## Appendix B Detailed Results of the Trade Study on Energy Conversion and Energy Storage Subsystems  
### Calculation Approach for the Trade Study  
The SailREC System is approximated and calculations are performed using spreadsheets. The flow charts (cf. Figures 5 and 11) give a schematic representation of the processes and associated costs that are used in the calculations. In the flow charts, the blocks that are filled white (i.e., blocks for electrical energy that is sourced from the turbine, electroly for generation of hydrogen, onboard storage, etc.) are the ones that are common for all the four fuel options, while the respective efficiencies and costs may still differ. The blocks with a colour fill of blue are the stages which are primarily different from those of others (i.e., liquefier, compressor, Haber-Bosch process, and methanol synthesis). The losses that occur at corresponding stages are indicated by arrows on top of them. The blocks with a grey filling and rounded edges (i.e., desalination, DAC, and PSA) are stages required in the SailREC System but are not exactly used in the calculations as a subsystem. The text in red fonts also shows the differences between the options. The general idea used in the calculation is to compute the efficiency of each block, which represents a relevant stage or component in the chain. If CAPEX is considered, it is represented with a red $ sign, while for OPEX it is a green one. There are certain losses in the blocks, which are taken into account to get the efficiency of the blocks. Finally, the overall efficiency is calculated as the product of all the single block's efficiencies. This is multiplied by the electrical power from the wind turbine to obtain the total energy that is realised each year. The costs and the energy calculated are used to get the LCOE of each flow chain. Another parameter used for assessing the options in the trade study is the measure of hull volume that will be required. Here, only the mass of fuel harvested at the end of the loading cycle and the mass of the tank used to store it are considered, and the equivalent volume of water to be displaced is determined. The main assumptions made in the calculation approach are listed in the following:  
* The wall thickness calculation for the tanks (for storage and transportation) leans towards the ASME Boiler and Pressure Vessel Code [48; 49]. * The shape of the tanks is assumed to be a cylinder.--Use of spherical tanks could be better as their volume to surface area ratio is higher, reducing the losses due to heating. They are also stronger than cylindrical tanks with the same wall thickness. However, the spherical tanks are costlier to manufacture [50]. * The tank material is stainless steel except for gaseous hydrogen, for which carbon fiber is used.--Another method could be the use of a stack of gas bottles, each having a smaller diameter, if only materials of lower allowable stress can be used. Only material costs are considered for tank CAPEX. * The cooling loss of fuels that are not stored at ambient temperature is calculated as the heat energy flowing into the storage tank. In the case of liquid hydrogen and ammonia, they need to be stored in so-called Dewar tanks--double-layered tanks where there is a vacuum maintained between the layers. * Thermal radiation is only considered as a source of heat inflow (cf. Figure 11). The top and bottom flat surfaces are not considered in the modelling. The view factor is estimated according to the radiation between two concentric cylinders of a finite length according to VDI e.V. [51]. * The required energy for transport till port through the sea and on land from port till plant with a truck is taken into account.--Other ways of transporting the fuel, such as pipelines, rail transport, etc., can be modelled in further studies. There is a major push in the direction of the development of hydrogen transport infrastructure such as the hydrogen grid [52].