Alternative fuels are essentially free of sulphur and thus help with compliance with environmental regulations, as well as the potential for a smaller carbon footprint.
One key factor that will affect uptake is the price of these fuels. Other questions that need to be addressed are related to local and global availability, production techniques, and safety and reliability concerns. The alternative fuel options available today or in the foreseeable future include:
- liquefied natural gas (LNG)
- liquefied petroleum gas (LPG)
- dimethyl ether (DME)
- synthetic fuels
- grid electricity
- nuclear propulsion, and
New fuels often require new on board systems and machinery, and shifting from one fuel (heavy fuel oil (HFO), marine diesel oil (MDO) to another (e.g., LNG) will take time, and may lead to unforeseen technical issues and delays for pioneers. Thus, a fuel that can be introduced without significant modifications to the machinery and storage facilities has the advantages of simplicity and low capital costs.
LNG was already utilized as a fuel by LNG carriers in the 1960s to take advantage of the fuel available on board in the form of boil-off gas. The first LNG-powered vessel was built in 2000, and at present there are about 75 LNG-powered ships in operation, excluding LNG carriers, and another 80 under construction. In addition, 40 ships have been designed to be ready for LNG retrofit. The growth in LNG-powered ships is expected to accelerate towards 2025. LNG is currently a particularly attractive fuel option for vessels operating in North American waters that have to comply with the Tier III NOX emission standards. The adoption of a 0.5% sulphur limit in European waters in 2020, in addition to the current ECA, could spur accelerated growth of the LNG-fuelled shipping fleet. A number of other sulphur-free fuels can also be used as a substitute for oil in dual-fuel engines. Amongst them, biodiesel, LPG, and methanol are of particular interest because they also offer significant reductions in emissions of NOX and particulate matter (PM).
Fuel availability and pricing will be decisive factors for widespread adoption of any alternative fuels in shipping. The development of bunkering infrastructure is a prerequisite to allow large, ocean-going ships to use alternative fuels. Other factors, such as the high cost of building or retrofitting dual fuel ships, the size of fuel tanks, and concerns about safety, may limit the uptake of such fuels.
A controversial option for powering large vessels is nuclear power. Its main advantages are virtually zero CO2 emissions and a propulsion system suitable for ships that need to be self-supporting for long periods. However, due to significant controversy around nuclear power, and public concerns related to potential consequences from accidents, it seems unlikely that nuclear propulsion will be widely adopted in shipping within the next 10-20 years. The outlook may change if societal acceptance of nuclear power increases and there is stronger policy push to reduce gaseous emissions from shipping.