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Energy transition: recycling materials to preserve resources

What is the carbon footprint of electric bikes?

Anne De Bortoli, Carbon neutrality researcher at Polytechnique Montréal
On December 5th, 2023 |
4 min reading time
Anne de bortoli
Anne De Bortoli
Carbon neutrality researcher at Polytechnique Montréal
Key takeaways
  • The market for electrically assisted bicycles (EABs) is growing rapidly, and by 2030 almost 55% of bicycles sold in Europe will be electric.
  • The carbon footprint of this mode of transport is smaller: an average of 13g CO2e/km travelled, compared with 60 to 75g CO2e/km travelled by an electric city car.
  • Most (94%) of the GHG emissions from an electric bicycle come from its manufacture, in particular the manufacture of the aluminium frame.
  • The most energy efficient EAB is obtained by “retrofitting”, i.e. transforming a second-hand standard bike.
  • To reduce its carbon footprint even further, there are several solutions to consider (alternatives to aluminium, different types of batteries, etc.).

Electrically-assisted bicycles (EABs) are on a roll: in 2020, 20% of bicycles sold in Europe (4.5 million) were electric, and this figure is expected to rise to 55% by 20301. So, let’s get to the heart of the matter: is it a problem for the climate?

Com­pared with many oth­er modes of trans­port… Of course not! In France, the car­bon foot­print of an elec­tric bicy­cle aver­ages 13 grams of CO2 equiv­a­lent (CO2e) per kilo­me­tre trav­elled, if the vehi­cle is used for 20,000 km. This fig­ure rep­re­sents the entire life cycle of the bicy­cle: man­u­fac­ture, use, main­te­nance and end of life. All the green­house gas­es (GHGs) emit­ted are includ­ed – which is why we talk about CO2 equiv­a­lent. The impact of an EAB is slight­ly greater than that of a mus­cle bike, which has a car­bon foot­print of 10 to 12g of CO2e/km travelled.

But these forms of trans­port are among the most effi­cient in terms of all envi­ron­men­tal fac­tors. In France, the car­bon foot­print of an elec­tri­fied train is esti­mat­ed at around 35g of CO2e/km trav­elled per pas­sen­ger. This ris­es to 60–75g of CO2e/km trav­elled for an elec­tric city car. Inter­nal com­bus­tion cars and aero­planes exceed the 100g CO2e/km mark. Only walk­ing (1 to 2g of CO2e/km trav­elled) and the Paris metro and RER (8 to 10g of CO2e/km trav­elled) are more effi­cient than cycling. It is esti­mat­ed that buy­ing and using an elec­tric bicy­cle in France has a bet­ter car­bon foot­print than using a com­bus­tion-pow­ered car in the city, as long as the bicy­cle is used for more than 1,000 km before being recycled.

Can’t the good results achieved by electric bikes in France be explained by our low-carbon electricity mix?

When I worked on this sub­ject 7 years ago, I found that the foot­print asso­ci­at­ed with the use of elec­tric micro-mobil­i­ty was mul­ti­plied by three in Chi­na. Since then, the Chi­nese elec­tric­i­ty mix has been decar­bonised and the dif­fer­ence is small­er, but still sig­nif­i­cant. In Ger­many, elec­tric­i­ty pro­duc­tion cur­rent­ly emits 10 times more green­house gas­es than in France. But in the end, the impact on the total car­bon foot­print of an ECV is mod­er­ate, because an ECV con­sumes lit­tle elec­tric­i­ty, while its man­u­fac­ture accounts for the major­i­ty of GHG emis­sions over its life cycle. The total car­bon foot­print climbs from 13g CO2e/km trav­elled in France to 17g CO2e/km trav­elled in Germany.

Why is the manufacture of ECVs the biggest source of GHG emissions over their entire life cycle?

Man­u­fac­tur­ing accounts for 94% of the total car­bon foot­print of an ECV dri­ven 20,000 km in France2. For a 20kg alu­mini­um bicy­cle (exclud­ing elec­tric assis­tance) man­u­fac­tured in Chi­na, the pro­duc­tion of the frame emits 181kg of CO2e. Man­u­fac­tur­ing the bat­tery emits 20 kg of CO2e and the motor 37 kg of CO2e. The biggest source of green­house gas emis­sions from an ECV is there­fore linked to the man­u­fac­ture of the frame. Alu­mini­um is the cul­prit. Chi­na is the world’s lead­ing pro­duc­er of refined alu­mini­um: the coun­try pro­duces almost half the world’s alu­mini­um3. Even though Chi­na is reduc­ing the car­bon foot­print of its elec­tric­i­ty mix, alu­mini­um refin­ing is still a major emit­ter of green­house gas­es. This is the biggest con­trib­u­tor to the car­bon foot­print of an ECV. Assem­bly real­ly does have a lim­it­ed impact, so a “made in France” bike is of lit­tle inter­est in terms of car­bon foot­print unless the met­al in the frame is refined in a coun­try where the elec­tric­i­ty mix is low in car­bon (e.g. French, Que­be­cois or Ice­landic aluminium).

