The energy transition and the decarbonization of transport dictate a switch towards electrification in the naval sector. Ferries, among the different types of ships, are those most suited for a full electrification, consisting in the replacement of engines with electric motor drives and fuel tanks with electrochemical energy storage systems. However, some cost issues and energy storage technological limitations still hamper full electrification, making partial electrification more practical, which can still be effective in reducing pollutant emissions in ports and surrounding areas. The aim of this work is to investigate some issues related to onboard energy storage systems needed for electric ferries. The Ro-Ro Elio ferry, operating in the Strait of Messina is considered as a case study. Some different solutions are investigated, in terms of economic/enviromental efficiency, which is the cost of preventing the emission of a kg of CO2.