How do self-charging cars work?

Toyota, Lexus and Kia use self-charging as a term to describe their mild hybrids.

Mild hybrid doesn’t sound as exciting or technologically advanced as a self-charging car, which is probably why their marketing departments opted for the more mysterious and intelligent-sounding self-charging terminology.

How Do Self-Charging Cars Work?

A self-charging hybrid has a small battery and an electric motor. When the vehicle brakes, the initial phase of braking is used to charge the battery. Brakes (disks and pads) then kick-in after.

This is a basic form of regenerative braking (or regen) something plug-in hybrids (PHEVs) and electric vehicles (BEVs) do too, but to a greater degree and effectiveness.

The small amount of energy recovered from braking is then able to be used to drive a limited distance.

What Powers a Self-Charging Hybrid?

Exhaust pipe emissions on a self-charging car

Unfortunately, a self-powered car breaks the laws of physics, as the energy must come from somewhere. In one of Kia/Lexus/Toyota’s mild hybrids, the power comes from burning fossil fuels – the petrol in the internal combustion engine.

This means self-charging cars are 100% powered by petrol. All the propulsion achieved is down to petrol – since the cars don’t plug-in.

If we refer to mild hybrids as self-charging, we should really refer to all petrol and diesel cars as self-charging, since these cars don’t need plugging in to charge their 12-volt battery which powers the wipers, headlights and other electrical ancillery services.

How Far Can A Self-Charging Car Travel?

Toyota et al claim that their mild hybrids can be driven over 50% of the time on “pure electricity”. That makes them seem awfully green, given we tend to associate electricity with being green and petrol with being polluting. This claim is misleading for two reasons:

  1. It’s crucial to remember that Totota reference time not distance – if you drive in stop-start traffic, the engine might be off for a large proportion of the time as you’re stationary. Some of the slower speed driving may be achievable using the battery, but because the battery is very small, it will drain extremly quickly and require recharging – so the petrol engine turns on. In terms of distance driven, I’d estimate only around 5-10% of miles/kilometers are driven using the battery.
  2. All the electricity used to driver is generated by burning petrol, so it’s certainly not the clean energy you can get from the grid or solar on the roof of your house for example.

Do Self-Charging Cars Exist?

Will we ever see a car that can power itself? In the Toyota sense of self-charging, no. It’s not possible to drive a mild hybrid without putting petrol in it.

Lightyear One

However, there are projects like Lightyear One, working to create cars that you may never need to plug-in! These are pure electric cars (not hybrids, so no fossil fuels) and can be charged by plugging-in, or from the solar panels built into the roof, bonnet and boot! ☀️⚡🔋🚗

Lightyear are aiming to be able to charge an impressive 12 kilometres (7 miles) from 1 hour of sunshine charging – using the solar panels on the roof! For those who drive short distances, or only travel infrequently, that could mean you’d never need to plug-in!

More info on the Lightyear One in this Fully Charged video.

Should Self-Charging Be Banned?

In Norway (home of the EV, where over half of cars sold in 2020 were fully electric) they’ve banned adverts that reference “self-charging” believing the term is misleading.

I believe marketing a petrol car (100% powered by fossil fuels) as self-charging should be banned, as it’s extremely misleading. It makes polluting cars that burn fossil fuels seem cleaner and if you don’t do your research, you might think you’re doing your bit to look after the environment when actually, nothing could be further from the truth.

Electric car cost per mile

Last time I looked at the difference in energy usage between petrol and electric cars. Another way of comparing EVs, hybrids and ICE cars is cost per mile. Using the Mini Cooper, we can compare all three. This example is based on UK units, assuming petrol is costs £1.30 per litre and electricity 14p/kWh – i.e charging at home.

Petrol

The petrol Mini Cooper S has a 44 litre fuel tank, and an average consumption of 44 miles per gallon – UK/Canadian mpg. A full tank of fuel can take the car 425 miles at a cost of £57.20, meaning each mile of driving costs 13.5 pence.

Hybrid

The Mini Countryman Cooper S plug-in hybrid has a 36 litre fuel tank and a 7.6kWh battery. Combined mpg figures range from 50.8mpg to 56.6mpg so we’ll use 53.4mpg for the comparison.

That means with a full tank and a full battery, you can travel around 423 miles – similar to the petrol car. The cost of 36 litres of petrol is £46.80 and 7.6kWh of electricity costs £1.06, making the total cost per mile around 11.3 pence.

Electric

The Mini Cooper Electric

The Mini Electric has a 32.6kWh battery and a range of 115 miles. It costs £4.56 to “fill up” the battery meaning each mile costs 4.0 pence.

