Solutions
There is now a range of alternative energy systems available for shipping and aviation, but which are
the most sustainable?
Decarbonising shipping and aviation
Most shipping and aviation is currently powered by fossil fuels, heavy fuel oil for ships and kerosene in planes. Unlike sectors like road transport, household heating or power generation, long-haul shipping and aviation is not easy to electrify – but it is not impossible.
Battery-electric solutions for short air and sea journeys are being developed, while synthetic fuels – or “e-fuels” – where all the inputs are derived from renewable electricity can decarbonise long-haul voyages.
The SASHA Coalition advocates for policy that supports solutions that:
Have the potential to reduce the most greenhouse gas emissions;
Are scalable;
Do not lead to fossil fuel lock-in.
The most sustainable solutions
Zero carbon emission ships and planes
As is the case across all sectors, the most sustainable energy system is one that directly uses electricity that has been generated from renewable sources.
Today, only small planes and marine vessels can be powered by electrical propulsion systems. Larger craft can also be powered by hydrogen converted to electricity in a fuel cell. If the hydrogen is produced via water electrolysis using renewable energy then these will also have near zero associated carbon emissions across their lifecycle.
To reach commercial scale, policies need to be put in place that incentivise their uptake and the rollout of necessary refuelling and charging infrastructure.
Read our briefing on accelerating zero carbon emission flight.
E-fuels
For long-haul journeys, the most sustainable alternative to fossil fuels is e-fuels.
For shipping, there are two main marine e-fuels: e-ammonia and e-methanol. These can both be near zero-emission fuels if produced sustainably.
E-ammonia does not release CO2 emissions when burnt. If the hydrogen it contains is produced using renewable electricity, then e-ammonia releases only very few carbon emissions across its lifecycle.
However, other environmentally harmful gases may be emitted across the ammonia supply chain, including nitrous oxide, nitrogen oxides, hydrogen, and even ammonia itself. Stringent regulations will be vital to minimise these negative effects. Using e-ammonia at scale will also require new infrastructure and engines on ships.
E-methanol does release CO2 emissions when burnt, but if the carbon it is produced with comes from a sustainable source then it will have near net zero carbon emissions across its lifecycle. Methanol is largely compatible with existing infrastructure, and is being used already on some ships whose engines have been modified to accommodate it.
For aviation, e-kerosene is the most sustainable drop-in fuel, produced with sustainably-sourced carbon and renewable hydrogen. While it has near net zero carbon emissions, it still produces negatively impactful non-CO2 emissions.
Given e-fuels are more expensive than fossil fuels, policy is needed to narrow the price gap between them and conventional fuels, and to fund innovation to see costs reduce.
Our members and knowledge partners
E-fuels
Zero carbon emission technologies
Less sustainable technologies
Zero carbon emission technologies and e-fuels are the most sustainable solutions but have to compete for support against alternatives that are more technologically advanced and less sustainable. The SASHA Coalition does not advocate for policy to support these technologies.
Biofuels
Biofuels are made from biomass, and have a wide range of environmental impacts depending on where the material they are produced from.
The most easily accessible kind of biofuels are produced using crops that would otherwise be eaten. These have high associated carbon emissions from land use change (in some cases more than from fossil fuels), and dire consequences for biodiversity and food systems.
Advanced biofuels are produced with waste products such as used oils or agricultural waste. While these may have significantly lower carbon emissions compared to fossil fuels, truly sustainable feedstocks are severely limited in supply, meaning they are not a reliable energy source for decarbonising shipping and aviation.
Read our report on the biodiversity impacts of biofuels.
Fossil liquified natural gas (LNG)
Fossil LNG has been touted as a sustainable “transition” fuel – but it is itself a fossil fuel. While LNG does produce less carbon dioxide at the point of combustion, it consists mainly of methane, which is a greenhouse gas around 30 times more potent than carbon dioxide over a 100-year period. Methane is prone to slip or leak across the LNG lifecycle.
For this reason, even e-LNG, an e-fuel produced using renewable hydrogen, still causes huge climate damage even if it is produced using a renewable source of carbon. E-LNG also contributes to LNG lock-in, since it would involve investment into LNG infrastructure that will ultimately slow the transition away from fossil LNG and prolong its use.
Read Opportunity Green’s report on the use of LNG as a shipping fuel.