In short, the answer is “Yes”, but that would make a very short blog post, so I’ll show my working.
Let’s look at the relative carbon emissions of an electric car compared to a traditional fossil fuel powered car. The question is, what is the most carbon efficient way to travel your next mile by car? Let’s assume for now that you need a car, but we’ll come back to that later.
There are two main factors that we need to take into account: the carbon emissions that result from the fuel that the car uses, be it petrol, diesel or electricity, and the embodied carbon of the car itself.
The embodied carbon of an object is all the emissions that result from its production. A lot of energy goes into the mining and refining of raw materials, and then more energy is used to turn those raw materials into the finished product. Unfortunately, despite the huge increase in renewable energy generation across the world over the last few decades, most of the energy used to produce a new car will have come from burning fossil fuels.
As you can imagine, the embodied carbon of a new car is a hugely complex thing to work out. Luckily, smarter people than I have already given it a go. This report estimates the embodied carbon of a small petrol or diesel car to be about 8.5 tonnes of CO2e. This is roughly the same as the annual carbon footprint of the average UK person. So, it’s a lot! Interestingly a small electric car actually has a larger embodied carbon, about 14 tonnes CO2e. The difference is almost entirely due to the batteries, which are currently quite carbon intensive to manufacture.
The size of the car has a huge impact on its embodied carbon. The difference between a Citroën C1 and a Range Rover Sport could be as much as a factor of FIVE!
So here’s my first environmental car buying top tip: whether it’s petrol or electric, buy the smallest car you can!
So, this is a bad start for the electric car. Buying one is likely to result in the release of 5.5 tonnes more CO2 into the atmosphere than buying a petrol car. But of course, that’s only one piece of the puzzle. Electric cars result in significantly lower carbon emissions when they’re run than a petrol car. That’s true even today, when most of the UKs electricity is generated from gas, and still some coal. Let’s look at the numbers.
Burning a liter of petrol results in the emission of approximately 2.31Kg of CO2. How far that gets you depends on how efficient your car is, but let’s assume you can get an average of 50MPG, with a mix of town and motorway driving. That means a petrol car will emit 210g of CO2 per mile.
What about the electric car? To work that out we need to know how much carbon is released when we make electricity. This varies significantly from hour to hour, and from day to day. When the sun shines and the wind blows renewable generation picks up, and coal and gas power stations can be turned down to compensate. At these times the electricity we use is very carbon efficient. At other times, especially in the winter where solar generation is low and demand is high, more gas and coal is burnt and the carbon efficiency is worse. For our calculation we’ll use the 2020 average, which is 181g of CO2 per KWh.
This is actually a pessimistic estimate as it’s likely an electric car will be changed at night, when the carbon efficiency tends to improve because electricity demand drops. On top of that, the electricity grid will emit less and less carbon dioxide over time as more renewable generation is brought online. Over the lifespan of a new electric car, the average grid carbon efficiency is likely to be significantly better than today.
A typical electric car, driven reasonably well, should hope to get about 4 miles per KWh. This means an electric car will emit around 45g of CO2 per mile. This is significantly better than the 210g of CO2 per mile emitted from a petrol car.
So why is the electric car so much better? Partly this is because some of the energy the electric car uses comes from zero carbon generation, and partly it’s because internal combustion engines in petrol cars are so inefficient. Car engines get hot, really hot! That’s wasted energy. Electric motors are much more efficient.
So how do we combine the embodied carbon with the per mile emissions? A reasonable way to do this would be to divide up the embodied emissions over the lifespan of the car. We should expect a typical car to do at least 200,000 miles before it’s scrapped. This is still the case for electric cars. I’m going to assume that if you buy a new car, you keep it for its whole lifetime. If you don't, and you pass it on after a few years, strictly you should factor the embodied emissions over the miles you’ve driven.
When we factor in the embodied carbon over a lifetime of 200,000 miles, we get the following emissions per mile:
Small electric car: 115g of CO2 per mile
Small petrol car: 253g of CO2 per mile
The electric car still wins, despite the higher embodied carbon due to its battery. Buying the new electric car will reduce your emissions by 54% compared to buying a new petrol car.
So, how efficient would a petrol car need to be before it’s better than an electric car? It turns out that number is 145MPG! So, if you can buy a petrol car that does MORE than 145MPG, then it should result in less carbon dioxide emissions, over it’s 200,000 mile lifetime. BUT, in reality, it needs to be even higher than 145MPG, because over the time it takes to drive 200,000 miles the carbon efficiency of the electricity grid will get better, making the electric car more efficient year on year. The petrol car, if anything, will get less efficient over its lifetime.
What if I already have a petrol car?
So far we’ve been comparing buying a new electric car with buying a new petrol car, and the electric car won hands down. But what if you’ve already got a petrol car that doesn't need replacing. Should you ditch it for a new EV, purely on environmental grounds?
Possibly surprisingly, the answer is probably yes.
