TOPSIS MCDM approach for the comparison of traditional and innovative ship propulsion systems

Innovative propulsion systems are today under the spotlights because of their potential to reduce pollutant emissions enabling the sustainable mobility in naval transportation. Hybrid and electric propulsion systems require the battery size to be optimized in order to satisfy both the vessel’s load profile and the need to keep under control the weight/volume occupied by the battery pack. Our previous work focused on determining the optimal battery size for electric and hybrid propulsion systems that minimize the management cost per unit time, based on the load profile. However, information related to the emissions generated by the hybrid and endothermic systems, nor the weight/volume occupied by the battery pack were considered. Based on the results of the previous work, this paper aims at assessing how factors like battery weight/volume and CO2 emissions impact on the overall technical feasibility of the hybrid/electric ship propulsion systems. The approach here used consists in comparing endothermic, hybrid and electric solutions using the TOPSIS MCDM method to rank the alternatives. Five criteria, namely ‘CO2 emissions’, ‘Energy consumed’, ‘Fuel consumed’, ‘Weight (fuel and/or battery), ‘Management cost per unit time’ were selected. Setting first the same weight for all criteria, the results showed that endothermic systems are to be preferred to electric systems, while the hybrid solutions are dominated by the two others. The sensitivity analysis on the criteria weights evidenced the superiority of electric propulsion systems when the importance of the criteria ‘CO2 emissions’ and ‘Fuel consumed’ increases and the importance of the criterion ‘Energy consumed’ decreases.