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Difference between a mild and plug-in hybrid

As the rest of the world continues to make the transition to new-energy transport, many people in South Africa are still skeptical about the viability of electric vehicles (EVs) in a country where cars are expensive and where the lights in our homes can’t stay on for the full duration of a single evening.

This is where hybrid vehicles come into the picture, as they theoretically offer the best of both worlds with the environmental considerations and fuel-savings of EVs while still offering the reliability and practicality of a typical gas-guzzler.

However, it’s important to understand that not all hybrids are the same, as there are in fact several different forms that the world of semi-electric vehicles can assume.

The two most common types of hybrids you will likely hear about are mild hybrids and plug-in hybrids which, in practice, operate the same, but use very different methods to do so.

Mild hybrids

If you are looking for an affordable hybrid vehicle in South Africa, it will most likely be using a “mild” setup.

This is because a mild hybrid, in function, works almost identically to an internal combustion engine (ICE) car, because it is still a petrol drivetrain that is doing most of the work.

On the most basic hybrid models, automakers replace the traditional starter motor and alternator with a small electric generator and battery which typically runs at a higher voltage of between 12V to 48V.

This electric power source is far too small to drive the car by itself. Instead, it offers assistance to the fuel-driven engine which in turn allows the car as a whole to run more efficiently, hence the “mild” designation.

The improved electrical system also means other functions of the auto, such as the stop-start system and user features like the infotainment and air conditioning, function better and don’t require the petrol engine to top up the battery as you’d find with a traditional alternator.

Since a mild battery is so small, it doesn’t need to be plugged into a wall socket to be charged but is charged by the ICE and a few other methods, such as regenerative brakes, which are able to convert the kinetic energy generated during braking into electrical energy which can be fed back into the battery.

Certain automakers offer another form of hybrid known as a parallel setup, which have one or more bigger electric motors mounted directly onto the wheels or driveshaft, and is actually capable of driving the car at low speeds before the combustion engine takes over again.

These hybrids are still not capable of driving real-world distances on pure electric power, but the advantage of this system can be seen in something like heavy traffic where the electric motor can allow the vehicle to crawl in bumper-to-bumper road conditions without the need for the ICE to be inefficiently burning fuel at low revs.

Plug-in hybrids

A plug-in hybrid, or PHEV, is arguably the best definition of a semi-electric vehicle, as they feature both a petrol engine as well as a substantially more powerful battery and electric system which is capable of driving the car by itself for dozens of kilometres.

The majority of plug-ins currently on the road are not able to go further than 100km on just the electric motor, hence they still have the need for a combustion engine, but this range is suitable for most people’s everyday activities such as driving to work, the shops, or taking the kids to school.

This means it is technically possible to treat a PHEV as a fully-electric car, depending on your daily requirements, with the ability to fall back on a petrol powerplant for those longer trips or when the battery is depleted.

This is where the term “plug-in” becomes relevant, as a PHEV has two different filler caps, one for inserting fuel from the pump, and another to plug the car into a charging socket.

The petrol engine is able to charge the battery to a certain degree as well, and PHEVs are still able to make use of other energy-saving tricks like regenerative braking, but the much higher capacity of a plug-in unit means it will still be necessary to charge it from an external power source from time to time.

The obvious drawback of a plug-in hybrid is its upfront cost, as you are effectively paying for two powertrains at once, and as such in South Africa most PHEVs can currently only be found with higher-end brands such as Lexus and Range Rover.

It bears mentioning, however, that while mild hybrids are more “affordable” when compared to plug-ins, they still aren’t cheap, as even something like the Toyota Corolla Cross hybrid has a minimum window sticker of R442,400.

Another thing to consider is that all hybrids will need to have their batteries replaced at some point – usually within 10 years – which can be a significant cost, and hybrid technology is also progressing at a rapid rate meaning models may become outdated more quickly than other forms of transport.



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