What are the Sustainable Fuel Alternatives for Logistics Operations?

Logistics includes such activities as road, rail, sea and air transport, as well as warehousing and terminal operations. These involve the use of large amounts of fuel and account for an estimated 10 to 20 per cent of global greenhouse gas emissions. There is, therefore, a great deal of interest in finding appropriate sustainable fuels to replace the fossil fuels that are currently used in the vast majority of these activities.

Road freight

Road is the main transport mode used and is therefore regarded as the largest emitter of logistics greenhouse gases. Diesel is the principal fuel, although there are a number of other fossil fuels that can be used that have some environmental benefits, including liquefied petroleum gas (LPG), compressed natural gas (CNG), and liquefied natural gas (LNG).

Biofuels are a potentially sustainable alternative to fossil fuels. They are seen as sustainable as the carbon dioxide emitted in use is at least partly compensated by the absorption of carbon dioxide by the growing of the new crops. However, there are concerns about the loss of land for growing food where the ground is already used for agriculture, and about the release of carbon gases sequestered in the soil where there is a change of land use from pristine landscape (and almost certainly an associated reduction in biodiversity). A prominent form of biofuel is biodiesel, which is normally a mix of diesel and refined vegetable oils from plants such as soybean, palm, and rapeseed. A mix with fossil fuels containing 5 to 20% of biofuel is fairly common. A similar option is the use of bioethanol which is produced by the fermentation of crops such as sugarcane or corn. A further alternative is biomethane which is produced by the anaerobic digestion of organic matter. The latter may be from agricultural crops but is often from waste material such as sewage, farm waste, food waste and landfill sites. In this way, the methane is burnt when used rather than escaping from waste sites as methane gas which is, in fact, much more potent in terms of global warming than carbon dioxide.

Synthetic fuels are produced by a chemical process, normally from coal, gas, or organic matter. Issues around their use and environmental credentials are similar in many ways to biofuels and thus the source of the feedstocks is important (e.g. agricultural crops or waste cooking oil). Hydrotreated vegetable oil (HVO) is one such fuel and is manufactured by saturating feedstocks at high temperatures and then ‘cracking’ to remove impurities. This process thus avoids some of the harmful emissions associated with conventional diesel. Another option is the use of dimethyl ether (DME), which is produced from coal, natural gas, black liquor (a by-product of paper pulp manufacturing), or biomass. It can be substituted for diesel or LPG or as a hydrogen-rich source for fuel cells.

Lithium-ion batteries now offer a popular option, particularly for light commercial vehicles. The use of batteries avoids the emission of carbon dioxide and harmful particulates from vehicles, but their environmental credentials largely depend on the source of electricity. If the electricity is produced from renewable sources (e.g. wind or solar) they can be regarded as extremely ‘green’.

A further option is the use of hydrogen fuel cells which produce electricity to drive a vehicle by means of a chemical reaction. Hydrogen is supplied to the cathode and oxygen to the anode in the cell, with the resulting reaction forming an electric current, plus water as the by-product. There are no other tail-pipe emissions. However, power is required to produce hydrogen and currently, there are two main options that could be regarded as having a limited impact on global warming. One is ‘green’ hydrogen produced by electrolysis using electricity from renewable sources, and the other is ‘blue’ hydrogen which is produced from natural gas with the resultant carbon being captured and stored (e.g. underground). Owing to their relatively high energy density, hydrogen fuel cells are regarded as a serious contender for powering heavy goods vehicles.

Another possible option for heavy goods vehicles is that of electric road systems (ERS). These overcome the energy loss involved in the hydrogen conversion processes by providing electricity directly to vehicles by means of overhead catenary wires – in the same way as overhead electric wires for rail traction and trolleybuses. Owing to the infrastructure costs, this type of system may be limited to the main road networks with other technologies (e.g. battery or hydrogen fuel cells) being used for the shorter legs of the journey.

Rail freight

As with road transport, diesel is the main fuel used for freight locomotives in most countries. There are also some instances of compressed natural gas (another fossil fuel discussed above) being used.

In some parts of the world, electric freight locomotives can pick up electricity directly from overhead catenary wires, with the sustainability of this option being dependent on the source of the grid electricity (i.e. wind, solar, coal, gas, etc). Such rail electrification requires considerable investment and is therefore often only available on the main routes. With rail freight, it is possible to change locomotives so that other parts of the journey can be undertaken using different fuels.

