When it comes to hybrid vehicles, there’s pretty much a straight choice between a HEV and PHEV. But what do these two terms mean, and what are the benefits and drawbacks of each? Here’s our handy guide to hybrids.
HEV
This term stands for Hybrid Electric Vehicle and there are actually three main types – parallel, series-parallel and series hybrid vehicles. The waters have been muddied further by the advent of cars that are often termed ‘mild hybrids’, the most obvious examples of these being the latest big Audis, in which the hybrid system is only used for torque infill during acceleration, coasting the car ‘engineless’ at high speeds and also enabling auto-stop-start technology sooner in traffic; Suzuki uses a similar, less-powerful system on some of its vehicles, called Smart Hybrid Vehicle System (SHVS).
Parallel, mild-parallel and series-parallel hybrids, though, essentially perform the same function. They unite an electric motor with either nickel-metal hydride or more advanced lithium-ion batteries, as well as some form of combustion engine (the majority of HEVs use petrol engines, but there are some diesel-electrics available), in order to improve the fuel economy and reduce the CO2 emissions of the vehicle in question. There is no facility to plug any form of electric power supply into the car anywhere, with all charging of its onboard battery systems handled by the combustion engine, as well as kinetic energy harvested from coasting and/or braking. You’ll therefore not often be driving on electric power alone, but these vehicles can creep around without using their petrol or diesel engines at very low speeds, while they also can switch off the engine to coast while driving at higher pace. Toyota and Lexus are the masters of HEVs, having a wide variety of models with the conglomerate’s ‘Synergy Drive’ system – the most famous model being the Prius, but you’ll find any Toyota with ‘Hybrid’ on its rear and any Lexus with ‘h’ in its badge are using this technology. Honda also has a history of HEVs, chiefly the two versions of Insight, the CR-Z sports coupe and an older version of the Civic hatchback (not to mention the new-for-2019 CR-V Hybrid), but there are more brands that employ HEV technology in their cars.
Series hybrids confuse the issue somewhat, as these are primarily electric vehicles that only use an onboard combustion engine for the purposes of charging the battery pack. They do have a plug-in facility for charging the battery, but rather than being called PHEVs (see below), they’re referred to as ‘range-extended’ electric cars. Examples of these are rare, but the Opel Ampera was one of the few well-received series hybrids (not sold officially in Ireland), while the (now-defunct) BMW i3 Range Extender was also a series hybrid. It used a small BMW motorcycle engine in the rear to extend the car’s electric range, but the crucial thing to understand – with both the Ampera and the i3 REx – is that their onboard combustion engines never power the driven wheels directly; the electric motor is always in charge. However, the inclusion of any form of combustion engine at all, even if small (in the case of the i3) means they cannot be called Battery Electric Vehicles (BEVs).
PHEV
Plug-in Hybrid Electric Vehicles are an evolution of parallel, mild-parallel and series-parallel hybrids, in that they have larger battery packs and more potent electric motors, which allow them to drive for extended periods on electric power alone. The benefit here is that you have all the zero-emissions driving benefits of a full BEV, only without any range anxiety because – should you run out of battery power on the move – then the vehicle will switch to its combustion engine and continue driving just like a conventional car. There are lots and lots of examples of PHEVs, including a PHEV version of the Toyota Prius, as well as any BMW sold under the ‘iPerformance’ brand (all models with an ‘e’ at the end of their model designation, e.g. X5 xDrive40e) and the i8 sports car, the Mitsubishi Outlander PHEV, any Mercedes with a lower-case ‘e’ badge, many Volvos (usually badged T8 Twin Engine, but also Plug-in Hybrid on older models too), Volkswagens with ‘GTE’ badges (the Golf and Passat, in the main) and Porsches sold as ‘E-Hybrid’ models. Confusing the HEV/PHEV/BEV issue is the Hyundai Ioniq, which is a model built by the Korean company as a bespoke electrified car – and it’s sold in all three guises, as the Hybrid, the Plug-in Hybrid and the Electric. The Kia Niro is also available as a HEV or PHEV.
The pros and cons of HEVs and PHEVs
HEVs (not including ‘range extender’ series hybrids) are typically easier to use than PHEVs, as they drive entirely like conventional combustion-engine-only cars and have no need of plug-in charging sessions, while they’re also cheaper to buy – they’re technologically simpler, meaning there’s less development costs inbuilt into each vehicle. They also maximise the practicality of their given body shape, because their small electric motors and battery packs do not take up a lot of space in the structure of the vehicle. However, they cannot run for any great length of time on electric power alone, meaning you’ll still be fuelling them at petrol stations – just like any car without electrification. They also don’t have super-low CO2 emissions, which means they’re not eligible for as many tax breaks as a PHEV is.
PHEVs offer a ‘best of both worlds’ scenario for buyers who want to adopt the electric-car lifestyle, but who are a little worried about whether a full BEV will suit their needs. They have the ability to drive for considerable distance without any recourse to their combustion engine at all, and as a result of NEDC/WLTP emissions testing, they have extremely high quoted average fuel economy and low official CO2 outputs, making them eligible for greater tax breaks. For new cars, PHEVs qualify for SEAI grants of between €2,000 and €5,000, whereas HEVs do not. Nevertheless, the associated electric running gear takes up more space in these vehicles and can often reduce their boot capacities or seating room, when compared to an equivalent model with a conventional drivetrain, and to get the best from them, you absolutely must charge PHEVs on a regular basis – otherwise, they’re standard petrol and diesel engines that are hauling around a lot of extra weight (in the form of the electrical systems) for no good reason, meaning their fuel economy will be a lot lower than quoted.
Which is best for me?
We’ve touched on it above, but a PHEV suits a particular type of user. If you’re an urban or semi-urban dweller, who has a regular commute of less than around 30km (each way) and who works at a company where they have plug-in charging bays in the car park – and you religiously charge the vehicle, both overnight at home and then when you’re at work – then you cannot beat it; especially if, on occasion, you need to travel longer distances (to see relatives or to go on holiday, for example), when its combustion engine will make it more worthwhile than a full BEV. Used like this, it’s entirely possible to drive a PHEV and only put fossil fuel in it two or three times a year. That’s incredible, especially when some PHEVs are very large and luxurious SUVs.
However, PHEVs are expensive, even second-hand, and they’re not as efficient when they’re running on their combustion engines. For most people just looking to save a little fuel, without going too far down the electric car route, then a HEV fits the bill perfectly. They’re more likely to attain economy figures that are closer to their manufacturers’ claims and they’re less expensive to buy, as well as less compromised in the packaging department, which makes them an ideal ‘starter EV’ choice for someone migrating from a diesel C-segment hatchback.
Carzone - 23-Nov-2018