This master thesis aims to conduct energy management system (EMS) optimization to minimize the total cost of a zero-emission vessel with a hybrid power system.
As the International Maritime Organisation (IMO) agreed to reduce greenhouse gases (GHG) by the sector by 50% by 2050, the importance of alternative fuels is getting bigger. To comply with the regulation and movements towards reducing carbon dioxide (CO2) and Nitrogen oxide (NOx) emissions, various investigation on the technology has been done. Fuel cells and batteries, for instance, are promising energy sources that do not emit those emissions.
The fuel cell has high energy density but is not sufficient to manage dynamic power fluctuation. On the other hand, the battery not only has the advantage of having the high power density that the fuel cell is lack of, but also can react with fast speed to massive power fluctuation. Therefore, the combination of fuel cells and batteries can be a good option as a hybrid power system for zero-emission vessels.
However, there is still a huge obstacle which is the relatively short lifetime of fuel cells. Since the short lifetime increases maintenance and replacement costs during vessel operation, its stable but efficient performance is much more essential for the hybrid power system. A battery, furthermore, also has a state of charge (SOC) rate that affects its degradation. As a result, the management of these energy sources is the key factor for the vessel operation to minimize costs and the EMS should be optimized.
The optimization is carried out by MATLAB and an optimization algorithm called YALMIP and a solver CPLEX will be used. By linearizing non-linear constraints, the mixed-integer linear programming (MILP) method shall be applied. Prior to the optimization, a literature investigation for zero-emission energy sources and high-level control systems including the energy management system (EMS), power management system (PMS), and battery management system (BMS) will be done.
The optimization results are firstly compared to the result that has a rule-based strategy as a benchmark case. Furthermore, since the application of the hybrid power system is to comply with regulations by IMO, the same load profile is implemented with a conventional engine system run by marine diesel oil (MDO) to compare the total cost. CO2 and NOx taxes are imposed for the case with MDO fuel. This comparison has evaluated the optimization results and calculated savings by avoiding emissions.
The fuel cell technology is still immature, so the optimization result has shown that the hybrid power system is 15% more expensive compared to the diesel engines with the current price level. However, when the fuel cell system is to be 25% cheaper by 2030 at the earliest, 13% of life cycle cost reduction is anticipated. Considering the penalty toward GHG emissions will be increased continuously, it is obvious that the hybrid power system with fuel cells and batteries is a promising alternative for the zero-emission era.