Our Fleet Product and Policy Manager, Mike Coulton explains the three key components of an EV: a battery to store energy (electricity), a motor (one or more) to drive the wheels, and an onboard charger to charge the battery.
The charger itself is really key, and most people don’t understand that it is actually inside the vehicle – the plug on the wall merely delivers electricity to the charger. Domestic and many commercial power supplies will be Alternating Current (AC), either in single-phase (up to 7kW) or three-phase (up to 22kW). However, lithium-ion batteries (a battery used in an EV, laptop, smartphone etc.) store electricity as Direct Current (DC), so the onboard charger converts this AC power supply into DC energy.
The exception to this is ‘Rapid’ and ‘Ultra-rapid’ charging (>50kW and up to 350kW currently), which is DC straight to the battery and is much, much faster. However, the infrastructure is also much more expensive, and regular/consistent rapid charging is not considered a ‘best practice’ for battery life.
One important point to note: often, the onboard AC charger can be the limiting factor in charging, which is an important fact when considering workplace charging infrastructure: just because you can install three-phase AC chargers delivering 22kW doesn’t mean your fleet of vehicles can accept that much power; for example, a Volkswagen ID.3 (and most other EVs) can accept a maximum of 11kW AC, so there’s currently no benefit installing 22kW chargers for a fleet of those.
This brings us on to the battery; EVs use lithium-ion batteries because they have a high energy density and can store a lot of power for their size. They are also stable (safe!) and can cope with regular charging/discharging. Battery capacity (size) is measured in kWh (kilowatt-hours), which is “a measurement of electricity that is equivalent to the amount of energy expended in one hour by one kilowatt of power” – or to put it simply, how much energy the battery can hold.
So to use an analogy of filling up a bucket of water, the size of the bucket represents the battery size (measured in kWh), and the speed at which you can fill it up is the diameter of your hosepipe that controls how much energy can flow into it in a given time (measured in kW). The battery is effectively the fuel tank in your EV.
Thirdly, the motor (or motors) takes the battery’s energy and converts it into motion by driving the wheels, replacing the petrol or diesel engine in your Internal Combustion Engine (ICE) vehicle. EV’s can have one, two, three or even four motors – and there are advantages and disadvantages to each setup. Entry-level models will often have one motor driving either the front (e-golf) or rear (ID.3) wheels to keep costs down.
Longer range and performance models will often have two or more motors; these provide four-wheel-drive traction for faster acceleration, hence how a Porsche Taycan Turbo S can get from 0-60mph in 2.8s! However, they can also shut down the largest of the motors when cruising at steady speeds and use only the smaller, more efficient motor to improve efficiency and increase driving range. Ultra-high performance EV’s may have three (e.g. Tesla Model S Plaid) or even four (e.g. Rimac Nevera) motors, one for each wheel, which can be used for fancy stuff like torque vectoring…but that’s another story for another day.
A final thought on ‘Why EV? Not only are EV’s ‘zero emission’, but they are also extremely efficient compared to petrol/diesel and hydrogen fuel cell vehicles (FCEV), particularly if they can be powered directly from a renewable source, such as solar panels.
To bring that to life: an electric motor is around 90-95% efficient, so, even taking into account grid-generated electricity, the overall energy efficiency of an EV is approximately 70-75%. Compare this to an ICE vehicle that is typically only around 20-30% efficient, and you’ll find up to 70% of the energy is lost through friction in the engine, gearbox and drivetrain to heat and noise. Even FCEVs are only circa 40% efficient, so whilst they are also zero-emission vehicles, they are a lot less efficient. Considering all this, you can start to see the many other advantages of moving to an EV over and above the obvious tax savings and running costs.
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