More nuclear, battery and gas-powered vessels are needed to cut shipping emissions in the absence of a single magic bullet solution, according to a new report.
Diesel engines are likely to remain the most common form of shipping propulsion in the short term but converting ships to use liquid natural gas (LNG) would provide a cheaper, cleaner and well understood alternative, said the study from the Royal Academy of Engineering.
In the medium-to-long term, the shipping industry needs to adapt current technologies and develop new ones that use fuel cells, batteries and nuclear reactors, augmented by renewable power sources such as wind and solar, the report concluded.
Prof John Carlton of City University London, who led the working party that surveyed the propulsion options available shipping, said there was no single winning technology and different solutions would be needed for different vessels.
‘We know that larger ships are more carbon-efficient than smaller ships and that slower ship speeds effectively reduce emissions,’ he said in a statement. ‘But fitting smaller engines in large ships may increase the risk of being under-powered in bad weather.’
Alongside LNG, which requires the development of a global infrastructure, gas turbines were described as a potential short-term solution that has been successfully used in niche areas of the marine market but faced the issues of expensive fuel and lower efficiencies than existing slower-speed diesel engines.
In the medium term, biofuels, particularly those made from algae or other micoorganisms, are seen as an alternative but further work is needed on their storage, handling, and impacts on health, safety and the environment.
Fuel cells are another option, with high-temperature solid oxide and molten carbonate models showing the most promise for propulsion, the report says, and low-temperature proton exchange membrane fuel cells for lower power generation.
Nuclear ship propulsion produces no emissions and there is a significant body of experience of its use, but conventional methods of design, manufacture and operation would need a complete overhaul for commercial use, and issues of regulation and public perception would need to be addressed. It also requires high capital investment and a new global infrastructure support system.
Battery technology is developing rapidly and produces no emissions, the report said. ‘However, full ship battery propulsion requires further technical development and is likely to be confined to relatively small ships.’
On the other hand, the report pointed to batteries’ potential in hybrid solutions for some small- to medium-sized ships, providing recharging doesn’t increase overall emissions from land-based energy generation.
‘Hydrogen, compressed air and liquid nitrogen are likely to be long-term propulsion considerations,’ the report said. But all three require land-based sources of power for creation and distribution infrastructure.
Royal Academy of Engineering president Sir John Parker said: ‘As for all industries, concerns about climate change require the reduction of greenhouse gas emissions from the shipping sector.
‘This entails higher fuel prices for low sulphur fuels. It means that the industry must prepare for the new future and investigate alternative, more economic ship propulsion systems.’