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Update July 2, 2020: Lifecycle emissions data revised to reflect the latest data on electricity carbon intensity and battery manufacturing.
Electric vehicles (EVs) are an important part of achieving global climate change goals.They feature prominently in mitigation pathways to limit warming well below 2C or 1.5C, which would be in line with the goals of the Paris Agreement.
However, while electric vehicles do not emit greenhouse gases directly, they run on electricity, which is still largely generated from fossil fuels in many parts of the world.Energy is also used to make vehicles, especially batteries.
Here, Carbon Brief details the climate impact of electric vehicles in response to recent misleading media coverage on the subject.In this analysis, Carbon Brief found:
There is also considerable uncertainty about emissions associated with EV battery production, with different studies producing widely varying numbers.As battery prices fall and automakers begin to adopt larger batteries with longer ranges, battery production emissions could have a bigger impact on the climate benefits of EVs.
About half of battery production emissions come from the electricity used to manufacture and assemble batteries.Producing batteries in regions with relatively low-carbon electricity or in factories powered by renewable energy, like those used in the best-selling Tesla Model 3, can drastically reduce battery emissions.
A recently published working paper by a group of German researchers at the Institute for Economic Research (ifo), a think-tank, found that “electric vehicles will hardly help reduce CO2 emissions in Germany in the coming years”.It shows that in Germany, “in the best-case scenario, the CO2 emissions of electric vehicles are slightly higher than those of diesel engines”.
The study was reported by international media, and the Wall Street Journal published an editorial titled “Germany’s Dirty Green Cars.”It also drew resistance from EV advocates, with articles on Jalopnik and Autoblog and individual researchers refuting the claim.
Other recent studies of electric vehicles in Germany have come to the opposite conclusion.One study found that electric vehicles emit 43 percent lower emissions than diesel vehicles.Another detailed that “electric vehicles have a lower lifetime climate impact than ICE vehicles in all cases examined”.
These differences stem from assumptions used by the researchers.As Professor Jeremy Michalek, Director of Carnegie Mellon University’s Vehicle Electrification Group, told Carbon Brief, “Which technology stands out depends on a lot of things”.These include which specific vehicles to compare, hypothetical grid combinations, whether marginal or average electricity emissions are used, hypothetical driving patterns, and even the weather.
The graph below, adapted from an analysis by the International Council on Clean Transportation (ICCT), shows life cycle emissions estimates for a typical European conventional (internal combustion engine) vehicle, a hybrid conventional vehicle with the best fuel economy (2019 Toyota Prius Eco ) and Nissan Leaf EVs are available in individual countries, as well as the EU average.[The Leaf was the best-selling electric car in Europe in 2018.]
The chart includes tailpipe emissions (grey), fuel cycle emissions (orange) – including oil production, transportation, refining and power generation – emissions from manufacturing non-battery components of vehicles (dark blue) and conservatively estimated emissions from manufacturing batteries (light blue) color).
In most countries, the majority of emissions from EVs and conventional vehicles over their entire life cycle come from the operation of the vehicle — the tailpipe and the fuel cycle — rather than the manufacture of the vehicle.The exception is that in some countries – such as Norway or France – almost all electricity comes from near-zero carbon sources, such as hydroelectric or nuclear power.
However, while not reducing the carbon emissions from burning a gallon of gasoline or diesel, electricity does not.In countries such as France (where most of the electricity comes from nuclear power) or Norway (from renewable energy), EVs have much smaller life-cycle emissions.
The graph above calculates EV emissions based on each country’s current grid mix.However, if the climate targets set out in the Paris Agreement are to be met, electricity generation will be significantly less carbon-intensive, further enhancing the advantages of electric vehicles over conventional vehicles.
In the UK, for example, electricity generation emissions have fallen by 38% in the past three years alone, and are expected to drop by more than 70% by the mid-to-late 2020s, which is exactly within the life cycle of an EV purchased today.
