Comparative study of energy efficiency and cost optimization in low-emission marine power systems with alternative fuels

Marine hybrid power systems fed by so-called "alternative fuels" are key enablers to reducing greenhouse gas emissions from ship propulsion and reaching international targets, particularly for large vessels. In this paper, a few scenarios of green propulsion are studied based on low-emission energy carriers, marine batteries, and all-electric power architecture. A cost model is proposed to optimise the power system via minimising the fuel consumption and hence, the operational expenses (OPEX). The proposed cost model includes the different types of fuels and a battery cycling and battery energy dissipation term. The result is an optimal energy management system (EMS) based on mixed-integer linear programming (MILP) formulation that is tuned for alternative fuel. The optimised EMS is tested on a commercial LNG vessel, and it enables a more stable use of generators. However, as the paper reveals, optimised control strategies will not yield practical results in reaching international emission targets. Hence, alternative fuels will be pivotal in reducing emissions from shipping.