Podcast ep. 07 – EV Metrics explained: units of measurement for electric vehicles (part 2)

Hello and welcome to the Electric Vehicle Experience

In today’s episode, we’re still talking about the units of measurement for electric vehicles.

If you didn’t catch the last episode, go get it to understand kW and kWh and what they mean.

Now let’s see how this applies to EVs.

kW measures the power that is being provided. We talk about power when you are charging your car. Let’s say that your car can take 150kW but it only gets 100kW because that’s the peak power of the charger you’re using.

If your battery is nearly fully depleted and you want to charge it fully, whether you’re using an 11kW charger, a 60kW charger, or a 350kW charger, you need to charge a certain amount of kWh to get it back to full.

The higher the kW rate you can get into your battery the faster you’ll get the needed kWh to get the battery fully charged. Or up to the charge limit you chose.

Imagine you’re serving water from a bottle into a cup. The amount of water that is coming out of the bottle is kW and the capacity of the glass is kWh.

Remember that kW is used both for the charging speed and for the discharging speed. The discharging speed is actually your energy efficiency. It’s the electric version of liters per 100 kms, kms per litre or miles per gallon.

The battery capacity kWh will be the electric version of the fuel tank’s capacity in liters or gallons.

When you’re driving at a constant 80 km/h you’re using a low kW number. And you spend kWh slowly, the stored energy will last for longer.

If you have a full bottle of water and you start dripping that water slowly, it will take longer to empty the bottle. In other words… your range will increase.

But if you press the right pedal all the way down you’ll drastically increase the kW in use and, as a consequence, the kWh will also be spent faster. In this case, your range will diminish.

It’s like inclining the water bottle a bit more to get the glass full quicker.

The units are different but the way they work is similar to those in a gasoline car.

In the beginning, I talked about the horsepower we used in gasoline cars. And I’ve talked about power a few times for electric cars.

1 hp = 0.745699872 kilowatts, I don’t know the precise number, it’s almost as long as a train. My previous car had 138 hp or 103 kW. It was normal to use HP to talk about a car’s power, both in conversations or the auto press but nowadays with EVs, it’s becoming more common to talk about kW.

And that adds a bit of confusion because it’s another unit that’s measured in kW.

One unit that we use a lot in EVs and on one cares in conventional cars is the refill or recharge rate. You never heard of anyone choosing a certain car because of how fast you could refuel it at the petrol pump, right?

In EVs that’s a thing. I think most people don’t need lightning-fast charging speeds but if you plan on using public charging during long trips with some regularity, avoid the cars that charge the slowest.

Last but not least, let’s talk about energy efficiency.

If you’re in Europe like me you most likely’ve been using liters per 100 kms. For electric cars, you would use wH per km or kWh/100 kms.

You can use any of them and it’s easy to understand both of them. For example, I’ve been getting an average efficiency of 149 wH per km. In kWh/100 kms it’s 14,9. Yes, that easy, no need for difficult conversions.

I’ll add a bonus.

Do you want to know how that relates to battery capacity?

If I have a 75 kWh battery and I spend 15 kWh / 100 kms…. you’re probably guessing it… if you divide 75 by 15 you get 5… so you can do it 5 times… because we’re talking about traveling 100 kms…. 5 times 100 kms…. we get 500 kms of range.

That means that if you average 15kWh/100 kms while driving a car with a 75kWh battery, you can drive it for 500 kms. If you’re brave enough, at least…

I know this episode was a bit dense in terms of information and I recommend that you go over it again if you don’t feel comfortable with these units yet.

When you do, it’s like riding a bicycle, it gets easy.

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Thank you for watching and I’ll talk to you soon