Emissions associated with battery production are from the latest (2019) estimates from the IVL Swedish Institute for the Environment.The Nissan Leaf analyzed here has a 40-kilowatt-hour (kWh) battery, while the Tesla Model 3 is available in either 50kWh or 75kWh options (a 62kWh option was previously available, but has been discontinued).
The graph below shows the estimated lifetime emissions of a Model 3 if the battery were produced in Asia – where most of its electricity comes from coal – like the Nissan Leaf battery.The long-range 75kWh model was used in this analysis to mimic the approach in the ifo study; the mid-range 50kWh model will reduce battery manufacturing emissions by about a third.
Under these assumptions, the Tesla Model 3′s lifetime greenhouse gas emissions would be higher than Germany’s highest-rated conventional car, but still more climate-friendly than the average car.In other countries, even the long-range Tesla Model 3 emits lower emissions than any gasoline car.
However, the fact that Tesla batteries are actually made in Nevada has an important impact on this calculation.As discussed later in this article, U.S.-produced batteries tend to have significantly lower life-cycle emissions estimates than Asian-produced batteries.
About 50% of battery life cycle emissions come from the electricity used in battery manufacturing and assembly, so producing batteries in factories powered by renewable energy (as was the case at the Tesla factory) greatly reduces life cycle emissions.The graph below shows Carbon Brief’s estimate of lifetime emissions from a Tesla Model 3 using batteries produced in Tesla’s “Gigafactory.”
A Model 3 with a 75kWh battery produced at the Nevada Gigafactory has significantly reduced emissions and has a similar life-cycle climate impact to the Nissan Leaf’s estimates, given manufacturing conditions.
Electricity generation emissions will also vary from country to country, with some regions having a cleaner generation mix than others (and correspondingly, the climate advantage of EVs is greater).
The numbers shown above adjust emissions from conventional and electric vehicles to reflect real-world driving conditions, not the number of test cycles.This is important because official fuel economy estimates can differ significantly from real-world performance, with large knock-on effects on comparisons of conventional and electric vehicles.
The analysis in the graph above is based on a total mileage of 150,000 kilometers, comparing EVs and conventional vehicles over their entire life cycles.
However, it is also possible to compare vehicles over time to see how long it will take to pay off the initial “carbon debt” incurred by producing carbon-intensive battery packs for electric vehicles.
For example, as mentioned above, a new Nissan Leaf EV bought in the UK in 2019 will have lifetime emissions around three times lower than the average new conventional car.
Over time, as shown in the graph below, this excess carbon debt will be paid off after less than two years of driving, although batteries will result in higher emissions during a “zero-year” car manufacturing process.
Cumulative GHG emissions of an average new conventional vehicle and a new Nissan Leaf.These figures are in life-cycle CO2-equivalent tonnes, assuming 150,000 km over a 12-year lifespan.EV fuel cycle emissions are based on the carbon intensity of electricity in the UK for the first year in 2019, and are progressively increased to the 2030 target of 100gCO2/kWh and beyond.Carbon Brief chart made with Highcharts.
The graph above shows that use-phase emissions vary widely, with EVs saving around 2 to 3 tonnes of CO2e per year in the UK.(This number has dropped over time as the power mix gets cleaner).
This means that even if a new electric car replaces an existing conventional car, it will still start to reduce emissions after less than four years of use compared to continuing to run the old car, as shown in the graph below.
The equation becomes much clearer without the generous assumption that existing conventional cars emit the same amount of emissions as the average new car.
Note that the cumulative lifetime emissions chart above is based on 150,000 kilometers over 12 years, or about 7,800 miles per year, to be consistent with the rest of this article.
That figure is slightly higher than the UK’s average annual mileage, which fell to nearly 7,100 miles in 2017.However, even at this lower mileage, replacing existing conventional cars with EVs will start reducing emissions in just four years.
