Turning tides: how the shipping sector is going green
It is too early to determine how the shipping sector will be exposed to a direct emission cost, yet it seems very likely that this is on the horizon. The overarching idea is that charges on pollution will encourage vessel owners to reduce emissions to avoid or mitigate such fees.
Given the expectation of a global carbon levy, what options are already available in the maritime sector to reduce emissions?
Several machinery energy saving systems have been available for a long time in the shipping sector. These tend to enhance the performance of the main engine, auxiliary engines, or boiler, depending on vessel type and operational profile. For instance, a waste heat recovery system saves around 3-5% energy by exploiting the thermal energy in exhaust gases produced by the main engine. The waste heat is reused to generate electricity via a steam turbine or generate hot water to heat the vessel. This reuse lessens the workload on either the auxiliary engines or boiler, respectively. If the main engine is connected to a shaft generator, this system would ultimately benefit the main engine as it generates electricity from the rotating shaft between the main engine and propeller to unload the auxiliary engine.
The use of shore power when a vessel is at port, commonly referred to as cold ironing, is another measure to reduce need for auxiliary engines. However, the lack of global infrastructure is a limiting factor.
Hull structures and propulsion systems
There are several types of improvements that can be implemented on hull structures and propulsion systems, again depending on vessel type and operational profile, to lower emissions from a ship. A bulbous bow generates waves in a manner that reduces resistance. Yet not all ships have this design. The bulb benefits large vessels with longer periods in transit e.g., cruise ships, container ships and tankers. A retrofit of the bulbous bow is a measure to optimise the hull to a new operational profile, typically for a lower design speed. A retrofit of bulb may decrease fuel consumption on a main engine by up to 5% on these three types.
When a vessel is altering its design speed, it also makes sense to adapt the propeller-rudder system too. Enhancements to the propulsion system include contra-rotating propellers, various types of ducts, pre- and post-swirl stators, fins, boss cap fins, and spoilers. Even though these have not reached full commercialisation, fixed sails fall under this category as well. Depending on vessel design and environmental conditions, fuel savings from utilising sails can potentially reach as much as 20%.
In addition, vessel crew can reduce CO2 emissions significantly by undertaking specific operational measures. Running the machinery at optimal engine load, slow steaming and well-established maintenance routines can have a significant impact. When sailing, accurate weather forecasting, carefully planned routes, as well as trim and draft optimisation, have additional and considerable energy saving effects.
According to Green Voyage 2050, slow steaming alone may have a fuel saving potential of up to 50%, due to the exponential relationship between vessel speed and fuel consumption. However, a speed reduction yielding this result is not always achievable as it conflicts with the tight schedule seafarers are required to keep.
Point versus range optimisation
Observing the speed versus fuel consumption is one of the key measures to assess the efficiency of a vessel. In this regard, there has been a shift in the design philosophy of ships. Older vessels active today are commonly designed to operate very efficiently with one speed in mind. This optimised point, the design point, considers several factors such as draft, ship dimensions, environment, and operation. Newer vessels, on the other hand, are often designed to suit a wider spectrum of speed and other given conditions.
As illustrated in Figure 1, a narrow design range will be more efficient when operating at the design point. In practice, it is inevitable that vessels operate in different conditions. By having a wider design range, i.e. being range optimised, fuel consumption will not be as efficient at the design point, but the overall fuel consumption will be less compared to a point optimised vessel.
Market analysts have a wide-spread belief that low- and no-carbon fuels such as ammonia, hydrogen and battery technology will play a providable role in decarbonising the maritime transport sector. However, these technologies are novel and currently come at a high financial cost and risk, and lack necessary infrastructure for large-scale deployment. As the EU Commission highlights in its FuelEU Maritime directive proposal, hydrogen and ammonia are likely to reach commercial maturity first in the 2030s.
Battery technology also needs further development to be a competing GHG-neutral substitute. Fossil fuels have a higher specific energy density, i.e. higher energy content per unit mass, than current battery technology. As vessel designs are limited by weight, current battery solutions are only eligible for hybridisation and for full-electric vessels travelling short distances.
In addition to the transition from fossil fuels to alternative fuels, there is a lot of ongoing research into energy recovery systems. Such systems include sails, Flettner rotors, kites, and solar panels. They recover the energy from wind and sun respectively. Reverting back to sails, or in actuality vertical airfoils, is a promising technology that is reaching maturity and commercialisation.
A combination of an alternative fuel and an energy recovery system might contain the energy required to run a vessel without compromising on optimal operations. However, full maturity of these technologies is yet to be realised.
Difficult path to 40% emissions reduction goal
Today, there is no conspicuous solution for the global maritime industry to hit its carbon intensity reduction goal of 40% by 2030. Whether the maritime industry is to be governed by the EU ETS or the ICS proposal, vessel owners must prepare themselves to participate in a system which will incentivise lower emissions.
Neither ammonia, hydrogen nor battery technology are expected to be a commercially viable solution soon but energy recovery systems, such as vessels equipped with sails, could be used in conjunction with alternative fuels to reach full operability of vessels. Until then, however, ship owners must make use of the alternatives available on the market today to help lower their carbon footprint as well as associated costs that impending new regulations may bring along.