Decarbonization perspectives for navies

The naval sector is rarely mentioned in the discourse about decarbonization. But while navies are typically exempt from greenhouse gas (GHG) regulations, the topic is not absent from their agenda. DNV has published a white paper titled “Alternative Fuels for Naval Vessels”, which examines general trends in the search for alternative ship fuels and propulsion technologies and looks at the pros and cons of each proposed solution in the context of the specific requirements of naval ships. The paper is intended to provide comprehensive decision support for naval retrofitting, optimization and newbuilding projects. “Climate change has already heightened inter- and intra-state tensions and competition over limited resources,” the white paper points out. Military decision-makers must therefore keep abreast of the developments in commercial shipping.

A detailed analysis of alternative fuels

The DNV white paper is based on a wide range of public-domain information sources – including the DNV Maritime Forecast to 2050 – as well as a survey conducted among 130 stakeholders from navies, shipyards, OEMs and fuel suppliers in twelve countries. It examines the entire range of present and foreseeable future options to reduce GHG emissions from ships and their carbon reduction potential, and analyses the uptake of alternative energy sources across the world fleet. Each fuel type – LNG, hydrogen, ammonia, methanol and LPG as well as electricity, biofuels and nuclear power – is examined in depth, highlighting key challenges, implementation status and the regulatory environment.

Naval vessels must meet special requirements

Because of their unique purpose, naval vessels, and in particular, combat vessels must meet a number of special requirements that set them apart from commercial ships: They must be able to operate under direct threat, at high speeds and for extended periods with the only possibility for refuelling actually at sea. Independence, endurance, low detectability, high agility and manoeuvrability even in a damaged condition are of vital importance. The choice of fuel must account for the size, mission and payload of the given ship type, the range and the power demand of the military systems on board – such as radars and weapons – and potential exposure of fuel to hostile fire. All these requirements complicate the search for sustainable propulsion technologies. 

“Alternative fuels are the most effective measure to fully decarbonize in the future, but practical considerations such as logistics, fuel availability, fuel change flexibility and design impacts are critical factors in determining the feasibility of the different low- or zero-carbon fuels for the naval segment,” explains Christian von Oldershausen, DNV Maritime Segment Director for Navy.

Submarines and the pros and cons of nuclear reactors

Nuclear propulsion has been used by the U.S., British, Russian, French and Chinese navies for decades because of the speed and endurance it gives to combat vessels, especially submarines. It is in essence carbon-free but extremely expensive. Notwithstanding the strategic and tactical advantages, demand remains low since radioactive waste is seen as an environmental threat and public opposition as well as proliferation fears may prevent the use of nuclear power on a larger scale. 

On the other hand, the white paper says, submarines “have taken the lead in terms of the adoption of alternative fuels, thanks to the emergence of the air-independent propulsion (AIP) system in the mid-20th century”. AIP systems are compatible with alternative fuels and fuel cells and considered as a viable alternative to nuclear propulsion. 

Survey results deliver key insights

The paper expressly avoids making specific recommendations. Its declared mission is to provide “an overview of the current use and comprehensive factual summary of the advantages and disadvantages of the various alternative fuels” to “enable informed decision-making”. The survey conducted for this document produced valuable insights, which are visualized in charts and graphs.  

While the number of naval ships running on alternative fuels remains rather small, more than 83.3 per cent of survey respondents saw biofuels as a more realistic option for naval ships than ammonia, methanol, hydrocarbons or other power sources, especially since drop-in biofuels do not require any retrofits.  

Combat vs non-combat ships

The paper differentiates between combat and non-combat or support vessels. The latter typically operate closer to shore, travel shorter distances, are less exposed to hostile action and are in many ways comparable to commercial ships. A majority of survey participants opined that non-combat vessels will be the first to embrace alternative fuels, rather than fighting vessels such as frigates and destroyers with their highly specialized needs. 

Fuel availability and fuel change flexibility were ranked as top concerns by 79.2 per cent of respondents, a clear message to designers of future naval vessels.

Key criteria for naval shipbuilding

The main goal in the search for alternative naval fuels is to “improve combat capability and operational flexibility”, the white paper stresses; current abatement measures will soon cease to fulfil the decarbonization goals, and “the use of alternative fuels will be necessary to meet the [IMO] GHG trajectory. This also means that the ship should be designed to allow for the needed upgrades or fuel changes later in its lifetime.” 

Key drivers for the future use of alternative fuels are operational in nature, the paper concludes. Flexible fuel sourcing options, a robust supply chain, applicability to specific mission profiles, and asset safety are key criteria. The paper therefore extensively discusses the status quo of alternative fuels in civilian shipping. 

DNV has developed a robust methodology for the commercial world to help shipowners transit into a decarbonized setting safely and sustainably. The same methodology can be adapted for a naval setting. The white paper provides guidance for carbon risk assessments and newbuilding projects. Jan Christian Kaack, Vice Admiral, Chief German Navy, Commander Fleet and Supporting Forces, summarizes: “This white paper provides an excellent starting point for us to work together to protect our environment and at the same time ensure the operational readiness of our navies.”

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