Lifecycle emissions of synthetic e-fuels
Lifecycle emissions measure total greenhouse gases from fuel production through combustion. For e-fuels, the dominant factors are the carbon intensity of the electricity used to make hydrogen and capture CO2.
Main lifecycle components
- Electricity for electrolysis: the largest contributor; if renewables power electrolysis, emissions are low.
- CO2 source: using fossil-derived CO2 without capture or proper accounting undermines benefits. CO2 from direct air capture or industrial waste streams paired with renewables provides a lower lifecycle footprint.
- Conversion and processing: synthesis and refining steps consume energy, adding to emissions if not powered by clean energy.
- Combustion: when e-fuels are burned, the carbon is released, so lifecycle benefits rely on the CO2 being captured initially from a non-fossil source or balanced by removals.
Typical outcomes
- With fully renewable electricity and sustainable CO2 sources, e-fuels can approach near-zero lifecycle emissions, effectively recycling carbon.
- If grid electricity contains fossil generation or CO2 sources are fossil without net removals, lifecycle emissions may be similar to or worse than fossil fuels.
Comparisons and trade-offs
- Versus batteries: batteries have lower lifecycle losses for ground transport because electricity goes directly to the motor, avoiding conversion losses inherent in e-fuels.
- Versus biofuels: biofuels can be low-carbon but compete for land; e-fuels avoid land use but need more electricity.
Best practices to minimize emissions
- Use dedicated renewable electricity or contracts guaranteeing low-carbon power.
- Source CO2 from DAC or sustainably managed industrial sources.
- Improve process efficiencies and integrate waste heat recovery.
Conclusion
E-fuels can deliver low lifecycle emissions if produced with clean electricity and appropriate CO2 sources. The environmental benefit depends critically on the supply chain and energy inputs.