Rebuttal to the opinion of Christoph Buchal, Hans-Dieter Karl and Hans-Werner Sinn titled “Coal Engines, Wind Engines and Diesel Engines. What does the CO2 balance show?”
A recent opinion piece by Buchal, Karl and Sinn claims a Tesla Model 3 emits 11% to 28% more CO2 over its lifetime than a Mercedes C 220 diesel. Correcting the errors in their calculation reveals that the electric vehicle (EV) emits 63% less.
Replacing the flawed NEDC test with real-world values increases diesel emissions with 80 grams of CO2 per km driven (abbreviated ‘gr’) while electric emissions only increase 15 gr.
Replacing an outdated study on battery production with new studies and taking into account the Tesla Gigafactory runs on renewable energy reduces battery emissions from 85 to 33 gr. Increasing the battery lifespan to 300 thousand kilometres reduces battery emissions to 16 gr.
Replacing the current German energy mix with the energy mix over the lifetime of the vehicle reduces driving emissions of the electric vehicle from 97 gr to 66 gr.
The end result is that emissions from the Mercedes C 220 diesel increase from 141 gr to 221 gr, while the emissions of the Tesla Model 3 decrease from 167 to 83 gr.
Recently Buchal, Karl and Sinn (I’ll abbreviate to BKS) published a much-cited ‘study’ claiming Diesel cars emitted less CO2 over their lifetime than electric vehicles. My impression was that it was basically a list of over-the-top worst-case assumptions for the EV in an attempt to make the Diesel look good, produced by people with limited knowledge of electric vehicle research. I pointed that out on twitter and many others also rebutted the opinion piece.
But now the authors are back, with a blog post titled Erläuterungen zur Studie “Kohlemotoren, Windmotoren und Dieselmotoren. Was zeigt die CO2-Bilanz?”. They basically double down on everything.
It would be tempting to ignore them, because although the writers where respected scientists during their active careers, they never researched electric vehicles. So, as far as I’m concerned, these are the non-peer reviewed opinions of laypersons. But Hans Werner Sinn is a famous economist in Germany and the conclusion was remarkable so it got a lot of traction in the popular press. Since I am a scientist who researches this at the Eindhoven University of Technology, I feel responsible for keeping the public debate free of blatant errors. So I wrote this blog post to remove the biggest errors.
First, let’s quickly set the scene. A long range Tesla Model 3 and a Mercedes 220 diesel are going head to head: which car emits more CO2 over its lifetime? Problems for the diesel: it emits more in real life than in the lab and you must not forget to include the production of diesel. Problems for the electric car: producing the battery emits CO2 and the German electricity mix is dirty. Which car will win?
BKS made a convenient list of criticisms in the blog post where they doubled down. I will follow their questions. I translated the questions to English and abbreviated their answers. (You can look at their blog post for their entire answer.) Then I added my own answers and an explanation. I hope you want to follow along.
1. Did we overlook the importance of EVs for air quality in the city?
BKR’s answer: no, and we don’t mind electric city vehicles at all, but we compared regular cars.
My answer: you overlooked Dieselgate and 5,000 deaths per year.
So someone complains to BKR that Diesel cars are emitting deadly NOx in the city and they are ignoring that. (Diesel cars are estimated to cost 5,000 deaths per year) And BKS basically reply they are fans of small electric city cars and electric scooters but they are comparing long distance cars here. Well, I’m a fan of small electric city cars, electric scooters too! (And I like bicycles even more because I’m Dutch.) But that does not alter the fact we are comparing cars here so let’s stop deflecting.
And most people are aware by now that diesel has a problem. They look great in the lab after carmakers are done tricking the test but on average, diesel cars pollute 4.5 times more than they are allowed to in real life. (Mercedes is average.) BKR could have mentioned some of that.
2. Did we overlook the usefulness of car batteries in a grid running on wind and solar?
BKR’s answer: we did mention green methane and hydrogen but you can’t use car batteries for seasonal storage.
My answer: you seem unaware EVs are extremely useful for daily grid management.
The picture shows some attributes of one of our models (page here, the movie is in Dutch, unfortunately).
