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How would a wholesale switch to electric cars impact emissions?

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We hear a lot about ultra low and zero emissions vehicles and how they’re key to helping the UK achieve its low carbon ambitions – especially given that around 30% of CO2 emissions arise in road transport. But will they really help? And, if so, by how much?

I’ve often wondered what the impact might be of replacing all the current petrol and diesel cars in the UK with electric cars instead, and so decided to check it out and see if the claims about electric vehicles being zero or ultra low emissions actually stack up.

Before I start, let me just say that I recognise that this is a back-of-a-fag-packet assessment. Even still, I think it’s pretty accurate.

Now, it’s true to say that electric cars produce zero exhaust or tailpipe emissions at the point of use, which is a major air quality benefit in congested cities. But because their batteries are charged-up with mains electricity, around 60% of which is presently supplied by coal and natural gas in the UK, they are not totally emissions free.

In fact, it could be argued that electric vehicles simply displace the point source of emissions, shifting the burden from the motorist to the energy sector, as you’ll see.

When researching this piece, I came across a blog maintained by a user of a Nissan Leaf, who had logged miles travelled for 3 months and actual electricity consumed during charging in that same period. Using this real-world data rather than the manufacturer’s laboratory-based predictions, and based on the 12,000 miles a year that the average family car travels in the UK, it suggests a Nissan Leaf will consume around 3,544 kWh of electricity a year.

So let’s imagine all petrol and diesel cars on UK roads were to be replaced by the popular Nissan Leaf, what would the impact be on power sector emissions?

Well, we know that at the end of 2014, there were 29.6 million cars registered in the UK.

Based on driving 12,000 miles a year and consuming 3,544 kWh of electricity each, swapping them all to the Nissan Leaf would result in an extra 104,941,384,000 kWh (104,941 GWh) of grid demand for power.

Based on the current electricity generating mix, and allowing for transmission losses etc, power sector CO2 equivalent emissions run at approximately 0.57 kg per kWh.

Multiplying predicted electric car power demand of 104,941,384,000 kWh by 0.57, we can see that it would give rise to 59,816,588,880 kg of CO2 emissions.

That would typically be expressed as 59.8 MtCO2eq.

By way of comparison, 2014 CO2eq emissions from passenger cars was 68.5 MtCO2eq.

Which means that a wholesale switch to the Nissan Leaf, with the assumptions I’ve used on charging cycles and power consumption to do 12,000 miles a year, would reduce UK CO2 equivalent emissions by only 13% overall.

Here’s another way to think about it: in 2014, the average UK household consumed 4,001 kWh of electricity. Swapping every current petrol and diesel car to a Nissan Leaf would result in additional power demand equivalent to the electricity used by 26.2 million homes.

Of course, in reality, it could be better or worse than I’ve outlined because some motorists will do less than 12,000 miles a year whilst others will do more.

Either way, it’s hard to see how electric cars can currently be described as zero or ultra low emissions vehicles when looked at in this context – that will only be possible in the UK with an electricity mix that consists of significantly less fossil fuel generation. The problem with that, however, is that with renewables only able to provide a comparatively small contribution right now, and nuclear new build still stalled, it’s hard to see how that’s going to happen any time soon, and that’s based on current demand: how we’d meet that current demand, plus a further 104,941 GWh needed to power millions of electric cars, with low carbon power alone poses an even bigger question.

What do you think? Are electric cars the future we should be aspiring to or is there a better way we haven’t considered yet? I’d love to here your views in the comments below.

7 Comments

  • Lee Petts says:

    So, after authoring this post, I was asked how many wind turbines it would take to supply the power required to charge a nation of electric cars if we were to switch away from petrol and diesel cars on a wholesale basis.

    I’ve calculated this two different ways.

    The first way, I started by assuming a turbine with a 2.5 MW capacity and a capacity factor of 30%, to estimate that annual output per wind turbine would be 6.57 GWh or 6,570,000 kWh. If I’m right in my assessment that a Nissan Leaf will consume 3,544 kWh of power a year to do 12,000 miles, then a single wind turbine could theoretically power 1,853 such cars. But we’d need to power 29,611,000 cars in total. By dividing that into 1,853 cars per wind turbine, I calculate that we’d need a total of 15,980 wind turbines.

    The second way, I took the total onshore and offshore wind output in 2014 of 32,015 GWh and divided this into the some 6,600 wind turbines we have to get an annualised output per turbine in the real world. That gets us to a lower figure of 4.85 GWh per turbine or 4,850,000 kWh that could power 1,368 cars. Scaled-up to the charging demand of 29,622,000 cars using these figures and we can see that it would require 21,645 wind turbines.

    Whether it’s 15,980 or 21,645, it’s an awful lot of wind turbines.

  • Joe Public says:

    Have you factored-in UK wind’s variability?

    Annual performance is a just a number; there will be prolonged periods when there’s insufficient wind over many days.

    Whilst the number of UK turbines is now ~6,691, the wind pattern won’t have changed much.

    https://pbs.twimg.com/media/CUwFqsoWoAA7vmO.png:large

  • Joe Public says:

    Thanks for the rapid response, Lee.

  • NomadicOne says:

    I’ve just read that Associated British Ports is to spend £3m on a single wind turbine. So if your analysis is correct about the number of wind turbines it would take to charge all these electric cars, the cost of building all the wind turbines would be colossal – ranging from £47.9 billion (15,980 turbines) to £64.9 billion (21,645 turbines)!!!

    • Lee Petts says:

      Thanks for commenting NomadicOne! To be fair, installing several wind turbines as part of a single wind farm scheme could reasonably be expected to lower the unit rates costs of each turbine, but even still, the cost of building between 16,000 and 22,000 wind turbines would still run to tens of billions.

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