sustainability transport

Five options for low carbon shipping

This year I’m looking at transport a bit, and I’ve been focusing on road transport as that’s a large and obstinate source of emissions. I’ll talk about rail and aviation too along the way, and today I wanted to draw a ‘transport innovation of the week‘ from the world of shipping.

In terms of carbon, international shipping is relatively modest at around 2.8% of global emissions. (It may be higher – a UN report a few years ago suggested it was consistently underestimated and may be around 4.5%.) But the weight of goods we ship is projected to grow dramatically in coming decades, and every sector needs to play its part in bringing emissions down. Since ships run on heavy oil or maritime diesel, they’re also a source of pollution. Areas around ports are particularly affected by ships running their diesel generators while moored. So there’s a double incentive to transition to cleaner energy.

Shipping isn’t covered by international climate agreements and, like aviation, sets its own targets within the industry. Unlike aviation, which has basically given itself a free pass on climate change, the shipping industry is quite ambitious: it aims to reduce emissions by 50% by 2050. In difference in ambition is probably mostly down to the options available. There are still very few alternatives for low carbon aviation, whereas shipping has a number of possible technologies to choose from. There are lots of efficiency savings, and a number of ways to power a ship without fossil fuels. Here are five:

Methanol is one of the easiest alternative fuels to make, and is a good way to reduce emissions and sulphur pollution. In 2016 the world’s first methanol cargo vessel was launched in South Korea. It’s actually a multi-fuel ship that can burn methanol, diesel or fuel oil, so how clean it proves over its lifetime will depend on how the operator uses it, but it was commissioned by a Norwegian firm committed to cleaner transport. Methanol is a promising fuel because it’s widely available, relatively cheap, and it’s possible to retrofit ships to use it. Stena Line is adapting some of its ferries to run on methanol, with the first entering service in 2015.

Liquid Natural Gas (LNG) is a much cleaner burn than liquid fuels, and there’s a growing interest in using it for ships. The first gas powered container ship was launched in 2015, the Isla Bella, it’s green gas tanks clearly visible in the photo below. Cruise and ferry companies look like the main customers, and two new gas ferries were ordered by an Italian company last week. Again, this is cost effective and the global infrastructure is already in place. LNG shipping knocks a third off CO2, and reduces nitrogen oxide (NOx) pollution by 90%. Unfortunately its methane emissions are higher, and it is still a fossil fuel. A 30% cut in CO2 is better than the present situation, but in the long term it doesn’t go far enough and LNG is best considered a bridge technology.


Hydrogen offers the much more radical promise of zero carbon shipping. The idea of a ‘hydrogen economy’ remains popular for transport generally and some suggest that ocean vessels are the natural place to start. The first hydrogen boat has been operating in Germany since 2009, but it’s a tourist boat rather than a ship, and significant obstacles to hydrogen remain. There are few port facilities for refueling. Hydrogen is also a low density fuel, so it would take up more space on board ship. Perhaps the most interesting approach is to store renewable energy in hydrogen fuel cells the size of a shipping container, which ships could then plug in and run off, possibly topping them up with a LNG hybrid system. It’s still largely experimental at this stage, so we shall see.

Nuclear power is a proven technology at sea, used in submarines and aircraft carriers. It’s never been cheap enough to catch on at the commercial level, and there’s only one civilian nuclear ship in the world at the moment as far as I know – the Russian ice-breaker Sevmorput. Nuclear ships have been expensive to insure and historically unwelcome in port because of safety fears, so on the face of it there’s no future for nuclear shipping. But given the environmental benefits, we shouldn’t be too hasty. All the innovation around nuclear power at the moment is around small modular reactors, which would finally deliver the missing economy of scale. We’ve been waiting for them a long time, so I won’t hold my breath. But if they ever do materialise, I would expect renewed interest from the shipping industry.

