Table of Contents
Introduction
Batteries more often than not are a component in something that we all use on a daily basis. Batteries are devices that use chemical energy to store electrical energy. They consist of three main components, the anode, the cathode, and the electrolyte, each of these have specific characteristics that when combined in a specific way function to create a power source. The anode and the cathode, often referred to as electrodes, are typically made of metals that act as terminals that can interact together to generate the flow of electricity. The chemical reactions that occur on the electrodes create the flow of electricity in the system. The electrolyte is the medium that then allows the flow of electrical charge between the cathode and anode.
Battery technology is one of the many options that has piqued the interest of the maritime industry as it is striving towards building more environmentally friendly ships of the future. With industry wide increased focus on decarbonisation the potential use of alternative fuels, cleaner energy sources, emission-free solutions such as battery technologies are gaining momentum. Numerous stakeholders are continuing to find ways to adapt to the shifting trends in energy management and propulsion technology. This trend has been highlighted by the increase in fully electric vessels that have been created over the last decade., Based on data from Statista, there were only 10 ships with fully electric and hybrid battery systems in 2010. As of 2020, the figure is at 398.1
Shipboard applications for battery technology
Shipboard applications and the use of battery technologies is not a new concept within the industry. Countries such as France, Norway, and Japan have already integrated batteries onboard various ship types including container vessels, tankers and passenger ferries. Although modern-day batteries are still quite limited in their use due to distance requirements, in areas where voyage distances are shorter and the focus on reliability and power output are of higher priority, batteries have been identified as an effective option. This trend is evident in the passenger vessel and workboat markets where the use of battery technology has been well implemented and proven its suitability.
While fully electric ships have been introduced to us in recent years, the application of batteries in ocean-going vessels will continue to be used as a part of a system and not as a standalone technology in itself at this stage. This can be seen in ocean shipping, where batteries are often used as a secondary power option or as a part of a hybrid power system rather than the primary and only power option. Hybrid systems are the combination of the ship’s engine and a battery pack. In this setup, the engines are operated at base load conditions and the batteries are used to compensate for the fluctuating loads. This manner of combined operation is known as peak shaving.
This approach of peak shaving has been designed for the efficient management of the ship’s electrical load and for optimising the vessel’s performance. When vessels are approaching the port, or when onboard operations require immediate intensive electrical loads. This option is effective in efficiently managing the requirements of the energy consumers onboard. It allows vessels to reduce their fuel and maintenance costs and has been proven to deliver an estimated 15%-30% savings.2
Beyond Lithium-Ion: alternative batteries for shipboard applications
Lithium-Ion batteries are currently considered the most advantageous option available in the battery market within the maritime industry, but that is not to say they are the only option that exists. These batteries are beneficial due to their use for both electrical energy storage and distribution, this is undoubtedly a factor why they are the most widely used option within the maritime industry right now. These batteries consist of a cathode, an anode, a liquid electrolyte, and a separator.
Despite the benefits offered by this battery type, the main notable disadvantage and concern regarding Lithium-Ion batteries is the risk of thermal runaway. This is defined as the rise in temperature that affects the condition of the battery leading it to a further increase in temperature. This risk is what requires lithium-ion batteries to be installed with thermal monitoring and load management systems to ensure the safety of the vessel and its crew. These systems could greatly benefit from being designed to adjust to the electrical load requirements of the ship. Due to the drawback of not offering this instantly, the requirement of an increased electrical load translates to an increase in the number of batteries on board, which ultimately take up more space on board as well as an increased cost.
Despite many battery technologies being in the early stages, predominantly many are still ongoing in research and development stages. The industry however is becoming more open to the adoption of various battery technologies as they look towards the development of emission-free ships. The American Bureau of Shipping has recently highlighted the growing potential of battery technologies, and have presented several configurations that can prove their potential against today’s more common lithium-ion batteries. The technologies mentioned that have the potential improve the battery power market included metal-air batteries, red-ox flow batteries, ammonia batteries, and solid-state batteries.3
Metal-Air Batteries
Despite these being in the early development stages, metal-air batteries are gathering considerable attention from industry stakeholders due to the higher energy density that they offer compared to lithium-ion batteries. These batteries are designed like a traditional battery except that the traditional solid cathode has been replaced by an air cathode. The metal anode used in metal-air batteries is typically made of either zinc, aluminium, or lithium. However a downside to this battery type is the instability of the electrolytes and the electrodes which ends up limiting the life of the battery. The poor cycle life of the current design of metal-air batteries also makes them non-rechargeable which as a battery option does not make them attractive for implementation at this stage.
Red-Ox Flow Batteries
Red-ox flow batteries or reduction-oxidation flow batteries operate based on a chemical reduction and oxidation reaction between two electrolytes. In this technology the anolyte and the catholyte are transferred to the battery cell from tanks, where they then interact over an ion-selective membrane. These batteries have drawn interest from industry stakeholders as a result of them being safer than lithium-ion batteries due to having a lesser level of risk in terms of thermal runaway.