The situation has changed slightly from the ‘new vs new’ case above. Now, we can ignore the embodied carbon of the existing petrol car. The car has already been built. The emissions caused by its manufacture are long gone, and there’s no taking them back. All we care about is the emissions from burning the petrol, compared to the total emissions, electricity generation plus embodied carbon, of the new electric car.
Stealing some numbers from above, we can see the electric car has per mile emissions of 115g of CO2 per mile, including its embodied emissions over its lifetime. The petrol car, taking into account only burning the petrol to run it, emits 210g of CO2 per mile. Therefore the electric car is still better, a 45% reduction in emissions! The most carbon efficient way to travel your next 1 mile in a car would be to ditch your petrol car and buy a new electric one.
The number for the petrol car assumes it does 50MPG. So how efficient must your existing petrol car be to justify keeping it. The answer: 91MPG. This is a fair amount lower than the 145MPG we needed from a new petrol car, but it’s still very high, and the same caveats about the electric car getting better over time still apply.
The exact same thing applies to buying a second hand petrol car, versus buying a new electric car. Even if you consider the embodied emissions of the second hand car to be spent, a new electric car is better.
Second hand electric cars
So, what about buying a second hand electric car? This has only been an option in the last few years, as the first generation of electric cars enter the second hand market. Buying a second hand electric car is now a very real option, and it’s very environmentally friendly.
If we apply the same logic as we did for the second hand petrol car, and ignore the embodied emission of the second hand electric car, the only source of emissions from the electric car is the electricity it uses. That drops the per mile emissions down to 45g of CO2 per mile (or even less when the electricity system decarbonises)! For a car of any kind, right now that’s about as good as it gets, and will only get better over time. That represents a CO2 emissions reduction of 79% compared to a second hand (or your existing) petrol car, and 82% compared to a new petrol car.
The numbers get a bit silly now, but for completeness, a second hand petrol car would need to do 233MPG to be more efficient than a second hand electric car, and a new petrol car would have to do 4,200MPG! I told you it gets silly.
Environmental top tip: Buy second hand.
Do I need a car at all?
So the conclusion is fairly straightforward, if you need a car, buy electric. Ideally, second hand electric.
But of course, even a second hand electric car emits CO2 via the electricity it uses. The question you should ask yourself is, do I need a car at all?
Walking and cycling result in basically no carbon emissions at all, once you factor in that humans need exercise to live, and you might as well get it while you travel from A to B, rather than in a gym.
Electric bicycles are truly amazing. For comparison, emissions from an electric bike are as low as 3g of CO2 per mile, and that includes the embodied carbon of the bike AND its battery.
Traveling a mile in a bus can be a very low carbon way to get around, but it depends on a few factors. A full, 90-seater, electric bus, powered by the UK electricity grid emits 6g of CO2 per mile, per person, much less than an electric car. Having said that, a double decker diesel bus, carrying only you and the driver, does a shocking 2,500g of CO2 per mile! So buses are a great option in cities where they’re heavily used.
The emissions from trains vary depending on the type of train. A UK mainline train results in about 80g of CO2 per mile, per person. This attempts to include the embodied carbon of the manufacturer and maintenance of the train and railway infrastructure. This should be compared to the 115g of CO2 per mile number for an electric car, which also included manufacturing emissions. Note though, that no attempt was made to include the construction and maintenance of the road network in any of the car emissions numbers. So when comparing between trains and cars, trains are slightly better than the numbers above suggest.
Flying is, unsurprisingly, terrible. A plane emits approximately 900g of CO2 per mile, per person.
Environmental top tip: Don’t fly - take a train, or cycle if you can.
What else could I spend the money on?
We’ve agreed that buying an electric car is almost certainly a positive thing for the environment, compared to buying, or using, a petrol car. You might have noticed that at no point have we needed to factor in how much a person uses their car, unless of course the answer is none, in which case, don’t buy a car!
The amount you drive has little to do with the per mile emissions from a car. I’ve assumed the less you use a car, the longer it will last, and the longer it will take you to consume its 200,000 mile lifespan. But there is something to think about if you need a car, but drive it infrequently.
If that’s you, you may want to consider if there’s something better to spend your money on. If you only drive a few miles a week, then yes, buying an electric car will reduce the CO2 you emit driving those few miles, but that might have very little impact on your overall carbon footprint. Because of its embodied CO2, a new electric car will take some time to ‘pay back’ the environment for its production emissions. If you don’t drive very much, this could take a long time. You may want to consider if they’re something better you can do to have a greater short term impact.
For example, if you have some money to spend, and you want to reduce your carbon emissions, you might be better off thinking about spending it on your home, before replacing your petrol car. If you have a good south facing roof then installing solar panels might be a better way to spend your money. If you have gas central heating and hot water, maybe look into installing a heat pump.
I’ll leave you with my last environmental top tip:
If you haven’t done so already, work out your carbon footprint. At least then if you do buy an electric car, you’ll know exactly how much carbon you'll be saving.
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