Maritime transport is commonly presented as the cleanest mode of transport. However, the reality is less obvious. In order to boost the ecological transition of this sector, the IMO has set binding targets. A revolution is therefore underway to have cleaner modes of propulsion.

A necessary ecological transition

It is true that maritime transport is much more efficient in terms of CO2 emissions than road transport. However, its environmental footprint is much larger if we look at the sulphur and nitrogen oxide emissions induced by the consumption of heavy fuel oil.

The IMO has taken the measure of the on-going ecological transition. It has therefore committed to reducing the total volume of greenhouse gases (GHG) emissions from shipping. The goal is to reach half of 2008 GHG emissions level by 2050.

To comply with these new standards, ship-owners have no choice but to make investments. There areseveral options:

  • turning to low-sulfur marine fuel oil: cheaper than conventional heavy fuel oil, its carbon footprint remains high;
  • installing smoke scrubbers: such devices are capable of capturing up to 90% of sulfur emissions;
  • change to alternative propulsion modes.

The need for investment

During the life of a vessel, shipowners are faced with regulatory changes and the variability of energy costs. Therefore, spending on research and development for alternative propulsion systems must be considered as an investment.

The maritime transport sector underwent a first change with the multiplication of electrically propelled ships, known as “all-electric ships“. It is true that electric propulsion is more efficient than conventional propulsion. However, the gains obtained are low compared to the IMO objectives.

Other technologies, currently in service or under development, can generate fuel-consumption reductions, meaning GHG emissions reductions:

  • sailing propulsion: several carriers have opted for hyper-efficient cargo sailing ships, some of them are able to carry several hundred TEU;
  • wind energy is also used via towing kites, or Flettner rotors, using the Magnus effect to supplement the propulsion of ships, thus reducing the load on propulsion engines and therefore their consumption;
  • wind energy combined with solar energy. The EnergySail technology developed by Eco Marine Power, for example, uses rigid sails equipped with solar panels;
  • wave energy: installed at the back of the ship, an articulated hydrofoil is driven by the waves. The movement generates useful energy for the ship, which leads to a reduction in fuel consumption (such technology has been developed by Blue Fins and Ifremer).

Towards a revolution

The use of other fuels, as substitutes to heavy fuel oil, is another option for the future:

  • The combustion of liquefied natural gas reduces SOx emissions by 100%, NOx by 80% and CO2 by 20% compared to heavy fuel oil. Although the conversion of ships from heavy fuel oil to LNG has been mastered, it still involves a fossil fuel that doesn’t eliminate most of the GHGs;
  • Several challenges still need to be overcome to use hydrogen. First of all, for the same amount of energy, liquid hydrogen takes up to four times more volume than heavy fuel oil. However, this difficulty is partially offset by the increased efficiency of hydrogen fuel cells, compared to diesel engines, and by the smaller size of the propulsion system. The current power of hydrogen fuel cells only allows them to be used on small ships. Finally, and most importantly, this type of propulsion only makes sense environmentally if it uses “green hydrogen“, the production cost of which is absolutely not competitive today.

Although it offers great promise in terms of GHG emissions, the hydrogen sector is not mature yet. However, while the OECD estimates that international freight volumes will increase more than fourfold between now and 2050, it now seems to be the most credible solution for achieving the objectives set by the IMO.

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