The brave new world of electric cars brings with it a whole new lingo. Forget your miles per gallon, let Vanarama teach you why it’s all about kilowatt-hours now…
Perhaps the most common ‘technical’ term you will come across when people are discussing electric cars is the kilowatt.
Watts are simply a unit of power and show how much power can be produced by the machine you are using. It’s why your 100-watt light bulb glows brighter than a 60-watt…
But understanding exactly what a watt means (sorry…) and why it’s important in helping select your car is a good leaping off point.
A kilowatt is simply 1000 watts (like a kilogram is 1000 grams) and you’re most likely to see it used on its own as a unit to show how much power your electric car’s motor can produce.
It’s the closest you will get to a ‘horsepower’ figure for your EV. One kilowatt is about 1.34 horsepower, so a 100kW EV motor produces about 134 horsepower in ‘old’ units. The higher the kW rating of your motor the more ‘performance’ power you will get but the faster you will be able to drain the battery too…
But being physics, it’s never quite as simple as that. Because those smart scientists have also stuck a little ‘h’ on to the end of our kilowatt to create something called the kilowatt-hour.
You’ll see the kWh crop up a lot, too, when you’re researching your ideal EV. It’s used to explain not the performance of the motor (that’s kilowatts all on their own, remember?) but the total capacity of the battery that feeds that electricity to the motor.
Again, in simple terms, the kWh shows how much energy can be provided at a given rate over a given period (in this case an hour…) and the easiest way to get your head round it is to simply think of kWh as the equivalent of litres in your fuel tank.
Take 2 cars with the same power motor. One has a 35kWh battery pack and the other a 70kWh battery. Drive them at the same speed, in the same conditions, over the same distance and you will get pretty much twice as much range out of the 70kWh car as you will its little friend.
It’s not an exact science because factors like the extra weight of a larger battery will impact on your overall range but as a simple rule of thumb the more kWh you’ve got underneath you, the more range you will get…
It’s worth noting, too, that if you’re in the market for a more performance-oriented EV – and the acceleration from an EV sportscar is truly something to behold – then you’re going to want to make sure that the model you choose has enough battery capacity to allow you to enjoy all that performance.
It’s why you’ll find cars like the Tesla Model S boast battery packs as large as 100kWh – you need a lot of electricity to generate 615kW of power from their motors!
Knowing the kWh rating of your battery allows you to play another trick, too. Because all chargers that you use to top up your batteries will be rated in plain kilowatts (kW), then you’ll instantly know how many hours it will take to deliver the energy you need.
A 7kW charger attached to a 70kWh battery? That’s a 10-hour charge time to go from 0 to 100%. At least on paper…
Battery chemistry means that once you’re past 80% charge it gets harder to cram in the electrons at the same rate – particularly if you’re rapid charging – so your charging time can slow over the last 20%. But as a rule of thumb, knowing how many kilowatts you can load in an hour helps you plan your charging routine, whatever type of charger you’re using.
It’s one of the reasons that car makers will often quote you charging times between say 20 and 80%. It’s also the reason you will see people opting to disconnect from public chargers when they reach 80%, when the law of diminishing returns means that it’s quicker and cheaper to head off.