- Carwow tested the efficiency of a BMW 520i, 530e and i5 with interesting results.
- The 520i proved more efficient than a 530e with an empty battery.
- Plug-in hybrids should only be bought by people who know they can commit to charging them regularly.
Plug-in hybrids promise to offer the advantages of both combustion cars and electric vehicles combined into one. They have dozens of miles of electric range, as well as the versatility of starting up their combustion engines for added range and performance. They have ridiculously low claimed fuel economy numbers, but you can only come close to matching them if you never allow their batteries to go flat.
When a PHEV’s battery state of charge drops below the point where it can propel the car purely electrically, the gas engine takes full propulsion duty.
However, in this situation, it not only has to propel the car, but it also has to power a generator to put juice back in the battery, which means it will use more fuel than if it only had to move the car.
That’s why there’s a significant difference between the efficiency numbers of PHEVs running with and without juice in their batteries. Running a PHEV with its battery empty all the time will result in it using more fuel than if the vehicle had just the combustion engine without the electrification.
This was proven in a recent Carwow video, which pits three versions of the BMW 5 Series against one another in a range and efficiency challenge. They compared a 520i, a 530e and an i5 on a set route, measuring various parameters and seeing how close they all came to matching their manufacturer-claimed numbers.
There’s a bit of weirdness and inconsistency in how the video is structured, but by the end of the route, the 520i proved more efficient than the 530e. Both have the same four-cylinder turbo engine, but in the 530e, it is aided by an electric motor squeezed into the gearbox, which draws electricity from a 19.7-kilowatt-hour battery pack.
Now, sure, it does provide over 60 miles of pure electric driving (which it almost matched in real-world driving in the video), but it’s also considerably heavier than the 520i, which was just a mild hybrid.
The 530e’s extra heft makes it less enjoyable to drive, since weight is supposed to be the enemy of all things holy to a driving enthusiast. Interestingly, when they tested the braking performance of all three 5 Series variants, it was the PHEV that stopped in the shortest distance.
Its superior braking performance may have come courtesy of its ability to blend both regenerative braking from its electric motor and the power of the friction brakes. The i5 can do the same, but it has even more mass to bring to a halt. Even so, the fully electric i5, which we've tested in several versions, including the M60 Touring, would be the one we would pick out of the three.
We’ve been saying for years that while PHEVs sound excellent on paper, some claiming upward of 235 mpg, if you don’t commit to charging them regularly (daily, if you have a big commute), they may not be worth buying. For most drivers, a normal non-plug-in hybrid is a much safer bet since it brings actual fuel efficiency improvements over a comparable non-hybrid gas car without the driver having to make any adjustments.
Going for a full EV also makes sense since EVs have much bigger batteries and don’t need to be plugged in as frequently as PHEVs do, and they charge faster too.