Explanation: it’s my job as a researcher to model future electricity grids. Among us (energy modellers) it’s well known that you basically need two new types of storage to deal with solar and wind: daily and yearly. Saying EVs are useless as seasonal storage is beside the point and nobody in his right mind uses batteries (in- or outside a car) for that. But EVs are a godsent as daily storage and variable load. That means they can use wind and solar when all other demand is gone. This improves the business case of wind and solar and strongly reduces the additional amount of stationary battery you have to produce and buy.
What variants of the Tesla did we compare?
BKR’s answer: we took the one with the range closest to the diesel vehicle.
My answer: this is the biggest battery in this price range. Why not take an average one?
Explanation: I’m not saying this is an error. But it’s certainly not average. Maybe it would have been good if BKR reminded people that the 75 kWh battery they chose constitutes the biggest battery in this segment and that the Model 3 also comes with a 50 kWh battery (335 km real range).
3. Why didn’t we use WLTP?
BKR’s answer: because Tesla did not have a WLTP value yet.
My answer: if we take real-world energy use, the emissions from the Mercedes increase 80 gr and become 221 gr. The Tesla only increases 15 gr to 182 gr. The diesel is already lagging 40 gr after the first correction.
Explanation: to make it possible to compare cars in an objective fashion, the world uses standardized tests. In Europe it used to be the NEDC (New European Driving Cycle). But the difference between the NEDC and reality continued to grow, mostly because car makers are in charge of the tests and they learned to employ more and more tricks. On overage, modern vehicles (from after 2015) emit 40% more CO2 in reality than in the NEDC test. How do we know this for sure?
- There are dozens of studies by serious research institutes (like the ICCT report above) that compare NEDC with official road tests and they all show the same: the gap between NEDC and real use is becoming wider and wider.
- In America, it’s not the carmakers but an independent organisation (the EPA) that tests the CO2 exhaust and (surprise!) in the US the numbers are pretty realistic.
- There are many sites with users keeping track of their energy use. E.g. the German spritmonitor.de.
The successor of the NEDC is the WLTP (Worldwide Harmonized Light Vehicle Test Procedure) and it is somewhat closer to reality. But there is already evidence for cheating, which is to be expected since tests are still done by manufacturers themselves. So basically everybody in the industry knows you have two types of tests: tests done by the manufacturers themselves (NEDC and WLTP) and tests done by independent bodies (e.g. EPA and ICCT).
So, did BKR want to compare realistic values? Or did they want to compare incorrect numbers that make diesel look good? Maybe they were unaware of the problem at first but their unwillingness to take more realistic values after this has been pointed out to them is troubling.
Taking realistic energy use values from spritmonitor.de the Mercedes C 220 d CO2 emissions jump 80 grams from 141 gram CO2/km to 221 gram CO2/km. The Tesla Model 3 also increases but only 15 grams from 167 to 182 grams. We could also take new road tests done in Europe or the numbers from the American Environmental Protection Agency and the results would be similar. Approximating real-world use is only hard if you are a car manufacturer that wants to pretend your car uses less than it really does. Taking real life energy use immediately puts the Diesel at the disadvantage. But we are just getting started!
5. Did we take too much CO2 emissions for battery production?
BKR’s answer: of course not! We used the really good meta-study from Romare and Dahllöf (the Swedish study).
My answer: the Tesla Gigafactory doesn’t emit 170 kg of CO2 per kWh of battery but 65 kg. This lowers the battery CO2 emissions per km from 85 to 33. The Tesla now emits 130 gr vs. 221 for the Merc.
The ‘Swedish study’ is the go-to source for EV sceptics because of its unrealistically high values for CO2 emissions for battery production. Based on this, BKR assumed between 145 and 195 kg CO2 (let’s average it at 170) will be emitted for every kWh of battery produced. They based that on a study that managed to rile up a lot of people a few years ago and has been corrected several times. Here’s one example in Handelsblatt. The authors also felt compelled to point out battery manufacturing is rapidly advancing and their study should not be used to predict future battery emissions like BKR are doing now. This is, of course, to be expected: as batteries get lighter they use less material and as competition grows fiercer, bringing down energy expenses is important.
