systems – becoming hidden away, as well as becoming increasingly complex. Some PHEVs do have physical buttons to access hybrid drive options, but in some cars the buttons are so small that many people aren’t likely to see them or know what they’re for.

To select battery hold on some PHEV models – ie. when driving on a long motorway journey – you have to go through a process of pressing around four different screens with menus and sub-menus on the touchscreen. Other brands also have sub-menus where you can further adjust the electric, petrol or hybrid settings that you’ve just chosen – such as the percentage of the battery charge that you want to maintain. In our view, this is all far too over-complex – and there’s certainly too much button-pressing – and will result in drivers not knowing how to control the PHEV system to get the lowest emissions from the car.

Some manufacturers claim that their PHEVs will intelligently decide when to use petrol and electric propulsion on a journey entered in the satnav, the aim being that the battery charge will be used up in the most optimal way as you reach your destination, but this throws up a number of issues including that if you get to your destination and there’s nowhere to charge then you’ll have to drive home with an empty battery.

Green Car Guide has reviewed virtually every plug-in hybrid car that you can buy over a period of more than 10 years, yet it’s a challenge for us to discover how the PHEV control system in each new model works. As PHEVs continue to become more popular with mainstream motorists rather than just early adopters, it will be a real challenge for drivers to know how to control the PHEV systems. And this is likely to get worse as the cars enter the second-hand market, when there’s little chance of a briefing from a car dealer or a previous owner.

PHEVs also need a big clear display on the dashboard to show the driver if they’re using electric or petrol power. You’d think that this would be a feature of most PHEVs, but this isn’t the case.

The vehicle should also always start on electric power to try and ensure maximum zero emission-running – again, you’d think that this would be the case with all PHEVs, but it’s not – many fire up the petrol engine straight away and to override this the driver has to select the electric drive mode (and know how to do this).

Many manufacturers are currently massively expanding their ranges of plug-in hybrids. The low official CO2 figures of PHEVs mean that manufacturers benefit from lower fleet average CO2 emissions, so avoiding or minimising fines for excessive emissions compared to European targets. The low official CO2 figures also mean low company car tax rates, but the accusations of high real-world emissions from plug-in hybrids will only get worse as engineers continue to make the PHEV control systems ever more complex and buried in touchscreen sub-menus.

We’ve averaged over 100mpg from many PHEVs, showing that they can be a good solution for some people’s driving cycles. But unless manufacturers make the control systems of PHEVs much more user-friendly for mainstream motorists, going forward it will be very difficult to recommend PHEVs over battery electric vehicles, which don’t need complex operating systems to be understood to ensure driving is on zero-tailpipe electric power.

Paul Clarke

Paul Clarke Green Car Guide

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