I spent some time in a Mercedes S-Class plug-in hybrid, recently. I know… humble brag, right?
It was precisely the ambient-lit, creepily quiet, massage-tastic, ‘look at my pillowy headrest!’ smug overload that you’d expect. Not to mention a silky in-line six cylinder engine, and a chunky 28.6kWh battery for an official electric range of up to 63 miles. I managed 45 miles on electric running despite being mostly on faster country roads, which is a useful electric range – especially if you’re a chauffeur dealing with a lot of city-based VIP transits, as I’m sure is the default remit for the Merc S580 plug-in hybrid model that I’ve been gracing rural Hampshire with.
But it did get to me to thinking about plug-in hybrid (PHEV) technology. On the one hand, I suspect this tech feels like the no compromise solution for lots of buyers. Especially with plenty of everyday PHEVs now sporting bigger batteries and better range (a Skoda Superb iV PHEV has a claimed EV range of over 80 miles, and is definitely the everyday S-Class, as I’m sure you know).
The figures support the idea that PHEV tech is appealing to lots of people, as UK sales of plug-in hybrids rose by 31.5% in 2024, accounting for an 8% market share.
This is great if it means more miles on electric power, but of course a PHEV only achieves that if people actually plug the car in regularly. A report published by the European Commission last year, taking data from 600,000 cars, suggested that real world mpg and emissions from PHEVs are roughly three times worse than the claimed figures suggest. The average official mpg was 167mpg, while the average real-world mpg was 47mpg. That’s not just the mpg when the engine’s running; it’s the overall average mpg of the PHEV vehicles in question, including the miles done on electric power, over a year of driving.
The good news (I think?) is that non-electrified diesel and petrol cars fared worse, returning real-world economy of 41- and 35.8mpg respectively – albeit the gap between these figures and the respective official claimed economy was vastly smaller.
Personally, I’m eye-rollingly unsurprised at this news, as official WLTP tests currently put unrealistic weighting on the electric running potential of PHEVs, resulting in wildly optimistic official figures. That’s no doubt a big part of these findings, which is why with a PHEV you should just ignore the claimed numbers. And it’s worth noting that changes are coming to the WLTP testing on PHEVs, which will hopefully improve the situation.
But I do wonder how much of this rather disappointing reality check on the real-world efficiency of PHEVs is also down to drivers who are just not bothering to plug them in.
Here’s the issue: if people are buying PHEVs because they’re convenient, and/or because they’re affordable on company car tax, but they don't regularly charge them, it’s environmental tax breaks without the environmental gains. In which case we’d be better off further incentivising full hybrids (which, annoyingly, weren’t included in the EU commissions survey), very efficient petrol and diesel cars, and efficient EVs. And yes, I said efficient EVs. We really do need to be incentivising miles/kWh (which is like mpg but for electric cars) on electric cars these days, rather than overall range or simply whether it’s zero-emissions or not. Do that, and then let’s see how quickly manufacturers start focussing on efficiency rather than range…
Anyway, I absolutely see the appeal of PHEVs: they offer electric running for your weekly driving, and then no-stress piston power for longer trips at the weekend. And it is no surprise that the S-Class has been an utter joy to spend time with.
But even with PHEV technology improving, I can’t escape the feeling that its days as the stepping stone to full electric power are numbered. And if they aren’t, then they probably should be. If the real-world usage and emissions in the European Commission survey are anything to go by, we’re better off saving the battery resources for BEVs instead.
Ultimately, then, PHEVs seem to be the convenient option as opposed to the environmental one. To me, it would seem to make far more sense to just figure out which works for you – ICE, self-charging hybrid or BEV - and go with that instead.
