Decarbonising ships, planes and trucks: An analysis of suitable low-carbon fuels for the maritime, aviation and haulage sectors

The high environmental impacts of transport mean that there is an increasing interest in utilising low-carbon alternative energy carriers and powertrains within the sector. While electricity has been mooted as the energy carrier of choice for passenger vehicles, as the mass and range of the vehicle increases, electrification becomes more difficult. This paper reviews the shipping, aviation and haulage sectors, and a range of low-carbon energy carriers (electricity, biofuels, hydrogen, and electrofuels) that can be used to decarbonise them. Energy carriers were assessed based on their energy density, specific energy, cost, lifecycle greenhouse gas emissions, and land-use. In terms of haulage, current battery electric vehicles may be technically feasible, however the specific energy of current battery technology reduces the payload capacity and range when compared to diesel. To alleviate these issues, biomethane represents a mature technology with potential co-benefits, while hydrogen is close to competitiveness but requires significant infrastructure. Energy density issues preclude the use of batteries in shipping which requires energy dense liquids or compressed gaseous fuels that allow for retrofits/current hull designs, with methanol being particularly appropriate here. Future shipping may be achieved with ammonia or hydrogen, but hull design will need to be changed significantly. Regulations and aircraft design mean that commercial aviation is dependant on drop-in jet fuels for the foreseeable future, with power-to-liquid fuels being deemed the most suitable option due to the scales required. Fuel costs and a lack of refuelling infrastructure were identified as key barriers facing the uptake of alternatives, with policy and financial incentives required to encourage the uptake of low-carbon fuels.