Elon Musk called the Swedish study ‘clueless’ and pointed out much less energy is required per kWh of battery and his factory is running on renewable energy anyway. Now you might hate Elon Musk but he does have the biggest battery factory on earth and more specifically the one where the Model 3 that BKR is talking about is made. You know, the one that will be covered in solar cells and with enough windmills next to them to make produce all the energy the factory needs. Tesla has told the world repeatedly that Tesla already buys 100% green energy and that the factory will use only renewable electricity specifically built for the factory in 2019. (Of course, using “Elon Time” that could become 2020 of 2021.)
Partly as a reaction to the Swedish study, FFE did a follow-up study called “Carbon footprint of electric vehicles – a plea for more objectivity“, incorporating the reactions of the authors after the study and looking into the future. The study concludes that right now 106 kg/kWh is a better estimate. However, this gets to 65 kg/CO2 for a factory running on renewable energy like the Tesla Gigafactory. I might add that mineral extraction could also be done with electric vehicles and other electric machinery running on renewable energy and this would slash that 65 kg/kWh number in half once again. And if we take the second life of the battery and recycling into account, things look much better still. A study from February 2019 by Maeva Philippot et. al. (from the crack research group from Joeri van Mierlo at the Vrije Universiteit Brussel) concludes that “Optimizing the process by reducing the electricity consumption during the manufacturing is also suggested, and combined with higher pack energy density, the impact on climate change of the pack manufacturing is as low as 39.5 kg CO2 eq/kWh.”
Now, why in heaven’s name would BKR take this oft corrected study and not a more recent one? I won’t speculate but let’s just say the numbers are outdated. For the Tesla Gigafactory the best estimate is not 145-195 but 65 kg of CO2 per kWh of battery. (Also congruent with industry sources of mine.) And in the future, that number might easily go below 40.
6. Should you take battery production using green energy into account?
BKR’s answer: no, you have to take the average because otherwise you just take away green electricity elsewhere.
My answer: if you compare with a Tesla Model 3 you should certainly do so.
We have already covered this above. Tesla claims to already produce the batteries using green energy from wind and solar. (The Nevada mix phased out almost all coal between 2004 and 2015 by the way.) They are currently on track to get all energy from their own combination of solar, wind and batteries within a few years. Not counting that as produced using green electricity would be ludicrous.
And let’s take the reasoning of BKR to its logical conclusion: you can buy green energy, you can buy stakes in a windmill next to your door and you can even buy solar panels for your roof. It’s all to no avail. Only nationwide policies can apparently make a difference and there is nothing anyone individually can do. I find that a very gloomy, unempowering, status quo friendly reasoning. I’ll count my own solar panels as self-induced green energy, thank you very much. But apart from that discussion the Tesla Model 3 is soon produced by the factories own renewable electricity so not counting that is simply wrong.
Did we exaggerate the CO2 emissions of the German electricity mix?
BKR’s answer: no we didn’t.
My answer: a conservative best estimate over the lifetime of the vehicle is 375 gram/kWh, not 550. This lowers Tesla emissions by 31 gr. The Tesla now emits 99 gr. and the Merc 221 gr.
In the quest to reduce CO2 emissions, many things happen at the same time. Two very much interconnected things are the transition from diesel cars to electric vehicles and the transition from coal to gas, solar and wind. The one trick that literally every EV opponent uses is to assume that nothing will happen on the coal front. So not only do they take the currently high-CO2 German mix but they also assume the mix will not become better over the lifetime of the vehicle.
