Like most of the UK’s 33-million passenger cars, our XC90 is spending more time parked up than it normally would. Local journeys are unusually favourable for a plug-in hybrid, of course, but I’ve picked up enough information to figure out how it compares to the ‘mild hybrid’ B5 diesel it replaced a couple of months ago.
My gut feeling about PHEVs has changed over the years, and for the better. They were unquestionably over-incentivised early on, especially as company cars, and often badly deployed with drivers who should have stuck with a diesel engine. It’s left a lingering stereotype of the “Mitsubishi Taxlander” with an unused charging cable in the boot, and it’s also produced a legacy of data that can look pretty damning as a result.
The newest concerned voice is Transport & Environment, which suggested last autumn that PHEVs are the next automotive industry scandal. Its report cites test data for several big-selling models, alongside aggregated figures from fuel card companies and fleet management suppliers, suggesting plug-in hybrids consume two or three times more fuel than the old NEDC-derived brochure figures. Not great for a relied-on technology.
I’m not about to argue that the XC90 is the last bastion of green motoring, but it seems to me that shock statistics like this are missing the wider point. Taking the B5 as a baseline, it averaged 34.6mpg in my tenure. That’s respectable efficiency for a high-performance, seven-seat, four-wheel drive SUV. It’s also better than the T8, which I’ve found gets through a gallon of petrol every 25 miles or so once the electric vehicle range is depleted, despite regularly shutting the engine off under gentle driving.
However, the comparison isn’t as straightforward as it seems. Let’s assume the T8 returns 25mpg, alongside the 21 miles I’m getting to a full charge. That would make the hybrid more fuel efficient than the diesel for any journey under 75 miles. And because petrol is cheaper per litre, the T8 only needs to do an unambitious 25 per cent of its annual mileage in EV mode to match the fuel costs of its diesel counterpart.
Of course, electricity also costs money; 16p/kWh according to the latest BEIS figures. The XC90 travels about two miles per kilowatt-hour put into the battery, which halves the cost of my local driving, but the diesel breaks even 50 miles into a journey. The T8 would need to complete around 42 per cent of its annual mileage on battery power to match the diesel’s fuel costs. That won’t suit everyone, but it’s also not unrealistic.
My point is, if a PHEV uses three times more fuel than advertised, then that’s often in line with what you’d get from a diesel anyway. The difference is the hybrid can do all of its local journeys on battery power, and that’s where it’s most important. Even without the unusually favourable conditions, that feels like a step in the right direction to me.
Date arrived 8th December 2020
Economy (WLTP combined) 83.1 to 100.9mpg
Economy (On test) 64.6mpg