The ifo study provides an example of the potential pitfalls of using test cycle fuel economy values rather than actual performance.The study compared the lifetime emissions of a Mercedes C 220 with the new Tesla Model 3, taking into account emissions associated with vehicle production.The study found that Tesla’s emissions over the lifetime of the vehicle are 90 to 125 percent those of Mercedes’.
In other words, despite the headlines it generates, even ifo finds that EVs range from slightly better to slightly worse than diesels.
The study assumed a Mercedes fuel economy of 52 miles per gallon (mpg), significantly higher than the average car in the US (25mpg for petrol) but similar to the UK average (52mpg for petrol) diesel at 61mpg).However, different fuel economy testing procedures can produce wildly different results.
While US EPA fuel economy figures tend to reflect actual driving conditions, the New European Driving Cycle (NEDC) values used in the EU overstate actual vehicle fuel economy by up to 50%, possibly even more for Mercedes vehicles.
By comparison, the Tesla Model 3 energy usage assumed in the study (241 watt-hours per mile) was only 8 percent less than the EPA’s estimated actual usage (260 watt-hours/mile).Using more realistic fuel economy estimates for conventional vehicles will have a large impact on the results of the ifo analysis, making EV options preferable to conventional vehicles.
Both the ifo study and the ICCT analysis rely on the same estimates of emissions from battery manufacturing: a 2017 study by the Swedish Institute for the Environment (IVL).The IVL examined studies published between 2010 and 2016 and concluded that battery manufacturing emissions could be between 150 and 200 kilograms of carbon dioxide equivalent per kilowatt-hour of battery capacity.
Most of the studies reviewed by IVL focused on battery production in Asia, not the US or Europe.The IVL study also noted that battery technology is developing rapidly and has great potential to reduce manufacturing emissions.
The IVL study received considerable criticism and was significantly revised in late 2019.IVL researchers now estimate that battery manufacturing emissions are actually between 61 and 106 kilograms of carbon dioxide equivalent per kilowatt-hour, capped at 146 kilograms.The low-end estimate of 61kg is for the case where the energy used in battery manufacture comes from zero carbon sources.IVL said the revision was driven by new data on battery production, including more realistic measurements of energy use at commercial-scale battery factories that have expanded significantly in size and output in recent years.
Carbon Brief conducted its own assessment of the literature to find recently published estimates of life cycle emissions from battery manufacturing.The graph below shows data from 17 different studies, seven of which were published after the 2017 IVL estimate.It divides the study according to the region where the battery is produced: Asia (red), Europe (light blue), the United States (dark blue) and examining reviews of multiple regions (grey).
Most studies published in recent years show that life cycle emissions are smaller than those in the original IVL study, averaging around 100 kg CO2 per kWh for studies published after 2017.These new estimates are in line with revised 2019 IVL research figures. Manufacturing emissions estimates in Asia are typically higher than in Europe or the US, reflecting the region’s widespread use of coal for power generation.Studies that directly compared batteries made in Asia to those made in the US or Europe found that outside Asia, life cycle emissions were reduced by about 20%.
Many studies break down emissions into mining, refining and other material production that occurs off-site, and the actual manufacturing process of assembling batteries.They tended to find that about half of the lifecycle emissions were the result of off-site material production, and half were the result of the electricity used in the manufacturing process.The table below shows this, taken from the 2017 IVL report, which breaks down lifecycle emissions by component and manufacturing stage.
“Manufacturing represents a large part of the impact on production … which means the location of production and/or the mix of electricity has a large potential to affect the outcome.”
That’s an important factor to consider when estimating battery emissions from Tesla’s Gigafactory in Nevada, which produces all of the batteries currently used in Model 3 vehicles.
The average carbon intensity of electricity in Nevada, where the Tesla Gigafactory is located, is about 30 percent lower than the U.S. average.As the chart below shows, Nevada has phased out nearly all coal-fired power generation over the past two decades.
Tesla recently started building the world’s largest solar roof atop its Gigafactory, which, combined with battery storage, should provide nearly all the electricity the facility uses.
Post time: Jun-13-2022