The impact of bat­ter­ies there­fore seems negligible…Batteries get a bad press because of elec­tric cars. But an elec­tric car car­ries sev­er­al hun­dred kilos of bat­ter­ies. The bat­tery in an elec­tric bicy­cle weighs just a few kilos. The green­house gas emis­sions gen­er­at­ed by these bat­ter­ies are com­par­a­tive­ly low.

How­ev­er, they are dif­fi­cult to assess pre­cise­ly. We analysed around thir­ty pub­li­ca­tions on lithi­um-ion bat­ter­ies, and the car­bon foot­print per kWh varies by a fac­tor of 10.There is a lot of uncer­tain­ty about the con­di­tions under which the met­als are extract­ed from the mine and refined. It is dif­fi­cult to obtain reli­able indus­tri­al data. That does­n’t change the fact that frames account for the largest share of emis­sions. What’s more, we can con­sid­er that the most fuel-effi­cient EAB is a mus­cle bike – with­out elec­tric­i­ty – that is already in use, and that we are going to fit with an elec­tric assis­tance sys­tem. This is also known as retro­fitting. It’s an extreme­ly inter­est­ing solu­tion for avoid­ing the need to build a new frame.

What are the other sources of GHG emissions from an ECV?

That depends on the coun­try. Main­te­nance accounts for around 8% of GHG emis­sions over the entire life cycle of a bicy­cle in France. Elec­tric­i­ty con­sump­tion aver­ages 1 kWh per 100 km, i.e. 0.5 g of CO2e/km trav­elled in France (i.e. around 4% of total EAB emis­sions) or 5 g of CO2e/km in Ger­many (i.e. 29% of total EAB emissions).It depends, of course, on the bike, the user, the topog­ra­phy and changes in the elec­tric­i­ty mix.

As far as end-of-life is con­cerned, recy­cling bat­ter­ies and mate­ri­als can reduce the car­bon foot­print by 6% in France. Unfor­tu­nate­ly, less than 8% of bat­ter­ies in ECBs are cur­rent­ly recycled.

Is it possible to reduce the carbon footprint of ECVs?

The var­i­ous levers men­tioned above – more recy­cling and the retro­fitting of mus­cle bikes – are vir­tu­ous prac­tices in this respect. The longer a bike lasts, the small­er its car­bon foot­print per kilo­me­tre travelled.

As the frame is the ele­ment that has the biggest impact, we then need to work on it. For exam­ple, it is pos­si­ble to turn to alter­na­tive alu­mini­um pro­duc­ers, such as Que­bec. Using alter­na­tive mate­ri­als such as steel and wood is also an inter­est­ing lever. Final­ly, a great deal of research is being car­ried out on bat­ter­ies. With col­leagues, we are cur­rent­ly assess­ing the impact of using oth­er types of bat­ter­ies (such as sodi­um-ion bat­ter­ies and sol­id elec­trolyte bat­ter­ies) on the car­bon foot­print of elec­tric vehi­cles. The results are very encouraging.

Anaïs Maréchal
1Deloitte, 08/2021, Con­sumer sec­tor brief­ing : E‑bikes on the fast track, disponible ici : https://​www2​.deloitte​.com/​c​o​n​t​e​n​t​/​d​a​m​/​D​e​l​o​i​t​t​e​/​d​e​/​D​o​c​u​m​e​n​t​s​/​c​o​n​s​u​m​e​r​-​b​u​s​i​n​e​s​s​/​S​e​c​t​o​r​-​B​r​i​e​f​i​n​g​-​E​-​B​i​k​e​s​-​e​n​g.pdf
2D’après une mise à jour en novem­bre 2023 des don­nées : https://​doi​.org/​1​0​.​1​0​1​6​/​j​.​t​r​d​.​2​0​2​1​.​1​02743
3Site inter­net con­sulté le 24/11/2023 : https://​alucy​cle​.world​-alu​mini​um​.org/​p​u​b​l​i​c​/​g​l​o​b​a​l​/​i​n​d​e​x​.html

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