The real-life costs of fuelling a PHEV

The real-world fuelling costs of these PHEVs are £672 a year higher than their electric equivalents.

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Plug-in Hybrid Electric Vehicles, or PHEVs, are cars that feature both an internal combustion engine and an electric power train. Unlike other hybrid vehicles, PHEVs have a comparatively large battery that can be charged up using an external source of power, such as a home or public charger, just like a Battery Electric Vehicle (BEV).

We looked at the top 10 selling PHEVs in the UK in 20234. We took their claimed miles per gallon figures, and used the average gap identified in the European Commission report between a manufacturers’ claimed fuel economy and the real-life economy of the PHEVs it produces to identify their real life mpgs. We used this to calculate the cost of the fuel they would have to burn in the real world to drive 8000 miles. We then calculated how much electricity from the grid those PHEVs are also likely to consume in driving that distance, using the 27.6% figure from the European Commission for how much of a typical PHEV’s movement is done using electricity from the grid.

Adding those figures together allowed us to calculate a total, real-life fuel cost for these PHEVs. We then identified an equivalent petrol and electric vehicle for each of these top 10 selling PHEVs, calculated their respecting fuelling costs to travel 8,000 miles, and worked out the difference.

Key findings

  • The UK’s best-selling PHEVs cost, on average, £500 more to fueleach year than their manufacturers claim.
  • Manufacturers’ claims about these PHEVs’ fuel efficiency imply that they will save their owners on average £1,092a year in fuel costs compared to the real-world costs of equivalent petrol cars. In reality, the savings are only just over half that amount, at £593a year.
  • The real-world fuelling costs of these PHEVs are £672 a year higher than their electric equivalents.
  • While switching from the petrol equivalent of one of the UK’s best-selling PHEVs to that PHEV will save its owner £593 in annual real-life fuelling costs, switching to the electric equivalent will save its owner £1,264 – more than doubling the savings.