Executive summary
Sustainable fuels play a crucial role in clean energy
transitions
Sustainable fuels complement direct electrification and energy efficiency
measures in decarbonising sectors for which emissions are hard to abate.
Under the IEA’s Net Zero Emissions by 2050 (NZE) Scenario, the demand for lowemission fuels such as liquid biofuels, biogases, hydrogen and hydrogen-based
fuels would need to double from current levels by 2030 and double again by 2050.
They facilitate decarbonisation across a range of end-use sectors, especially parts
of transport and industry, while contributing to energy diversification and security.
None of the main sustainable fuel options are on track for a net zero pathway.
There are potentially hundreds of pathways available for producing fuels. Biofuels
are currently the most developed and cost-effective alternative to fossil fuels.
However, substantial efforts are needed to expand and diversify sustainable
biomass feedstock supplies, commercialise new processing technologies and
harmonise sustainability frameworks to address concerns related to large-scale
deployment. Hydrogen has significant industrial demand today, but supply of lowemission hydrogen is very limited so far. In addition to scaling up low-emission
production and reducing cost, significant investments in distribution infrastructure
and end-use equipment are needed. Hydrogen-based low-emission fuels typically
offer some benefits in terms of lower infrastructure requirements compared to pure
hydrogen, but they are more expensive to produce, and their scale-up is further
limited by access to low-cost, low-emission sources of CO₂ feedstock (except for
ammonia which is carbon-free).

Examples of production pathways and technologies for sustainable fuels
and potential synergies

System boundary for fuel supply chains
With the emergence of regulations and certification systems for sustainable fuels,
the ability to calculate the GHG intensity for fuels in a transparent and comparable
way has become important. Any robust calculation a fuel’s GHG intensity (usually
expressed as grams of CO2 equivalent per megajoule of fuel, or gCO2-eq/MJ) starts
with the definition of a system boundary that describes all elements in the fuel
supply chain that are considered relevant for the assessment.

System boundary for comparing the supply chain GHG intensity of fuels

Emissions from construction and manufacturing of assets (usually called embodied
emissions, or capital goods emissions) are usually excluded from the lifecycle
assessment, as they are deemed to be low and therefore below the typical cut-off
criteria. However, in the case of fuels produced via electrolysis, GHG emissions
from the manufacture of captive power plants (e.g. renewable or nuclear) should be
included within the system boundary, as their contribution may be non-negligible.

Source:https://www.iea.org/reports/towards-common-criteria-for-sustainable-fuels