It turns out that plug-in hybrid cars are capable of emitting up to three times more carbon dioxide in the real world compared to advertised figures, and some of the cars are even more polluting than lighter petrol vehicles, the Daily Mail reports.

The primary reason for this is because hybrid and plug-in hybrid cars are normally heavier than their petrol counterparts due to the extra weight incurred by having an electric motor and battery pack. This is on top of the fact that PHEV owners sometimes neglect to charge their vehicles, thus losing the benefits of electrification.

The findings come in the wake up the UK government’s plan to hasten the ban on the combustion engine – including hybrid cars – by 2035 (five years quicker than the initial 2040 target). The same series of studies also showed that fuel consumption rates of electrified vehicles are far greater in the real world than in testing conditions.

Transport team leader from the Committee on Climate Change, Ewa Kmietowicz said: “When charged appropriately, plug-in hybrid vehicles allow drivers to complete the majority of trips in all-electric mode. However, there is a concern that PHEVs are not being used as intended, achieving less than one-third of miles in electric mode, and risking higher emissions.”

“By the end of the year, most new models of fully electric vehicle will be able to cover 150 miles (240 km) on a single charge, and the need for plug-in hybrids will inevitably decline,” Kmietowicz added.

A study conducted by The Miles Consultancy, a fuel management firm, found that vehicles produced by BMW, Mercedes-Benz, Mitsubishi, and Volkswagen often returned fuel consumption figures that are up to three times higher than advertised. In fact, 187 regularly-charged BMW PHEVs were audited, and the average fuel economy is only 42 mpg (6.7 litres per 100 km) versus the claimed figure of 137 mpg (2.1 litres per 100 km).

PHEV researches in Norway also did a study in 2018, which found that the average yearly estimated CO2 emission was about 2.5 times higher in the real world, when compared to the value stated in the type approval test, the Telegraph reported.

Plug-in hybrid sales have proven to be popular in recent years, and the numbers will continue to grow. In Europe, for example, analysts predict that sales of PHEVs will increase from 220,000 to 590,000 units this year, partly driven by tax breaks offered to company car owners. In other parts of the world, “greener” cars also benefit from tax breaks as incentives to spur motorist interest.

Experts such as Paul Hollick, the managing director of The Miles Consultancy, questioned whether some plug-in hybrid cars ever get to see a charging cable. “In a lot of cases, we see PHEVs never being charged, doing longer drives and this is not a good fit for a lot of car users,” he said.

One of the UK’s most popular electrified cars is the Mitsubishi Outlander PHEV, but Emissions Analytics boss Nick Molden said “the problem is the official figures are very sensitive to assumptions about how PHEVs are being charged and driven.”

A Mitsubishi spokesperson later said the Outlander PHEV was originally tested for emissions and fuel economy in a fully charged state. “We state in our promotional material that the official figures are only for comparison to similar vehicles and that they may not reflect real-life driving results,” the person added.

Based on Emissions Analytics’ survey, 96% of Mitsubishi PHEV owners claim to charge their cars at least once a week, while 68% said they recharge their cars on a daily basis. Well, if you own a plug-in hybrid car, we suggest charging it whenever and wherever possible.

Closer to home, statistics show that while there are around 5,000 ChargEV members in Malaysia (registration for the local charging network is free, and a membership is provided with every purchase of a BMW PHEV), less than half of them use the chargers regularly. That’s not exactly a stellar figure, especially as Malaysia is a big market for premium PHEVs.

So remember, guys. It’s one thing to buy a plug-in hybrid, but you won’t do anyone any good if you don’t charge it. The weight penalty of a PHEV is significant and, unlike a non-plug-in parallel hybrid, these cars are not designed to be driven without being charged, so petrol-only running is highly inefficient and you’ll be lugging all that extra weight for nothing. In this case, plugging in really goes a long way.