Maritime Cleantech – Commercial Shipping
Goods and people have been transported by sea throughout human history. In the modern world, shipping remains the most efficient method for moving cargo where speed is not a major concern. Large quantities of material can be moved using relatively little fuel compared to alternatives such as road haulage, trains, and aeroplanes. Shipping makes up approximately 80% of the EU’s imports and exports by volume, and the International Chamber of Shipping estimates that 1.5 tons of cargo per person per year are carried by sea worldwide.
Commercial shipping is almost entirely powered by fossil fuels. As a consequence, maritime traffic is estimated to produce approximately 3% of global carbon emissions. Significant work is therefore being focussed on technologies that can reduce emissions from the maritime sector as part of wider efforts to decarbonise the world economy.
For much of human history, ships have been propelled by the wind using sails. Steam and internal combustion engines finally displaced sail for commercial shipping in the 20th century due to their greater reliability. However, wind-powered ships may be making a comeback.
The Flettner rotor, also known as a rotor sail, is a tall cylinder with a flat end cap fixed upright onto a ship’s deck, appearing much like a funnel. The cylinder is spun around its long axis by an onboard power supply. Wind blowing past the rotating cylinder produces a force on the rotor perpendicular to the wind direction due to the Magnus effect. This force can be harnessed to help propel the ship.
A Flettner rotor still requires an onboard power supply to spin the rotor, but fuel efficiency can be greatly increased by reducing load on the ship’s engines. In addition, the rotors can be retrofitted to existing ships, avoiding the cost associated with replacing a ship entirely.
Current batteries store much less energy per unit volume compared to fossil fuels and take longer to recharge than refuelling a fossil-fuel vehicle. The increased downtime and reduced range mean that current battery-electric vehicles cannot compete with fossil fuels for long-distance commercial applications such as road haulage, railways, and shipping.
However, battery-electric ships may still be suitable for short-range travel or applications where ships are expected to have relatively high downtime that could be used for recharging. A prototype electric boat has already been tested in Belfast port as a workboat for transporting pilots and crew to and from larger ships in the port. It is hoped that similar boats could be used for short-range ferry routes around the UK.
Just like other transport sectors, development in clean maritime is also being focussed on engines that can run on alternative fuels. A variety of different technologies are being investigated including biofuels, hydrogen combustion, and hydrogen fuel cells.
Ammonia has also been considered as a fuel source for shipping. Similar to hydrogen, ammonia can be used in either an internal combustion engine or in a fuel cell to drive an electric motor. However, ammonia has a higher energy density than hydrogen and can more easily be stored and transported in liquid form due to its higher boiling point. This has advantages compared to hydrogen for shipping, where range is a significant concern. In addition, ammonia is already used as a fertilizer worldwide. This means that infrastructure for storing and transporting ammonia already exists in many ports around the world.
Despite these advantages, ammonia-fuelled shipping will only produce carbon reductions if the ammonia itself is generated using renewable energy, just as for other alternative fuels. The vast majority of ammonia is currently produced from natural gas using the highly energy-intensive Haber process, and so changes to the supply chain will be needed as well for decarbonisation.
The international nature of much global shipping creates additional difficulties with decarbonisation. Many novel shipping technologies such as alternative fuels require new infrastructure such as electric charging points or depots to store alternative fuels. It is no use leaving your home port on a hydrogen-powered ship if there is not guaranteed to be hydrogen for refuelling at your destination port.
To facilitate uptake of cleaner maritime technologies, a number of countries have started initiatives to form so-called “green corridors”. These are specific shipping routes along which the countries commit to promote the implementation of the supporting infrastructure for low-carbon shipping technologies. At COP26 in November 2021, 24 countries signed the Clydebank declaration committing to establishing green corridors between their ports.
Shipping is an important sector that still has a long way to go in terms of decarbonisation. An additional difficulty is that many ships are registered in small jurisdictions with relatively little regulation. This may make it more difficult to promote uptake of green technologies. Encouragingly, the International Maritime Organisation, a branch of the UN whose members include most countries in the world, recently agreed unanimously to achieve net zero shipping by or around 2050.
The exact pathway to this goal remains unclear, but nonetheless the agreement represents an important step. Research and development in the sector are only likely to accelerate in the coming years as efforts to decarbonise the world economy intensify.