Are plug-in hybrid cars worse for environment than factory tests suggest? It depends how you drive them

(The Conversation, 21 Sep 2020) Currently accounting for 3% of new car sales, plug-in hybrid electric vehicles are sold as low-carbon alternatives to fossil fuel and conventional hybrid cars. But a new report threatens to shatter their green credentials.

Research from the pressure groups Transport and Environmentand Greenpeace has claimed that CO₂ emissions from plug-in hybrid cars are “two and a half times” higher than tests by manufacturers suggest. While these official figures place the average emissions from plug-in hybrid vehicles at 44g of CO₂ per kilometre, the new report argues that it’s more like 120g on roads.

So why is there such a large discrepancy, and which one is correct? Are customers being misled about the environmental impact of the cars they drive?

How carmakers measure emissions

A plug-in hybrid electric vehicle has both a petrol engine and battery, either of which can power the wheels. Unlike a normal hybrid vehicle, where all the energy comes from the fuel, a plug-in hybrid has a larger battery and can be plugged into the mains to charge. Because a plug-in hybrid has two energy sources, petrol and electric, its emissions will vary widely depending on how much time is spent in full electric or petrol mode.

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The Conversation, 21 Sep 2020: Are plug-in hybrid cars worse for environment than factory tests suggest? It depends how you drive them