By Bryce Gaton

First published on, December 2022.


Plug-in Hybrid Electric Vehicles (PHEVs) have often been touted as a stepping stone in the move from fully fossil-fuelled vehicles to fully electric ones. However, there is a problem with this view of PHEVs. Studies are now showing that their real world CO2 performance falls far short of what is expected from the official figures derived through the mandated European WLTP test cycle.

When it comes to PHEVs, how much CO2 is saved by switching from pure internal combustion engine (ICE) cars to PHEVs depends on two things:

  1. the percentage of kilometres driven in ‘EV only’ mode and
  2. how that electrical energy is sourced.

Percentage of kilometres driven in EV mode:

Recent real-world testing data from Europe shows that PHEVs are driven in ‘EV only’ mode much less than what is assumed through the WLTP test cycle used to come up with the official CO2 figures. It should therefore not come as a surprise that the real-world figures for PHEV CO2 emissions are on average 2-4 times higher than their WLTP numbers.

This is not helped by the fact that PHEVs have two drive systems - the extra weight of the electric motor, batteries and electrics means they are heavier than an equivalent ICE car. As vehicle weight is a big contributor to fuel used, a PHEV is likely to use more fuel to lug that weight around than an equivalent ICE-only vehicle.

How that electrical energy is sourced:

Worse still, when the engine is used to both power the car and charge the hybrid battery for later use, as much as 12 times the official CO2 value can be emitted (see graph). This is because charging the battery using the engine is on average three times less efficient than charging from a 240V electricity supply.

If deliberately choosing to charge the battery from the engine rather than a plug (which is selectable in some PHEVs) – then in effect you have achieved ‘the worst of both worlds’.

To quote Julia Poliscanova, senior director for clean vehicles at Transport and Environment:

“Plug-in hybrids are fake electric cars, built for lab tests and tax breaks, not real driving. Our tests show that even in optimal conditions, with a full battery, the cars pollute more than advertised. Unless you drive them softly, carbon emissions can go off the charts. Governments should stop subsidising these cars with billions in taxpayers’ money.”

So where does this leave Australian drivers? Given Australian daily commuting distances are generally higher than European ones – the case for reviewing the status of PHEVs as ‘green’ is even greater than in Europe.

This means that any coming ‘Australian contextualised’ fuel emission standards will need to address this issue. Especially if that system (as expected) includes the ‘teeth’ of manufacturer credits and fines for meeting or missing the targets. Otherwise, giving PHEVs credits for lower emissions than they actually achieve will have the perverse outcome of slowing the adoption of full electric cars and instead encourage the sales of PHEVs into uses that do little to reduce CO2 emissions or fossil fuel use.

It is also worth remembering that a PHEV contains two drivetrains (ICE and electric), meaning the maintenance savings that a BEV offers are lost as the ICE component still needs the usual regular minor/major servicing – along with creating its associated waste stream of oils, filters and other consumables.

As a final note: it is worth remembering still that a PHEV, properly chosen and driven, WILL reduce emissions if driven within the WLTP driving cycle conditions. However the use-case for a PHEV is particular to that individual PHEV model and your individual use case fitting within that driving cycle. Plus, if your use-case changes (such as changing jobs to a longer daily commute that extends beyond the battery range), you will need to review your PHEV choice.

However, a PHEV can work for you IF your use-case includes:

  • using the PHEV most of the time within its EV-only range,
  • ensuring you regularly recharge the PHEV battery before it runs out via a power outlet and
  • if the PHEV has the option to selectively recharge via the internal combustion engine whilst driving, switching that option off unless it is absolutely necessary to use it.