Correct me if I’m wrong…(corrected) I got it wrong the first time

So which car is more environmentally friendly and how do you calculate the CO2 output of an E.V. versus a Petrol car

Here in NZ we are blessed with 4/5ths of our power coming from renewables. LL though this has shrunk of late

The balance comes from fossil fuels and is required to maintain the consumption during the year in the North island. The reality is the renewable energy supply cant keep up with demand and anywhere from 40% down to 15% of the more populous island requires burning fossil fuels to provide us power. Any increase in power over what the clean generation can cope with increases the demand on predominantly coal and gas.

Remember that last sentence as we continue on this train of thought.

CO2 is the apparent villain of burning fossil fuels. We are told to reduce our carbon footprint to save the planet and our leaders have said they will make our government cars all EV’s by 2025, or 2030, or at some stage.

but while your local Greenies are out saving the world one E.V. at a time i decided to sharpen my pencil and do some math.

First of all lets take the energy consumption of the average motorist and compare the damage to the environment solely from the energy consumption and ignore the dirty batteries etc that help make E.V’s go.

So let us say the average motorist drives 200 k/m per week which is 10,400 k/m for the year.

for petrol cars (depending on what you drive) you will consume 4 to 12 liters per 100km the higher amount is for your gas guzzler and the lower amount for the efficient car. lets go half way along at 8 litres per 100 k/m

We can see that the 8 liter per 100km car creates 25,300 grams of CO2 by the time it competes this distance. If we extrapolate this out over the year we end up with 10,400 k/m by 253 grams of Co2 or 2,631 kilos of CO2.

Plant 93 trees and technically this will give you a zero footprint.

Now lets look at the E.V. Depending on if you have a more economic EV like a Nissan Leaf or a power guzzling Tesla Model x you will consume between 15kw/h to 25kw/h per 100 k/m. from your pockets point of view you are winning but how does this look when you compare this to the power grid?

If you are in the South island you are winning from an enviromental point of view. hydro is powering your E.V. so you can carry on telling everyone you are saving the planet. Just don’t mention the cobalt mining and child labour and you will be fine.

However if you are a North Island E.V. driver then depending on how you try and spin the story you are of course using more. If we are nice and say that 80% of your power is renewable (oh but it is) but lets be nice and play the game. 20% of the power you consume is generated from fossil fuel. extrapolating out the midway point of 20kw/hour per 100 k over the 10,400 k/m for the year gives us 2.08 gigawatt/h energy consumption for the year. about half will come from coal and half from gas of this 20% which if we look at the graph below gives us ((2.08x1001x0.5) +(2.08X469X0.5)/5

SO this gives you a total of 208 kilos of Co2 from the coal and 98 kilos from the gas or a total of 306 kilos of CO2 your driving is putting into the air. Well done you are way cleaner at only 306 kilo’s of CO2.

But hang on, what did we learn at the beginning? That’s right any new load just adds 100% to the fossil fuel because all of the renewable are being used on existing load. this means your lovely little E.V. is spewing out 1,530 kilos or 1 and a half ton’s of Co2 compared to the 2,631 from the petrol car.

So the EV wins again on looking only at the CO2 emissions of powering it.

What you also need to look at is the difference in manufacturing an E.V. to a petrol car and the long term environmental impact of the two when their parts and ultimately the entire car is laid to rest. Batteries being the biggest one

Feel free to sharpen your pencil and prove my calculations wrong.

I have said it once I will say it again. technology will guide through to better environmental outcomes.

Power generation, large capacity battery storage and better materials for making batteries will undoubtedly make the EV to car of the future. But as for today its not the shining beacon of environmentally friendly just yet.

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2 Comments
carlplanetb December 20, 2020
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Thanks for the feedback it looks like a bit of a miscalculation on my part - only 100x out eh mmmm. Ironically it is the production of CO2 that is claimed to be warming the planet is what I actually don't agree on but it certainly has put rest to my argument there. Thanks I will need to update the post
Samuel December 20, 2020
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I think you're out by a factor of 100 as you misread the first graph. The first graph shows emissions as gCO2e per kilometre. You have misread this as being per 100km, and adjusted it down to 2.53 g/km. It should be 253g/km. Think about it for a minute - if you burn 8L of fuel while driving 100km, or maybe 6kg of fuel, much of which is carbon, once combined with oxygen this is going to produce well over 6kg of CO2. So the 253g value cannot be g/100km, it's impossible. So this means the petrol car is producing 2800 kg per year (your 28kg value x 100), while the electric is producing 1500 kg. However, as you will know, this is obviously too simplistic. That's not accounting for transmission losses, which will push up the electric car's emissions further - though possibly still lower than the petrol car. At the end of the day, it is the emissions associated with the battery technology that actually tip electric cars over the line to being worse than petrol cars, if you ignore that you simply don't have the full picture and will think electric is better. So I'm not disputing your conclusion, I'm just correcting your maths in how you got there.