Hybrid Electric Vehicles (HEV)

#1 Basic HEV Facts

A HEV is a Hybrid Electric Vehicle. ‘Hybrids’ have both a normal size fuel tank and a small battery.

The fuel tank provides the internal combustion engine with petrol or diesel. The engine consumes the fuel and makes the wheels go round.

The battery in the HEV powers an electric motor which can also make the wheels go round. However, as the battery is small, this type of electric vehicle can only run on electric power alone for a couple of miles and at low speeds.

HEVs can’t be plugged in, so they charge their batteries mainly by using up petrol/diesel in the internal combustion engine.

The battery also charges partly via regenerative braking – basically as you slow down, the kinetic energy is converted into extra battery energy, rather than lost to heat in the brake pads.

HEVs switch automatically between combustion and electric power, and the limited capacity battery helps to improve fuel economy and energy efficiency, while also reducing emissions around town when driving at low speeds.

Jargon alert! You will also read about series hybrids, parallel hybrids, and mild hybrids. The first two are simply versions of the HEV format, whereas the latter – also referred to as MHEVs – are not really electric cars at all. A mild hybrid, or MHEV cannot run just on the battery; its wheels are always dependent on the combustion engine.

#3 HEVs Cannot be Plugged in to Charge

There’s a lot of confusion about HEV charging, mainly due to the way they are often advertised as ‘self-charging hybrids’. Let’s clear away the fog.

Pure electric cars (BEVs) and plug-in hybrids (PHEVs) can indeed be charged by plugging into a charging point either at home, work, public charging station, etc.

A HEV, by contrast, has no charging socket and cannot be plugged in. How then does it charge its very small battery? How does it self-charge? It manages it in two ways:

1. By burning petrol or diesel inside its combustion engine to generate electricity to charge the battery, and/or
   
2. Via regenerative braking: a technique that all types of EV employ to convert the kinetic energy of the vehicle into battery energy when slowing down.
   

HEVs are also sometimes called full hybrids, especially by the UK government for some reason.

If you want more info on charging BEVs and PHEVs, check out our EV Charging Guide.

#5 HEVs – Environmental Impact Ranking

HEVs get a bronze medal when it comes to environmental impact.

BEVs secure gold – they are all-electric and zero-emission.

PHEVs get the silver medal – they have a medium-size battery and can be zero or very low emissions for up to 30 miles or so, but start polluting thereafter.

HEVs can only be filled with petrol or diesel, and so are very similar to any other type of internal combustion engine vehicle – they emit harmful gases and pollutants.

Their saving grace is that around town at low speeds they can run on battery power alone. Think of the Toyota Prius HEV taxi stopping and starting in a traffic jam. You won’t hear any engine noise until the driver speeds up or the battery runs out of charge.