Swedish researcher Joakim Haraldsson of Lund University has proposed aluminum as a new sustainable fuel for maritime vessels. He has analyzed dozens of scientific papers, made appropriate calculations and concluded that this metal could play a significant role in reducing CO2 emissions in shipping. Naturally, practical applications of this technology would require addressing a host of technical and economic challenges. If that could be pulled off, however, not only a new source of clean energy would be obtained but it would be possible to create a closed-loop system using a material that can be recycled multiple times.
Today, the global merchant fleet depends almost exclusively on heavy fossil fuels. International shipping consumes some 2,560 TWh of energy every year, emitting circa 699 million tons of CO2, or approximately 3% of all global greenhouse gas emissions. Moreover, ship engines release sulfur and nitrogen oxides, which pollute the air in coastal areas. The International Maritime Organization aims to make shipping climate neutral by 2050.
However, existing alternatives, such as biofuels, hydrogen, ammonia, and batteries, have their limitations. Some areas lack resources, in others energy density is too low, and there are regions facing storage and transportation challenges. All that drives scientific search for new solutions.
Aluminum could be one such solution. The idea of using it as a fuel is not new—the first experiments date back to the mid-20th century. But Haraldsson is the first to thoroughly evaluate this concept specifically for maritime transport.
In itself, aluminum is not a source of energy—it only functions as a sustainable energy carrier. Energy—for example, electricity generated by solar or wind power plants—could be “injected” into the metal during its production. This energy is then released on board the ship through oxidation of the aluminum. That reaction can be triggered in two ways: by burning the metal in oxygen or by its interaction with water. In the latter case, hydrogen is also released. Both processes generate large amounts of heat, which can be used to power turbines, generators or engines.
The main technical challenge lies in the fact that, when exposed to air or water, aluminum forms a thin film of oxides, which hinders further reaction. To overcome this drawback, the metal must be activated—for example, by grinding it into powder, adding alkali or salt, or heating it to cause its melting.
The study in question also describes the full cycle of using aluminum as a fuel. After the reaction, solid products—aluminum oxide or hydroxides—remain on board. These are not discharged into the sea, but are collected and returned to port. Back on base, these compounds can be reconverted into aluminum metal using electrolysis. This creates a closed cycle: the metal is used to generate energy, then it is recycled and returned to the system. However, putting this process into practice would require new port infrastructure to store the fuel and receive the reaction products.
Estimates show that in terms of energy storage aluminum performs twice as good as methanol and ammonia, although it weighs more than fuel oil. A container ship traveling from China to Europe would require approximately 6,000 tons of aluminum. The resulting reaction products would take up additional space (about 1% to 2.5% of the ship’s cargo capacity). Furthermore, as the reaction proceeds, the ship would put on some additional weight, as aluminum oxides are heavier than the parent metal. This would increase energy consumption, if only by a few percent.
Another problem is aluminum availability. To completely replace fuel oil in global shipping, the industry would require approximately 300 million tons of the metal every year. Currently, annual production of aluminum stands at about 71 million tons worldwide, and most of that output is used in construction, transportation, and manufacturing. Waste recycling would only cover up to 17% of potential demand. This means that production of primary aluminum would have to increase significantly, which would require around 6,000 TWh of electricity per year, or roughly 2.3 times more than the current consumption of the entire global shipping industry. In theory, this amount of energy could be provided by the development of solar and wind generation.
Today, aluminum is inferior to fuel oil and methanol in terms of the cost of the energy produced. But, as time goes by, the situation could change. For instance, the use of aluminum scrap, which is difficult to recycle using existing methods, could reduce the cost of the fuel. Furthermore, new aluminum production technologies (such as inert anodes) and more efficient propulsion systems on ships could also make the commercial aspect of this idea more attractive.
Haraldsson himself emphasizes that his work is only the first comprehensive evaluation of this concept. Many parameters still need to be refined, and it will take some time and effort to bring the technology to an industrial-grade level.