Wind was the original power source for international shipping, but the age of sails is behind us now and it’s hard to imagine how wind power could be used at the scale of today’s global shipping networks. There are opportunities for all sorts of smaller vessels though, and there are a number of prototypes for sail powered shipping. The biggest contribution from wind is likely to be supplementary power. A kite sail can be retrofitted to existing ships and trim 10% off their fuel consumption. More unusual are Flettner-rotors, a 1920s idea that was recently rediscovered and applied at large scale on E Ship 1. Appropriately designed to carry wind turbines, E Ship 1 has four 25 metre tall rotors that turn wind power into propulsion, reducing fuel needs by 30-4o%. A small price to pay for looking like an upside down coffee table.


Of course, the best way to reduce emissions from shipping is to reduce shipping in the first place, and produce more things locally. But we’re always going to need shipping of one sort or another, and there are plenty of ways to make it less ecologically damaging.


  1. Some years ago I read of a proposal for ships to be powered by a vertical axis wind turbine. These would be entirely powered by wind but, unlike conventional sailing ships, would be independent of wind direction. The concept of such a turbine, but not for this application, is described at . It looks from that article as if further development is still needed to make it viable though.

    1. There are plenty of opportunities for sail, that’s for sure. I suspect that it will mostly be hybrids though, with wind power used for supplementary power. There are a few reasons why: the fastest sailing ships, the tea clippers, were as fast as modern vessels, but most sailing ships were much slower.

      Speed isn’t everything – some of today’s biggest ships creep along at 12 knots to save fuel, half the speed they could reach if they’re in a hurry. But at least they know in advance how long they’re going to take. Sailing vessels depend entirely on the wind and you wouldn’t know in whether your journey was going to take one month or five. Not many businesses could run their supply chains with that kind of variability of supply.

      You’re also limited by prevailing winds, which would massively disadvantage many parts of the world that are just harder to reach by sail.

      On a very practical level, sailing ships are tricky to negotiate in and out of port. So you’d want a motor for docking anyway. Might as well go for a methanol or hydrogen fuel cell hybrid, and you’ve got a backup for low winds.

  2. Steam engines in ships seem to have gone out for no particular good reason. In a marine context, steam, either in turbine or reciprocating forms, is more efficient than in a railway context, since they can condense and operate down to ambient temperature, which comes closer to the optimum Rankine cycle.

    The great advantage of steam engines is that combustion is external, which means that a variety of fuels (including biowaste) can be used and that the process can be better controlled to reduce the production of particulates and NOx.

    The main difficulty is in rebuilding the manufacturing and support infrastructure. Reciprocating steam engines have a relatively small components count compared to internal combustion machines; with quantity production, there are potential cost savings, especially with the use of manufacturing techniques such as CNC and 3D printing for patternmaking.

      1. There are liquid fuels made from biomass. Steam engines are not fussy like internal combustion engines. Anything that will burn can be used as fuel

        1. LHG carriers are often steam turbine powered burning the boil off gas (BOG) which would otherwise be wasted. But newer dual fuel ic engines are replacing them as they are thermally more efficient.

          Also there aren’t many steam turbine experienced crew to maintain them.

          1. The argument about thermal efficiency was an important reason given for getting rid of team in the 1960s. It is the same reason used for 25kV railway electrification as against 750V..

            However, I wonder if that is the real reason? It is overall costs that matter in the end, and there are many other factors to be taken into account in that equation.

            New steam locomotives were supplied to tourist railways in Switzerland and Austrian in 1993. There were designed to run on diesel fuel. Much to the manufacturer’s surprised, it then turned out that they were using less fuel than diesel-electric locomotives doing the same work. They could tell from the amount being put in the fuel tanks. An audit was carried out which established the causes, which were might be described as second-order effects. The diesels were then put aside for reserve use.

            One of the benefits of external combustion is that it is easier to comply with emission standards.

          2. Sadly among the host of replica steam engines currently being built the 5AT won’t be completed to create a modern loco to complete with the ubiquitous Class 66s

            But schemes like the Fairratt on the Welsh Highland may give a showcase of what is possible.

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