From the 15th to the 17th century, known as the Age of Exploration, and continuing to the present day, ships have been pivotal in transporting goods and services globally. Currently, about 90% of the world's trade volume is transported by shipping, which relies heavily on approximately 300 million metric tons of heavy fuel oil (HFO) annually, according to the International Maritime Organization (IMO). This extensive use of HFO results in substantial carbon emissions, with shipping contributing about 3.1% (1130 Mt CO2) of global greenhouse gas (GHG) emissions due to its high fossil fuel content. Specifically, HFO accounts for 72% of fuel used in shipping, marine diesel oil (MDO) for 26%, and liquefied natural gas (LNG) for 2%. Additionally, ships are significant sources of sulfur oxides (SOx) and nitrogen oxides (NOx), which contribute to air pollution.

In response to these environmental challenges, the IMO launched a groundbreaking initiative in July 2023, aiming for net-zero emissions from ships by 2050. This ambitious goal surpasses the previous 2018 strategy, which targeted a 50% reduction in CO2 emissions by 2030. To achieve this vision, shipping companies are actively exploring alternative zero-emission energy sources, including hydrogen, ammonia, methanol, solar, biomass fuels, and wind power. Furthermore, all newly ordered ships must be capable of operating on zero-emission fuels by 2040.

Alternative Sources of Shipping Energy

Wind

The use of wind energy to power ships dates back centuries, but modern technology has revolutionized how we harness this natural power, reducing reliance on fossil fuels and enhancing environmental sustainability. Traditional sails, made from fabric, capture wind to propel ships forward. Innovations have led to advanced materials and rigging systems for these sails, maximizing efficiency.

Today, wind-assisted propulsion systems supplement primary engine power with wind power, significantly cutting fuel consumption and emissions. Flettner rotors, cylindrical structures that spin around a vertical axis, utilize the Magnus effect to provide thrust. Large, controllable kites fly at high altitudes, where winds are stronger, generating significant pull to aid propulsion. Rigid sails, resembling aircraft wings, and advanced soft sails, made with high-tech materials, further enhance performance and durability.

Hybrid systems combine wind power with conventional engines, using advanced software to optimize energy use. This approach reduces greenhouse gas emissions, contributes to cleaner air, and offers long-term cost savings despite initial installation costs. Retrofitting existing ships with these systems poses challenges, but new vessels can be designed to incorporate them from the outset.

Notable examples include the Eco Flettner Project and the MV Afros, which demonstrate significant fuel savings using rotor sails. The SkySails system has shown impressive efficiency improvements by deploying large kites for additional thrust. By integrating wind propulsion, the shipping industry moves toward more sustainable and efficient operations, significantly reducing its environmental impact.

Solar

Solar energy is another promising alternative for powering ships. Solar panels installed on the deck and superstructures of ships capture sunlight and convert it into electricity, which can then be used to power onboard systems and supplement propulsion. Advances in solar technology have led to the development of more efficient and durable photovoltaic cells, making solar energy a viable option for reducing reliance on fossil fuels.

Hybrid systems that combine solar power with traditional engines or other renewable energy sources can significantly decrease fuel consumption and emissions. Solar power can be particularly effective during daylight hours and in regions with high solar irradiance. One of the notable examples is the MS Tûranor PlanetSolar, the world's largest solar-powered boat, which has demonstrated the potential of solar energy in maritime applications.

Ammonia

Ammonia is emerging as a promising alternative fuel for shipping due to its carbon-free composition. When used as a fuel, ammonia produces no CO2 emissions, making it an attractive option for reducing the carbon footprint of the maritime industry. Ammonia can be used in internal combustion engines or in fuel cells to generate electricity for propulsion and onboard systems.

The use of ammonia as a marine fuel requires the development of specialized engines and fuel storage systems to handle its toxicity and corrosiveness. However, ongoing research and technological advancements are addressing these challenges, paving the way for the broader adoption of ammonia as a sustainable maritime fuel. Additionally, ammonia can be produced using renewable energy sources, further enhancing its environmental benefits.

By integrating wind, solar, and ammonia-based propulsion systems, the shipping industry can significantly reduce its reliance on fossil fuels and move towards more sustainable and efficient operations, contributing to a cleaner and greener future for maritime transportation.