# Analysis of a Supercapacitor/Battery Hybrid Power System for a Bulk Carrier
## 4 Results and Discussion
### Fuel Consumption and CO\({}_{2}\) Emissions  
The fuel consumption of a genset varies depending on the load factor, as shown in Figure 10, and the lowest fuel consumption is between 70%-85%. In this study, this graph was used to calculate the fuel consumption of the gensets. The emissions from fuels can be calculated by multiplying the fuel consumption of the onboard engine with the emission factor (E\({}_{\mathrm{f}}\)). This E\({}_{\mathrm{f}}\) varies according to the engine type (main and auxiliary engines, auxiliary boilers), engine rating, engine speed, type of fuel, etc. [34]. \[\text{Total emissions (kg) = Fuel consumption}\times\text{E}_{\mathrm{f}}. \tag{10}\]  
For CO\({}_{2}\) emissions, the E\({}_{\mathrm{f}}\) for each fuel type was based on IMO guidelines [36]. The E\({}_{\mathrm{f}}\) of HFO was 3.114 based on its lower calorific value of 40,200 kJ/kg and carbon content of 0.8493. The E\({}_{\mathrm{f}}\) of MGO was 3.206 based on its low calorific value of 42,700 kJ/kg and carbon content of 0.8744. And, the E\({}_{\mathrm{f}}\) of SO\({}_{\mathrm{X}}\) emissions was calculated by multiplying 0.02 with the sulfur content S (%) present in the fuel. In the case of MGO, S (%) did not exceed 0.1 %, whereas the average value of HFO was 2.7%. The E\({}_{\mathrm{f}}\) used for NO\({}_{\mathrm{X}}\) emissions was the suggested value for Tier I ships without the use of a scrubber system. These emission factors are summarized in Table 12[37]. Based on the emission factors, the emissions from onboard gensets for the conventional power system were calculated as shown in Table 13, and those for the proposed power system were calculated as shown in Table 14. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Fuel**} & \multicolumn{6}{c}{**Emission factors**} \\ \cline{2-7}  & **CO\({}_{2}\) (g-CO\({}_{2}\)/g-fuel)** & **SO\({}_{\mathrm{X}}\) (g-SO\({}_{2}\)/g-fuel)** & **NO\({}_{\mathrm{X}}\) (g-NO\({}_{\mathrm{X}}\)/g-fuel)** \\ \hline Heavy Fuel Oil (HFO) & 3.114 & 0.054 & 0.057 \\ Marine Gas Oil (MGO) & 3.206 & 0.002 & 0.057 \\ \hline \hline \end{tabular}
\end{table} 
Table 13: Emissions from onboard gensets for each mode (conventional system). Figure 10: Example of a genset fuel consumption graph [35]. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Mode**} & \multicolumn{6}{c}{**Electic Power**} & **Fuel Efficiency** & **Fuel (kg)** & **Emissions (kg)** & **NO\({}_{\mathrm{X}}\)** & **NO\({}_{\mathrm{X}}\)** \\  & **Demand (MW)** & **Time (bi)** & **(g/kWh)** & **Fuel (kg/kWh)** & **CO\({}_{2}\)** & **SO\({}_{\mathrm{X}}\)** & **NO\({}_{\mathrm{X}}\)** \\ \hline Normal seugging (10 days) & 380 & 240 & 195 & 17,784.0 & 55,379.38 & 960.34 & 1013.69 \\ \hline \multirow{4}{*}{Port in/out} & Excluding winch loads & 500 & 2[38] & & 198.0 & 634.79 & 0.40 & 11.29 \\  & Wind (Port-out) & 29.25 kWh (Table 4) & 198 & 5.8 & 18.9 & 0.01 & 0.33 \\  & Wind (Port-out) & 41.75 kWh (Table 4) & 8.3 & 26.61 & 0.02 & 0.47 \\ \hline \multirow{4}{*}{Cargo loading/unloading} & Excluding carne loads & 500 & 1201 & 12,672.0 & 40,626.43 & 25.34 & 722.30 \\  & Crane loads (\(\beta\) crimes) & 1.01 kWh \(\times\) 3 each \(\times\) & 1047.2 & 3357.32 & 2.09 & 59.69 \\  & 1800 cycle \({}^{2}\) (Table 8) & & & & & \\ \hline Harbor & 250 & 48 & 213 & 2556.0 & 8194.54 & 5.11 & 145.69 \\ \hline \multicolumn{2}{c}{**Total**} & - & **34,271.3** & **108,327.66** & **993.31** & **1953.46** \\ \hline \hline \end{tabular}
\end{table} 
Table 12: Emission factors for different pollutant types. Even though the ESS did not generate harmful emissions directly at a port, the emissions were generated indirectly, because it had to be recharged using the AMP; shore power was originally transferred from land-based power plants.