Calculating our CO₂ savings

Back in April 2020, we launched our CO₂ counter in the cars - so you can keep track of your personal CO₂ savings on the taximeter during your Viggo trip.

At the time, we made a blog post about our CO₂ calculations - you can find it here. In the post you’ll also find explanations of the difference between CO₂ and CO₂ equivalents, as well as the reason behind our firm belief in the electric car being a large part of our future in mobility.

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Since we published the latest calculations, new knowledge and new figures have been published about Denmark's electricity mix in 2019. These new figures naturally have an impact on the CO₂ savings we have calculated.

The Danish electricity mix in 2018 emitted 212 g CO₂ / kWh. In 2019, the number was further lowered to just 135 g CO₂ / kWh.

In conclusion, this prompted us to review our calculations, and below is a brief review of the method used as well as our sources.

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Comparison of a diesel car with an electric car - the Life Cycle Analysis

Every car production has a CO₂ footprint - both in the form of materials used, but also in the form of the electricity used to produce the individual car. On top of this comes the use - of either electricity for the battery or fossil fuels for the internal combustion engine.

By taking the total emissions from both production and use and dividing this by the number of km driven over a car's "lifetime", you can find the CO₂ that is emitted per km.

We have used a so-called Life Cycle Analysis (LCA) to calculate CO₂ emissions per km driven in the two different cars. The calculation looks like this:

CO₂-emissions per km = (emissions from production + emissions from driving) / amount of km driven

Emissions from production = battery+car production + car maintenance

Emissions from driving = energy use in kWh per km * CO₂-emissions per kWh

Apart from these simple formulae, below is a further explanation of the various terms:

Diesel car

• Car production
  Covers all the emissions from producing the different parts of the car
  
• Upstream emissions
  Covers the emissions related to sending out fossil fuels to the gas (petrol) station
  
• Tank-to-wheel
  Covers the emissions from the fuel used in the car for driving
  

Electric car

• Car production
  Covers the emissions from the entire car production except the battery
  
• Battery production
  The CO₂ emissions from producing the battery
  
• Upstream emissions
  The CO₂ emissions related to transmitting the energy to the charging station
  
• Tank-to-wheel
  Covers the emissions from the energy used in the car. These emissions depend on the Danish “electricity mix”. The term electricity mix covers how much of our electricity originates from renewable sources (such as sun and wind), and how much originates from fossil fuels.
  

Assumptions

The basic assumptions of any calculation is important for the outcome - and below is a list of ours:

• Choice of car
  We have chosen to compare a Tesla Model 3 Long Range with a smaller diesel car often used as a taxi, Mercedes-Benz C220D. Both models are used regularly as taxis but in order to be on the more conservative side with our calculations, we have chosen a diesel car which is slightly smaller than the Tesla Model 3.
  
• Lifecycle
  A taxi drives a lot of kilometers during its lifespan. We have made a relatively conservative estimate and based our calculations on 300.000 kilometers.
  
• The Danish electricity mix
  The Danish electricity mix depends on how much of our electricity comes from renewable sources such as solar and wind, and how much is extracted from fossil fuels. The Danish electricity mix was more sustainable in 2019 than in 2018, which resulted in emissions of 135 g CO₂/kWh.

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Our sources for calculating CO₂ emissions by the various cars

To avoid "cherry-picking" our data, we have consulted figures from three different studies:

1. Ellington et al, The International Council for Clean Transportation og Mercedes
   For the electric car, we have made a calculation based on the peer-reviewed study Ellington et al, as well as an analysis made by The International Council for Clean Transportation (ICCT). The Ellington et al analysis has also been used in the calculations for the diesel car, where we have also taken the official figures from Mercedes.
   
2. Luxembourg Institute of Science and Technology (LIST)
   LIST has made a calculator explaining how much CO₂ is emitted by different car types. They have also based their figures on the analysis made by The International Council for Clean Transportation (ICCT) and the numbers have then been adjusted with forskning.no’s calculator for reducing the range of batteries in winter times (if you try the calculator, remember to edit the CO₂ emissions from the electricity mix, as their default is European numbers and not Danish).
   
3. Carbonbrief
   Carbonbrief has in part also used ICCT, but has then added battery calculations from IVL Swedish Environmental Institute.

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The Ellington et al calculation

Below you can see the calculation made from the numbers drawn from Ellington et al:

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The difference per km driven is therefore 175-79 = 96 g CO₂ equivalents per km.

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The LIST calculation

Below you can see the calculation made by LIST, available on their calculator:

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The difference per km driven is therefore 192-71 = 121 g CO₂ equivalents per km.

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The Carbonbrief calculation

Below you can see the calculation made from the numbers drawn from Carbonbrief and edited with our assumptions:

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The difference per km driven is therefore 175-83 = 92 g CO₂ equivalents per km.

Conclusion

According to our calculations based on data from the three sources, you save somewhere between 92 and 121 g CO₂ equivalents per km driven by choosing a Tesla Model 3 versus a Mercedes-Benz C220D.

The average of the three is 103 g CO₂ / km.

Therefore, the official savings we count is 103 g CO₂ / km.

As a side note, this calculation only includes the climate footprint. Aside from this, with tailpipe emissions from diesel cars, there is also a high level of air pollution, which affects our quality of life in cities - and this is an added value of the electric car.

If you have any questions regarding these calculations, you are of course always welcome to contact us.

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