*5.2. Space and Operational Cost*

Figure 14 illustrates the volume for storage of the fuel and liquefied CO2 along with the cost of fuels for the methane-based and methanol-based systems, which are required for 475 kW of net electricity generation during the total navigation time. A specific fuel cost of 9.76 USD/mmBtu for LNG [72] and 26.08 USD/mmBtu [73] for methanol are used, and both are the average cost in 2018 in the references. The result shows that that methane-based system requires 43.69 m<sup>3</sup> for LNG storage and 32.30 m<sup>3</sup> for the liquefied CO2 storage, whereas the methanol-based system requires 48.03 m<sup>3</sup> for methanol and 36.17 m<sup>3</sup> for the liquefied CO2. Accordingly, the methanol-based system needs approximately 1.1 times the volume (equivalent to 8 m<sup>3</sup> more) for fuel and liquefied CO2 storage. In other words, the methanol-based system consumes a higher amount of methanol as fuel and generate a higher amount of CO2. Regarding the fuel cost, the methanol-based system has a 2.2 times higher fuel cost than the methane-based system for 475 kW of net electricity generation during the total navigation time. Therefore, the methane-based system is more competitive than the methanol-based system from the economic point of view, when only the fuel cost and volume are taken into account. However, note that the overall investment cost for both systems, which is beyond the scope of the current study, may also be an important factor in the selection of system.

**Figure 14.** Fuel volumes and cost of methane-based and methanol-based systems for 475 kW of net electricity generation during the total navigation time.
