Are plug-in hybrids good for the environment, or just marketing hype?

By Ben Elliston, Peter Campbell
May 22 2024 - 5:30am

Now that the new vehicle efficiency standard has been passed by Parliament, we can expect to see some early shifts in the vehicles on sale in Australia to include models of battery electric vehicles and plug-in hybrid vehicles that have been on sale in overseas markets for years.

As battery vehicle sales have taken off, plug-in hybrids and traditional hybrid vehicles are now being marketed with enthusiasm. Plug-in hybrids are combustion engine vehicles with a medium-sized battery that can be plugged into the mains to give a certain amount of electric operation. These contrast with traditional hybrid vehicles where a small battery can only be charged by recovering energy when slowing down, giving modest fuel savings. Some describe plug-in hybrids as "the best of both worlds" because they can run on electricity for short local trips and on fuel for highway trips. Others describe plug-in hybrids as "the worst of both worlds" - a polluting engine with its higher maintenance costs, and a battery that is too small to save much fuel on long trips.

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Despite hybrids often being described as a "transition technology", they have been around in mass-produced form since the Toyota Prius was introduced late last century. Plug-in hybrids aren't new, either. In the early 2010s, the Australian Electric Vehicle Association was supportive of plug-in hybrids as a semi-electric "stop-gap" that could complete long journeys. That was before we had long-range battery vehicles and fast charging along highways. A decade later, we can skip this step in the transition.

A diligent plug-in hybrid owner may achieve low fuel consumption but it's difficult in practice. One of the authors owned a 2013 Holden Volt plug-in hybrid for several years before replacing it with a long-range battery electric vehicle. Despite always plugging in at home and overnight on multi-day trips, he only managed to average 2.2 litres per 100km, almost double the rated 1.2 litres per 100km. This was because the engine would start 60km into any out-of-town trip and the rest of the day would be petrol-powered. A weekend trip could use as much petrol as was avoided by a month of local electric driving.

Vehicle fuel consumption is tested in Australia using the New European Driving Cycle test. For plug-in hybrids, the test adds only 25km of petrol driving on top of the electric range. This assumes that the vehicle is mainly used for short trips and regularly charged. The government is replacing this test with the Worldwide Harmonised Light Vehicle Test Procedure by 2028. While the new test procedure is regarded as generally producing more realistic consumption figures for other vehicle types, it still significantly underestimates the real-world fuel consumption of plug-in hybrids.

An individual charging their electricity-powered car. Picture Shutterstock
An individual charging their electricity-powered car. Picture Shutterstock

Car buyers are familiar with the discrepancies between the fuel consumption shown on the windscreen sticker and their real-world experience, but these are nothing compared with European studies that showed the actual emissions from plug-in hybrids are, on average, 3.5 times higher than test results. We know this because all vehicles sold in the EU since 2021 are fitted with fuel consumption monitoring. The EU plans to adjust the new test procedure based on these real-world fuel consumption data next year, followed by another revision in 2027. These improvements should bring the rated fuel consumption for plug-in hybrids closer to the disappointing, on-road reality.

The European studies explained the wide discrepancy between tested and on-road fuel consumption. The main reason is that a plug-in hybrid's ability to use petrol provides drivers with less motivation to plug in after every single local trip, which is needed to keep its smaller battery charged. In contrast, the larger battery of a battery electrical vehicle allows less frequent charging. Although the fuel consumption of a petrol or diesel vehicle can vary a little due to lead footedness, the fuel consumption of plug-in hybrids can vary much more because it requires diligence to plug in after every trip (or ever). Even greater fuel consumption was found for company cars where drivers have a fuel card but aren't compensated for the use of their home electricity.

Other reasons for higher plug-in hybrid emissions include some models having a very short electric range or an underpowered motor. An underpowered motor means that the vehicle will start the combustion engine whenever extra power is needed. European clean transport advocacy group Transport & Environment refers to plug-in hybrids as being "built for lab tests and tax breaks". One luxury plug-in hybrid model has a V8 engine and an electric range of just 13km.

European governments are now removing incentives for plug-in hybrids and including them in future combustion vehicle bans in recognition that these vehicles are failing to deliver the expected fuel savings and emissions cuts. Australia must be careful to avoid repeating Europe's missteps. As the government prepares to regulate vehicle CO2 emissions next year, it urgently needs to review its incentives and get the testing of plug-in hybrids in order for the benefit of consumers and the climate.

  • Ben Elliston is the chair of the ACT branch of the Australian Electric Vehicle Association. Peter Campbell is an ACT branch committee member and EV driver of 15 years.