Wind has been the source of power for ships since ages. Today it has gained renewed interest by the shipping community to provide a solution to reduce emissions. It will not be possible to provide all the required power by a wind device, but it is possible to use wind as a supporting source of power in combination with a combustion engine.
The wind technologies available today are not all new inventions. There are systems that are used onboard modern yachts like rigid winged sails and dynarigs, but also kites and flettner rotors are promising to use onboard commercial vessels. Practical experience exists with two of these methods, which are currently in use: kites, and the Flettner rotor. In a recent design the DynaRig principle is being used for the ecoliner concept. There are obviously no direct fuel costs involved in using wind to propel a ship. Most wind-assisted propulsion systems require a secondary source of energy to be operated:
- Flettner rotors need to be started up by motors to develop their aerodynamic thrust forces.
- Soft and solid sail systems require a certain amount of energy for hoisting and dropping as well as for position adjustments to achieve the optimum angle of attack.
- Kites need to be launched, inflated, controlled and retracted by external means.
There is no infrastructure required to make use of wind as an energy source. Specialized knowledge may be required for maintenance and repair work, most of which may not be possible on board. Depending on the size of an installed wind propulsion system, there may be restrictions for passing under bridges. In addition, certain types of wind assistance systems may cause some problems loading and unloading the ship.
Wind as a power source is unlimited. However, the quantity and quality of this energy source is not constant. As a meteorological phenomenon, the strength and direction of wind is subject to frequent change. Global trade routes with relatively constant, high wind conditions are best suited for profitable use of this energy source, especially when combined with weather routing based on global weather patterns and local forecasts. So for commercial operated ships it is not possible to solely rely on wind as a power source.
A wind propulsion system can reduce fuel consumption. The energy savings achieved are directly proportionate to the reduction of fuel-related CO2, NOX, SOX, particulate matter (PM) and other emissions. The range of reduction depends on the trade route of the ship and the weather conditions. For some cases it can also have a negative impact.
Photovoltaic cells can offer an addition to the electric power supply of a ship. However, the maximum contribution is small when compared with the power required to drive the ship. It is important to take into account that not everywhere on earth the available solar power is the same. This is highly dependent on weather conditions and place on the earth.
To install solar panels onboard a ship it is important that there is a large deck surface area on the ship which does not interfere with cargo handling or other purposes for which the ship was designed. The shipe that suits this requirement the most are car transporters. Resulting from the laws of physics, this technology inherently suffers from low generation capability, even if efficiency could be improved to 100%.
As such, coupled with a maximum attainable specific power from the sun at given global locations and the generally limited available deck area suggest that the power attainable would only be sufficient to augment the auxiliary power demands.
As a general conclusion on renewables we a clear distinction needs to be made between the production and use of renewable energy on board the ship itself and the use of renewable energy from land through electronic fuels). Both options have their merrits. It seems that production of e-fuels can be done in a more efficient and cost effective way in comparison with renewable energy production onboard a ship. The renewable energy produced on land can be used to provide the shipping industry with energy. This can be in different forms. It can be as electricty in batteries for inland use on small ferries or it can be as hydrogen or methanol for exampleto be used on ocean going vessels.
-Assessment of selected alternative fuels and technologies (DNV GL) 2018