The design of red-ox flow batteries utilises two tanks wherein the amount of energy storage is dependent upon the amount of electrolyte available in the tanks. They are easily scalable for future load requirements, but will also require space and weight considerations when installed for shipboard applications. The low energy density of red-ox flow batteries as compared to lithium-ion batteries is also a factor that affects the usefulness of the batteries. There are two designs that are currently being developed for this battery type. These are the True red-ox flow batteries, which utilise vanadium-vanadium and iron-chromium as the electrolytes, and Hybrid red-ox flow batteries which utilise zinc-bromine and zinc-chlorine as their electrolytes.
Ammonia Batteries
Current ammonia battery technology is being developed in two ways, thermally regenerative ammonia batteries, and ammonia flow batteries.
In the design of thermally regenerative ammonia batteries, the electrolyte used is added with ammonia and utilises electrodes in a standard cell configuration. This battery discharges like a normal battery by producing energy through a chemical reaction and recharges thermally by using heat to vaporise ammonia allowing it to return to its recharged liquid state. It is potentially useful in recapturing waste heat and creating a fully sustainable system for energy production. However, the low efficiency and poor cycle life of thermally regenerative ammonia batteries require it to be further developed for it to become a mainstay in the maritime industry.
Ammonia flow batteries operate using a concept similar to that used in reduction-oxidation flow batteries. However this battery type utilises ammonia as an addition to the anolyte, to produce a potential difference between the electrolytes creating electricity through the chemical reaction. The technology here is still in the early developmental stages and is tipped to be designed as an alternative to the thermally regenerative ammonia battery.
Solid-State Batteries
Solid-state batteries are designed with a solid electrolyte, this is the main difference between this battery type and current lithium-ion batteries. The use of compact solid electrolytes makes the battery lighter and less prone to the risk of thermal runaway. At the moment, lithium is a popular choice to use for the anode of solid-state batteries, and inorganic lithium-ion conductive ceramics materials such as Garnet and Sulphide glass are the leading options for solid-state electrolytes.
The downside of solid-state batteries is the poor contact design of the electrodes and the electrolyte which causes high resistance and poor conduction leading to poor cycle life and may further worsen to rapid battery deterioration. This concern also includes the interphase layer between the electrolyte and electrodes which may affect the performance of the battery in the long run. For the optimal operation of these batteries, they are required to operate at a higher temperature compared to lithium-ion batteries due to their generally lower room temperature conductivity. This requires the addition of a temperature monitoring system for solid-state batteries. Combining this with the cost of materials and development, solid-state batteries will require more work for them to be a staple in the maritime industry.
The adoption of battery technology within the maritime industry has the potential to rapidly increase in the coming years due to a range of factors. The increased environmental focus industry wide, with bodies such as the International Maritime Organisation (IMO) striving towards net zero and substantial reductions in greenhouse gas emissions coupled with the increasing developments and improvements within battery technology. These factors are bound to play a role in the implementation and uptake of this technology option.
Despite the increasing cost of lithium, the advancements in the automotive industry have drastically reduced prices for battery cells. As a result this allows the maritime industry to benefit from these reduced costs for development. The active support of class societies such DNV GL, ABS, Bureau Veritas, and Lloyd’s Register also benefits the integration of battery technologies in today’s global merchant fleet. These organisations have published their respective guidelines for the application of battery technologies onboard ships. The technical and regulatory support from these authorities makes the technology a more appealing option as the industry continues to navigate towards a more environmentally sustainable direction.
Conclusion
The wider adoption of battery technologies continues to have its challenges. Technical hurdles involve the maintenance, monitoring, and management of the shipboard batteries relating to the safety and efficiency of their long-term use. The need for various systems to handle potential issues in terms of battery management, fire safety and cooling, charging, and lifecycle management need to be developed to ensure the widespread adoption of battery technologies in the industry. Economically the adoption of these technologies are challenged by the initial expenditure and associated costs within research and development in this specific area. However, it is important to note that the cost for the maintenance and operation of battery systems is cheaper than that of internal combustion engines in the long run.
With the global market for fully electric and hybrid ships in 2026 expected to reach up to nine billion US dollars,4 battery technology applications are an attractive option for companies. The long term financial benefits of these systems alongside their effectiveness as a marine energy storage solution is promising. Based on current applications, the future of battery technologies in the maritime industry can be seen in hybrid power systems where battery technology can be used as an option for environmentally restrictive areas as well as vessel performance optimisation. The use of operational approaches such as peak shaving with battery technologies for energy management may soon become a mainstream component in the maritime industry, especially for ocean-going vessels as it can act as a driver for the decarbonisation of the maritime industry.
References:
- Number of ships with batteries in operation and on order worldwide from 2010 to 2021, Statista, December 2021
- The Future of Batteries in the Marine Sector: What Lies Beyond the Horizon? University of Southampton, November 2020
- Emerging Battery Technologies in the Maritime Industry, American Bureau of Shipping, November 2021
- Projected size of the global electric ship market between 2020 and 2026, Statista, September 2021
