# Analysis of Hybrid Ship Machinery System with Proton Exchange Membrane Fuel Cells and Battery Pack
## 6 Conclusions  
The research has shown repowering an existing vessel with a PEMFC-battery hybrid power system increased efficiency and eliminated greenhouse gas emissions compared to the previously installed diesel propulsion system. The new numerical model of the hybrid power system was developed and can be used for different hybrid systems and power demand optimization and as a very flexible system for implementation in any electric-dependent power facility with different applications. The model will be further developed for BoP optimization in realistic cycles of operation. For further development of the numerical model, an intended improvement would be a system with different output power of the PEMFC stack or a combination of one main and another auxiliary PEMFC stack and the implementation of photovoltaics with detailed insight into their power production and potential to additionally reduce the requirement for batteries and increase possibilities for the implementation of this numerical model. Results have shown that the system using the PEMFC stack with battery system requires a significantly smaller amount of fuel, namely 18.68% of fuel by mass in comparison to the previous system (284.7 kg of hydrogen in comparison to 1524 kg of diesel), which is emission-free and offers high flexibility for further system upgrades, as such a system generates electricity, and additional components can be added without the necessity of additional complex refitting. The total efficiency of the PEMFC system is around 60% [29] in comparison to diesel engines that have a maximal efficiency around 45% for systems with similar power.  
There are many ways to further improve this system with additional implementation of an auxiliary PEMFC stack, with which the required power of batteries would be reduced,  
Figure 10: SoC and propeller speed for reduced size of battery package and activated hysteresis mechanism.  
such as photovoltaic (PV) collectors for electricity production, as this vessel has a large unused area on deck, and the area of the voyage has very good conditions for such energy production. This system would have the potential for generation of around 48 kWp of electricity, as the deck area is around 240 m\({}^{2}\) (about 5 m\({}^{2}\) for 1 kWp), which would dramatically reduce electricity consumption from the batteries during the voyage and improve charging speed, as the maximum current of charging is 600 A, and there is 100 A deficiency of charging, as the PEMFC stack has a maximal current of 500 A. Additionally, the implementation of charging from the grid in port would significantly reduce consumption of hydrogen (around 87.48 kg), as the load of the PEMFC stack during the time in port can be removed, and the speed of charging can be set to 600 A.  
Conceptualization, J.P. and T.V.; data curation, J.P., T.V. and G.R.; formal analysis, J.P. and T.V.; funding acquisition, G.R.; investigation, J.P., T.V. and G.R.; methodology, J.P., T.V., G.R. and Z.P.; project administration, G.R. and Z.P.; software, J.P. and T.V.; supervision, G.R. and Z.P.; validation, J.P., T.V., G.R. and Z.P.; visualization, J.P. and T.V.; writing--original draft, J.P. and T.V.; writing--review and editing, J.P., T.V., G.R. and Z.P. All authors have read and agreed to the published version of the manuscript.  
This work has been fully supported by the Croatian Science Foundation under the project IP:2020-02-6249.  
Not applicable.  
The data presented in this study are available in article.  
The authors declare no conflicts of interest.