I must confess that I have never driven a PHEV. I was seriously considering one recently and attempted to arrange test drives in the Volvo XC40 T5 Recharge and the Ford Kuga PHEV, but poor service at both dealerships meant that neither happened. I did, however, research them in some detail, having watched and read no end of reviews. I must confess that I am somewhat confused now, as some of the comments in this thread are at complete odds to what numerous professional motoring journalists have said and some even seem to defy the laws of physics and science! Or maybe it’s my ignorance!
My understanding of how PHEV’s work, which I am fully prepared to be corrected on, is as follows. I will use a hypothetical scenario of a 250bhp PHEV which has an 80bhp electric motor paired with a 170bhp petrol engine;
To work at their best, PHEV’s need to be fully recharged regularly via the plug in charge lead. The general consensus seems to be that the real world ‘all electric’ ranges are about 20% less than the manufacturers quote. The default drive mode is hybrid, where the car decides when to use the petrol engine, when to use the electric engine and when to use both together. It is only in this latter scenario that the full 250bhp of my hypothetical car is utilised.
However, many people get PHEV’s with the idea of running the car in all electric (only) mode on short commutes and school runs. For this to happen, you switch the drive mode into pure / all electric mode (names vary). This means that the car is running on the 80bhp electric motor only, as it has no benefit at all from the 170bhp petrol motor, which is switched off. It is therefore a physical impossibility for the car to have the same power and performance running on 80bhp as it does on 250bhp. You won’t use any petrol, but your performance is blunted as a result and the top speed is restricted (speed varies by manufacturer but is, I believe, around 70mph). If you want to go faster the petrol engine engages.
In addition to the charge gained from plugging in, the regenerative braking systems on PHEV’s also restore some charge to the battery. As an aside, quite a few reviews suggest that braking in such cars is less smooth and progressive than conventional braking systems and takes some getting used to. There is a third way to charge the battery, which is to switch to the mode where the petrol engine will charge it, however this isn’t recommended as it is an extremely inefficient (costly) way to charge the battery.
As I said earlier, I fully accept that my understanding may be flawed, so I would really appreciate those with more knowledge correcting any of the above because, if my understanding is correct, it is not possible for the car to perform exactly the same with a depleted battery as it does when the charged battery and petrol engines are both running in unison. Admittedly, if permanently driving in hybrid mode it is unlikely that the battery will ever fully deplete, but isn’t there a risk of it doing so for those who intend to use the all electric mode a lot and then join a motorway where they won’t get much benefit from regenerative braking?