Hybrid Inefficiencies

Interestingly, the hybrid is less efficient than the electric car when running on battery power and less efficient than the petrol car when running on the petrol engine. This is because it’s not just carrying an engine and a fuel tank, or a motor and a battery pack, it’s carrying all four all the time!

Hybrids were a great tool in the transition from ICE to EV, proving the concept and raising awareness. I believe they are no longer relevant however, as they’re significantly less efficient than their EV counterparts and don’t offer the electric range that people really need. The addition financial and efficiency costs don’t make hybrids worthwhile.

Most Efficient Car Pence Per Mile

The Hyundai Ioniq Electric

We’ve already established electric cars are far more efficient than petrol and hybrid-powered cars, so what’s the best of the best, the most efficient electric car? That title is shared by the Hyundai Ioniq Electric and the Tesla Model 3 Standard Range Plus which use just 240 watt-hours of juice per mile.

The Ioniq can drive an impressive 160 miles on a 38.3 kWh battery pack. It costs £5.36 to charge empty to full, at a cost per mile of 3.4 pence.

Just 3.4 pence for every mile of travel! That’s a quarter of the cost of the petrol Mini Cooper S!

The Model 3 can drive 195 miles (140 in winter, 275 in summer) on its 50 kWh battery pack. 50 kWh costs £7.00 on a £0.14/kWh home supply, which gives it a cost per mile of 3.6 pence. Worst case that’s 5.0 pence per mile in winter, best case it’s as low as 2.5 pence per mile in summer.

EV Tariffs

Some electricity providers now offer electric car tariffs, which make it even cheaper to charge. Some even pay you to take power off the grid when demand is low but supply is high!

£0.05/kWh is not uncommon. Charging a Model 3 at that price could give you 275 miles of range for £2.50.

0.9 pence per mile.

Petrol cars simply can’t compete with electric cars on pence per mile. EVs are too efficient 🙂

How many miles per gallon do electric cars get?

Electric cars aren’t powered by diesel or petrol, so they don’t have an official miles per gallon figure. That said, there are ways of working out how efficient they are and even give them a rough miles per gallon.

How Many Kilowatt Hours is in a Gallon of Petrol? ⛽

The US governments fueleconomy.gov website calculates 1 (US) gallon of gasoline is equivalent to 33.7 kilowatt hours of energy – or kWh.

A US gallon is 3.785 litres, whereas in Canada and the UK a gallon is 4.546 litres. This means a (UK/Canadian) gallon of petrol is equivalent to 40.5 kWh of electricity.

Each litre of petrol is equivalent to 8.9 kWh.

Toyota Prius vs Nissan Leaf MPG

The Toyota Prius was once regarded as the sustainable choice for environmentally conscious drivers, but in recent times its crown has slipped a little. This might be partly because of Toyota’s inaccurate branding, claiming that it sells “self-charging cars”, when in reality a (very small) battery is charged by recovering motion which was achieved by burning petrol or diesel. That’s how most cars charge their 12-volt battery, it’s not self-charging! 😂 It’s also because electric cars are now more viable and mainstream.

The Nissan Leaf is currently the top-selling electric vehicle of all time (at least until the Model 3’s first quarter sales are released) so let’s use that for the comparison. An “efficient” hybrid vs an electric vehicle, how do they compare?

The Nissan Leaf

The Totoya Prius achieves 62.4mpg (UK/Canada) using 4.5 litres to travel 100 miles. The Nissan Leaf by comparison achieves the equivalent of 129.7mpg (UK/Canada) taking just 2.2 litres to travel 100 miles.

This highlights the efficiency of electric vehicles.

The Leaf uses less than half the energy of the Prius (the previous “gold standard”) to travel the same distance.

Efficiency

Internal combustion engine (ICE) powered cars convert around 12-30% of the petrol or diesel they consume into forward motion powering the wheels. This is because an ICE car loses over two-thirds of its energy through heat 🔥 and the transmission of power through the drivetrain.

Even the most inefficient electric vehicles translate at least 60% of the electricity stored in the battery into forward motion. If driven using regenerative braking (to re-capture energy, rather than scrubbing it off via breaking) EVs can be around 90% efficient!

How Big is an Electric Car’s Fuel Tank?

Electric car battery and powertrain

Here’s another interesting question, if an electric car had a fuel tank, how big would it be?

The Tesla Model 3 Standard Range Plus has a 50kWh battery, so if one US gallon of gasoline/petrol is equivalent to 33.7kWh, then the Tesla Model 3s equivalent petrol fuel tank would be 1.48 US gallons – or 5.62 litres.

That’s right, an electric car can achieve a range of 200 miles (275 if driven carefully in warm weather) on less than the equivalent of 6 litres of petrol!

You can also compare cars on a cost per mile basis, which is what I’m going to write about next, with the help of the new electric Mini!