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2 October 2019

Going beyond Well-to-Wheel: Life Cycle Emissions

Well-to-Wheel emissions are also called “in-use” emissions as they are proportional to the fuel or energy consumption of the vehicle.

With a Life Cycle Assessment – LCA – we normally intend a more complete evaluation of the emissions associated not only to the use of the vehicle, but also to its manufacturing process and to the so called ‘end of life’ (vehicle dismantling and material recycling). In other words: LCA is a technique that provides an emissions estimation over the entire lifetime of a vehicle.

According to ACEA statistics, the average lifetime of a passenger car in the EU is 10,5 years. This is with an average mileage of 15 000 km, resulting in an overall mileage of 160 000 km.

Why is it important to measure vehicle emissions with an LCA and what can we learn from it?

As long as the transport system was based on conventional technologies, based on Internal Combustion Engine – ICE – configurations, the manufacturing and end of life processes were quite similar. Diesel powertrains have a slight wider impact due to a major complexity of their gas aftertreatment system.

In the current scenario, with a progressive penetration of electrified architectures, the LCA approach is very important as today, battery manufacturing is still critical considering to two aspects:

  • the energy intensity and CO2 emissions from the manufacturing process
  • the recycling of batteries, particularly important due to the scarcity of materials like Lithium, Cobalt and Nickel

In a recent study published by IVL Swedish Environmental Research Institute, the most likely range of CO2 footprint of the Lithium-ion batteries manufacturing process is indicated and based on a wide literature review:

This table tells us that a vehicle equipped with a 50 kWh battery pack, assuming an average value of 90 kg CO2/kWh from the table above, has a 4 500 kg CO2 footprint from the manufacturing of the battery pack alone.

Is this a significant amount of CO2?

Let’s run a comparison of the GHG emissions considering all the steps as indicated in the figure below:

When looking at a C-segment vehicle, which is representative of the EU market today, we can expect the following tailpipe (TTW) emissions:

  • Petrol: 115 g/km
  • Diesel: 102 g/km
  • Petrol HEV: 85 g/km
  • Petrol PHEV: 40 g/km
  • CNG: 94 g/km

For a BEV (Battery Electric Vehicle) we have considered an energy consumption of 14,5 kWh/100 km, with a current EU energy mix of 106 g CO2/MJ and a forecast of 72 g CO2/MJ in 2030.

The figure below shows us that when moving from tailpipe emissions to a Well-to-Wheel (WtW), and then to the LCA measuring approach, we can realize that carbon neutrality could be achieved not only with full electric solutions but also with other alternatives. Anyway, thanks to the higher powertrain efficiency, BEVs provide better performance than the other solutions fuelled with fossil fuels.

How does the use of renewable gas affect vehicle performance?

The following graph illustrates how the overall LCA results change when considering the options coming from renewable gas, and as well as from the use of renewable electricity.

The graph shows that renewable gas drastically reduces the LCA footprint from natural gas technologies, thanks to the contribution from Well-to-Tank (WTT) emissions that result negative.

Of course, this is also considering an electricity supply fully based on solar/wind with which we can achieve very interesting results, also reducing drastically the WTT contribution (but not becoming negative as with renewable gas).

The following figure provides the overall result as LCA footprint from all different technologies considered:

Some considerations following the graph:

  • CNG (fossil) emissions are equivalent to those from gasoline HEV and PHEV
  • Feeding a CNG vehicle with biomethane produced from municipal waste and/or with synthetic gas, leads to the same low amount of emissions as a BEV under the assumption that wind/solar electricity is used
  • Using biomethane from liquid manure is a very pragmatic and effective way to generate negative carbon emissions! This means that, when running a CNG vehicle, its use would contribute to capturing CO2 from the atmosphere.

Similar conclusions are also reported in a recently published study published by IFPEN and also the ADAC which is an automobile association in Germany.

How to use this kind of analysis?

An LCA footprint represents an interesting, yet essential indicator to assess the total CO2 emissions associated with a certain vehicle technology. When considering our target to decarbonize the transport system, this is the right angle to approach the needed analysis. In fact, GHG emissions need to be considered at global scale and as the result of a sum of contributions. Zero tailpipe emissions are important for the air quality in our cities ⁠— but overall GHG emissions have a different, and much bigger dimension.

Concerning natural gas, thanks to the shown graphs it became clear that today’s solutions based on conventional technologies have a better manufacturing footprint than newer solutions. When considering the use of renewable gas, no matter its origin, the overall footprint of a NGV is very competitive.

This is not about questioning electric mobility in general, but it is key to understand that there exist already other solutions that can contribute to a fast acceleration of the decarbonisation process in transport — for example NGVs:

Transforming waste biomass into clean fuel or capturing CO2 emissions and transforming these into synthetic methane and combining them within highly efficient dedicated natural gas engines is already possible today.

And even more, combining these in the future also with mild-hybrid and other electrified architectures will enable an additional step towards an integrated approach to fully accelerate energy efficiency and shift to a fully carbon neutral direction — thanks to gas in transport!


Find the related article 'The European Green Deal: time to start!' here, and 'CO2 emissions and carbon neutrality' here

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