Well-to-Wheel (WTW)

Introduction

The term “well-to-wheel” (WTW) is a standard approach for assessing the climate impact of vehicles and powertrains. It encompasses not only emissions generated during vehicle operation but also accounts for upstream emissions resulting from the extraction, processing, and supply of energy sources. In this way, WTW complements traditional tank-to-wheel analyses, which consider only the use phase.

The Importance of the Well-to-Wheel Approach

When it comes to climate management in the transition to sustainable transportation, it is not enough to focus solely on emissions during vehicle operation. Electricity for electric vehicles, hydrogen, synthetic fuels, and fossil fuels all generate significant emissions throughout their supply chains.

WTW therefore combines two levels:

1. Well-to-Tank (WTT) – Emissions associated with the extraction, production, transport, and storage of the energy source.
2. Tank-to-Wheel (TTW) – Emissions during vehicle operation.
   

This combination provides a comprehensive picture of a powertrain’s carbon footprint.

Relevance for Business and Politics

For companies in the automotive, logistics, and energy sectors, the WTW approach is essential for transparently presenting the actual climate impact of their products and services. The well-to-wheel approach is becoming increasingly relevant, particularly in the context of Scope 3 accounting (especially categories such as 3.1 “Purchased Goods and Services” or 3.11 “Use of Sold Products”) according to the GHG Protocol.

Policymakers are also using WTW assessments to better guide regulations and incentive programs. For example, an analysis by Agora Verkehrswende shows that the climate benefits of electric vehicles are only fully apparent in a WTW comparison—especially as the share of renewable energy in the electricity mix increases.

Use Cases and Examples

The well-to-wheel approach is particularly relevant when evaluating the actual climate impact of different propulsion technologies. While battery-electric vehicles produce no local emissions at the well-to-wheel level, their well-to-well balance depends heavily on the electricity mix and the emissions from battery production. In contrast, internal combustion engine vehicles powered by fossil fuels generate significant emissions both during operation and in the upstream supply chain.

Typical use cases include:

• Comparison of different powertrains: electric cars vs. internal combustion engines vs. hydrogen vehicles – taking into account operation and energy supply.
• Strategic Decision-Making: WTW provides fleet managers and OEMs with the foundation for investing in new technologies.
• Climate policies: EU targets and national emissions budgets are based on life-cycle assessments, as this is the only way to realistically reflect their climate impact.
• Communication with stakeholders: Investors, customers, and the public expect transparent, clear statements regarding the company’s carbon footprint.
  

Here’s a concrete example: An electric vehicle produces no local emissions. However, in a life-cycle assessment, emissions can vary significantly depending on the electricity mix and the upstream emissions from battery production.

Challenges and Limitations

WTW accounting is methodologically complex. It requires comprehensive data and consistent valuation methods. In practice, several key challenges arise:

• Heterogeneous data sources: The electricity mix, the origin of hydrogen, and the production methods for biofuels vary significantly depending on the region and technology.
• Methodological differences: Differing assumptions regarding battery life, charging losses, or drive efficiency often lead to different results.
• Dynamic developments: As the share of renewable energy increases, the life-cycle assessments of electric vehicles automatically improve—while fossil-fuel-powered vehicles lag behind in comparison.
  

To ensure that results remain comparable, clear standards and consistent data sources are necessary. Without them, there is a risk of misinterpretations or inconsistent reports.

Integration with Standards & Reporting

The WTW approach is closely integrated with existing standards and reporting requirements. It thus serves as a bridge between technical analysis and regulatory obligations:

• GHG Protocol: This approach is implicitly reflected in the Scope 3 categories, particularly in energy use and the use of sold products.
• ISO 14040/44: Provide the methodological basis for life cycle assessments (LCA), into which WTW analyses can be integrated as a component.
• CSRD / ESRS: Companies in the transportation or mobility sectors must disclose their climate impact across the entire value chain—making WTW an indispensable component of sustainability reporting.

Practical Tips

Companies that wish to incorporate WTW analyses into their climate strategy should:

• rely on transparent data sources and clearly document the methodology,
• update regularly, as energy mixes change dynamically,
• Clearly communicate results to avoid misunderstandings (e.g., the difference between TTW and WTW).

Further reading

• Environmental Database: Well-to-Wheel
• Agora Verkehrswende: Carbon Footprint of Battery-Powered and Alternative Drivetrains (PDF)
• GHG Protocol – Scope 3 Draft 2024