Similar sustainable technologies to road are being used or trialled for rail freight, notably hydrotreated vegetable oil (HVO), lithium-ion batteries and hydrogen fuel cells.

Maritime freight

Most ships use heavy fuel oil for propulsion, producing greenhouse gases as well as other pollutants, such as sulphur. A major recent international initiative has concentrated on reducing this latter pollutant and since 2020 there has been a cap on the percentage of sulphur that can be emitted. This has resulted in ships either being fitted with scrubbers to remove sulphur from the exhaust or using very low sulphur fuel oil (VLSFO). Other fossil fuels such as liquefied natural gas and methanol (produced from natural gas) are alternatives that have some environmental advantages.

Potential non-fossil fuels include ‘green methanol’ (produced from waste or biomass, together with ‘green’ hydrogen), alcohol-lignin blends (methanol or ethanol blended with lignin, found in the cell walls of many plants and trees), ‘green ammonia’ (from nitrogen and hydrogen produced with renewable energy) and biofuels. A further alternative is nuclear power as currently used for large aircraft carriers, submarines, and icebreakers.

Electric power using lithium-ion batteries can be used for short-sea shipping, as well as by larger ships for approaching ports and for port manoeuvring. Hydrogen cells can also be used for similar purposes. Power assistance to the main engines may be provided using wind, such as rotor sails that consist of vertically rotating drums, or solar panels.

In port, shore power provision by electric plug-in points can enable ships’ engines to be turned off whilst providing for lighting, heating, refrigeration, etc.

Air freight

Air freight presents a particular challenge owing to the operating environment and the weight constraints imposed by the need to take off and fly. There has been much interest in sustainable aviation fuel (SAF) which is generally a blend of conventional fossil-based aviation fuel and fuel produced from household, industrial and agricultural waste. It can be used directly in existing airport fuelling infrastructure and aircraft engines.

Another alternative that is currently being used is electric battery power, but current technology only allows a power-to-weight ratio suitable for smaller aeroplanes and/or short distances. There is therefore much attention now on further alternatives such as the use of hydrogen which could be used in hydrogen fuel cells, for hydrogen combustion in modified gas turbine engines, or as synthetic hydrogen fuel produced from renewable sources.

Warehouses and logistics terminals

For warehouse trucks, the options are similar to road freight. The main fossil-fuel options to diesel are liquefied petroleum gas (LPG) and compressed natural gas (CNG). However, for indoor use, lead-acid batteries have been extremely common for many years and more recent alternatives include lithium-ion batteries and hydrogen fuel cells, both described earlier.

Conclusion

There is, therefore, a wide range of alternative sustainable fuels being developed, or in use, for logistics operations. However, it is clear that there are no easy answers as each fuel type is associated with significant environmental challenges.

Biofuels can lead to the release of carbon dioxide sequestered in pristine soil and trees, a decrease in biodiversity and/or a loss of land for food crops. Synthetic fuels can face similar challenges depending on the feedstocks used. When they are produced from waste products, it raises the question of whether there is enough waste for the production to be scaled up sufficiently. The environmental benefits of hydrogen depend largely on how the gas is produced, but a further factor is the loss of energy in the two-stage conversion process – from electricity to hydrogen fuel cells and then back to electricity. The various electric options appear attractive if the generation of electricity from renewable sources can be scaled up globally to produce sufficient energy for the entire national grid networks. When nuclear power is used, there are always environmental concerns regarding potential radioactive leaks and the disposal of waste, particularly concerning the lengthy ‘half-lives’ (i.e. decay rates) of radioactive substances. Even when electricity can be produced from wholly sustainable sources, then the infrastructure, batteries and other components often contain considerable ‘embodied carbon’ (i.e. carbon dioxide produced in their manufacture); as well as raising the issue of whether the extraction of materials, such as lithium and cobalt, can be undertaken in an environmentally friendly and ethical way. It will be very interesting to see how these challenges will be overcome and which fuels will become dominant in each of the transport and storage sectors discussed above.

There are of course many other aspects of sustainability in logistics, such as the overarching international agreements, governmental actions and company environmental management systems (EMS). These, as well as the sustainable transport fuels discussed above and other specific areas (e.g. heating and lighting for warehouses), are all covered in The Handbook of Logistics and Distribution Management (7th Edition).