That’s a strange assumption because there are German laws about that, requiring 40% renewable electricity in 2025, 55% in 2035 and 80% in 2050. The coalition contract of the current CDU-CSU-SPD government even has a target of 65% by 2030. A German energy modelling colleague recommended this study for the German ‘Stromsektor 2030’. It estimates the grams per kWh in 2030 in three scenarios:
- BAU (business as usual): 413 gr
- KA (Kohleausstieg): 335 gr
- KA65 (Kohleausstieg with 65% renewable electricity), the current government policy, 310 gr
Now we can argue about which number is most realistic but assuming the current 550 gr will remain over the lifetime of the vehicle (as BKR do) is clearly simplistic and wrong. I propose we assume the car will drive 17 years (it’s 19 in the Netherlands) until it’s 2036. I estimate the mix in 2036 will be below 200 gr CO2 per kWh. If we average the difference between 550 and 200 we get 375 grams. I’m not saying it’s a perfect value but I think it is a lot more realistic than the number assumed by BKR.
Since the Tesla uses 0,177 kWh per km (see step 4), reducing the energy mix from 550 to 375 lowers the emissions per km from electricity from 97 (=550*0.177) to 66 (=375*0.177).
8. How long does an electric battery last?
BKR’s answer: car manufacturers claim unrealistic numbers like 300k but we took a realistic 150k.
My answer: the battery will last over 600k km, but let’s ignore second life and recycling and assume it is scrapped with the car after 300k km. This halves battery emissions to 16 gr. The Tesla now emits 83 gr. and the Merc 221.
First, let’s look at what 150k means. If a Tesla with a 485km real life range were to drive 150 000 km (as BKR proposes) that would constitute 310 cycles.
In reality, modern batteries like the Samsung battery in the BMW i3 are rated for 4600 cycles. For the Tesla Model 3 that would constitute 485*4600 = 2.2 million kilometres.
In real life, the performance is less but the quality of batteries is evolving rapidly. Real world tests of Tesla batteries by actual owners show that they will last between 500k and 1000k km. If BKR are really interested in battery degradation, I propose they start by reading some 2018 sources here, here, here, here, here, here, here and here. Bottom line: battery developments happen incredibly fast and tomorrows batteries will last even longer than today’s batteries that already last about ten times longer than what BKS are assuming.
Pinning down a better number is much harder. An electric car’s motor and battery will probably outlast the rest of the car. So after how many km will the car be retired? Hard to say but we know Tesla Model 3 cars are driven more km than average because of their low cost per km: the comparison to diesel cars is apt. In the Netherlands, 300k is a low estimate for a diesel and I would guess people in Germany don’t drive less. So I propose 300k as a conservative number.
9. Don’t we have to include the diesel motor production?
BKR’s answer: Nah, it’s a wash.
My answer: Nah, it’s a wash. We agree!
10. Do electric cars come off badly in our study?
BKR’s answer: on the contrary because diesels have more range, chargers use energy, heating EVs costs energy and we even took diesel production into account.
My answer: by correcting the errors in your study, the energy use of the diesel car increased from 141 to 221 gr while the emissions of the electric vehicle decreased from 167 gr to 83 gr. So the EV went from 10 to 25% worse in your study to 62% better after correction.
Strange that BKR want to mention once again they didn’t forget to include the production of diesel. Let me just say: I don’t want to make an issue, of course, you have to include diesel production and unsurprisingly you took a pretty low estimate.
Energy for cooling of chargers is negligible: it’s loud but doesn’t use that much energy compared to the 100kW that is delivered. Heating of EVs takes some energy but it’s pretty negligible too. BKR were right to ignore those too.
So let me sum up the answer to this question by looking at all BKRs questions (every line corresponds to the question with the same number):
- BKR ignored air pollution.
- BKR ignored the usefulness of EVs in stabilizing a grid on wind and solar.
- BLR took the biggest battery in this price range.
- BKR took unrealistically low energy use, helping the diesel.
- BKR took unrealistically high battery production emissions, hurting the EV.
- BKR ignored that Tesla batteries are made using green electricity.
- BKR ignored that the electricity mix will become greener over the EVs lifetime.
- BKR underestimated the lifetime of the battery.
So yes, I think it is safe to say electric cars came off badly in this study.
REMARK / UPDATE:
The first version of this article erroneously stated MtCO2/a instead of grCO2/kWh for the KA and KA65 scenarios en referred to European laws about renewables where it should have been German laws about renewable electricity. This has been corrected and the text directly below it has been updated to reflect the correction.
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