What is a self-charging hybrid electric car?

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The term ‘self-charging hybrid’ appears often in the advertising and marketing of certain models, but what does the term really mean and are they any different?

You’ve likely seen or heard the phrase ‘self-charging hybrid’, which has been used by Japanese brands Lexus and Toyota in advertising their electrified models, as well as by South Korean manufacturer Kia. It describes a type of hybrid car employing a petrol or diesel engine in combination with one or more electric motors and a small battery that never requires plugging in. This type of car is also known as a ‘full hybrid’.

The battery is topped up using a combination of energy from the combustion engine and energy recovered from the car’s brakes when it slows down. After a short spell of driving, the battery can transfer power to the electric motor, helping the car move along in traffic, when parking or if you hit the accelerator to gain speed, giving the engine a boost and saving fuel.

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Unlike a plug-in hybrid, a self-charging hybrid like this cannot be recharged from a domestic socket or a public charging point. Normally, they can only drive for a kay or two at most on pure-electric power, but usually the idea is that short periods of electric running throughout a journey can add up to significant fuel savings overall.

Self-charging hybrids shouldn’t be confused with mild hybrid cars. Those are fitted with a starter generator instead of a starter motor. They’re generally capable of idling without the engine on for longer in stop-start traffic, and in some cases can allow ‘coasting’ when cruising gently, where the car freewheels with the engine automatically switched off for brief periods. But they’re not capable of electric-only driving for any distance. A ‘self-charging’ hybrid would be slightly more fuel efficient than an equivalent mild hybrid.

How do self-charging hybrids work?

Self-charging hybrids usually have one or more electric motors, which are used to boost the performance or efficiency of a car’s petrol or diesel engine. Nearly all self-charging hybrid models use a petrol engine. Once the battery has charged up sufficiently, a self-charging hybrid can use this additional energy to help the car gain speed, reducing the burden on the internal-combustion engine. This saves fuel, therefore improving fuel economy during typical trips within towns and cities.

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Most self-charging hybrids are also capable of moving under electric power alone for short distances at lower speeds – most useful in slow-moving traffic and during manoeuvres like parallel parking. As well as conserving fuel, self-charging hybrids tend to have lower CO2 emissions than their purely petrol counterparts, making them somewhat better for the environment. Self-charging hybrids are so-named because you can’t charge the battery externally via a cable: all the energy is harvested from either the engine, the brakes, or merely the act of slowing down.

In some self-charging hybrids – the Toyota Yaris, for example – you can choose how aggressively the car will decelerate the moment you take your foot off the accelerator. The more severe the setting, the more energy you’ll recover to store in the battery. In some cases, this will allow you to drive without using the brake pedal at all – although you’ll still need to use it if you need to slow down suddenly or perform an emergency stop.

What are the benefits of a self-charging hybrid?

If you frequently drive in built-up areas, self-charging hybrid technology reduces the workload on a petrol or diesel engine, reducing your running costs and air pollution.

Self-charging hybrids also cost less to buy than plug-in hybrids because their smaller battery packs are cheaper to produce. Many owners of full hybrid models also report lower maintenance costs, because the braking effect of the electric motor reduces wear on the brakes and tyres, helping them to last longer. Hybrid models like the Toyota Prius have proved to be very reliable, with fewer items like a clutch that need to be replaced.

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What are the cons of self-charging hybrids?

While a self-charging hybrid is likely to be a better prospect for some drivers than a plug-in hybrid, it’s important to remember that their efficiency benefits are much reduced at motorway speeds. On fast roads, you’re mostly reliant on the internal-combustion engine; if you travel cross-country a lot, then pure petrol, diesel or longer-range electric cars will probably be more suitable.

Because of their small batteries, self-charging hybrids can’t travel far on electric power alone; usually no more than a mile or two. So if you frequently drive short distances and you can charge at home or at work, a plug-in hybrid might be more cost-effective. Not only will you save money by using electric power rather than petrol or diesel, you’ll still have the option of driving further using conventional fuel should the need arise.

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It’s also worth noting that while there are a few all-wheel-drive SUVs available with the technology on board, these can’t match their diesel equivalents for pulling power, so it’s worth considering this if you’re a caravan or trailer user.

Finally, self-charging hybrids are unlikely to suit driving enthusiasts. Most of them are designed to save fuel and make driving relaxing and pleasant, as opposed to exciting or involving. However, there are some fast hybrids out there if you really want the best of both worlds.

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