# Analysis of a Supercapacitor/Battery Hybrid Power System for a Bulk Carrier
## 4 Results and Discussion
### Fuel Consumption and CO\({}_{2}\) Emissions
Thus, the generated emissions from the used shore power were calculated as shown in Table 15. In this study, emission factors that generated 1 kWh of electricity were assumed to be 151 g-CO\({}_{2}\)/kWh, 0.03 g-SO\({}_{\text{X}}\)/kWh, and 0.16 g-NO\({}_{\text{X}}\)/kWh based on a European electricity company [40]. This value changed depending on the country. For example, in Denmark where the dominant electricity power source is from wind power plants (about 44%, 2016) [41], the total CO\({}_{2}\) emission factor is 75 g/kWh, whereas the world average is 507 g/kWh [42]. Overall, the proposed system could reduce CO\({}_{2}\), SO\({}_{\text{X}}\), and NO\({}_{\text{X}}\) emissions, especially in the cargo handling and harbor modes at a port (Figure 11c,d). There was about a 77% reduction for CO\({}_{2}\), about a 93% reduction for SO\({}_{\text{X}}\), and a 99% reduction for NO\({}_{\text{X}}\). On the contrary, the emission reduction rates for the normal seagoing mode (Figure 11a) and the port in/out mode (Figure 11b) were not high (under 10%). In addition, the emission reduction rate varied depending on the ship's schedule. As shown in Table 16, when the cargo handling time was 60 h, the emission reduction rate was approximately 28% for CO\({}_{2}\), 4% for SO\({}_{\text{X}}\), and 35% for NOx, but this increased to 45%, 6%, and 56% each for 180 h of long cargo handling operations. And, as shown in Table 17, when the sailing time was 20 d, the emission reduction rate was approximately 26% for CO\({}_{2}\), 4% for SO\({}_{\text{X}}\), and 32% for NOx, but this increased to 50%, 8%, and 64% each for 5 d of short sailing time. Therefore, the proposed system is more eco-friendly if a ship has a long cargo handling time or visits many ports with a short-term sailing time. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Cargo Handling Time at a Port (h) t\({}^{1}\)**} & \multirow{2}{*}{\begin{tabular}{c} **Conventional System (ton/yr)** \\ **CO\({}_{2}\)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **SO\({}_{\text{X}}\)** \\ **SO\({}_{\text{X}}\)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **NO\({}_{\text{X}}\)** \\ **CO\({}_{2}\)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **CO\({}_{2}\)** \\ **SO\({}_{\text{X}}\)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **SO\({}_{\text{X}}\)** \\ **CO\({}_{2}\)** \\ \end{tabular} } & \multirow{2}{*}{\
\begin{tabular}{c} **SO\({}_{\text{X}}\)** \\ **SO\({}_{\text{X}}\)** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **NO\({}_{\text{X}}\)** \\ **CO\({}_{2}\)** \\ \end{tabular} } \\ \hline
60 & 1724.91 & 19.59 & 31.25 & 1237.33 & 18.86 & 20.23 & 28.27 & 3.73 & 35.26 \\
90 & 1944.83 & 19.73 & 35.16 & 1289.03 & 18.87 & 20.29 & 33.72 & 4.36 & 42.29 \\
120 & 2164.75 & 19.87 & 39.07 & 1340.72 & 18.88 & 20.34 & 38.07 & 4.98 & 47.94 \\
150 & 2384.67 & 20.00 & 42.98 & 1392.41 & 18.89 & 20.40 & 41.61 & 5.55 & 52.54 \\
180 & 2604.59 & 20.14 & 46.89 & 1444.11 & 18.90 & 20.45 & 44.56 & 6.16 & 56.39 \\ \hline \hline \end{tabular}  
* Assuming that the ship visits 20 ports per year with a sailing time of 10 d.  
\end{table} 
Table 16: Comparison of emissions according to different cargo handling times. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{ \begin{tabular}{c} **Mode** \\ **Code** \\ \end{tabular}  } & \multirow{2}{*}{ \begin{tabular}{c} **Electric Power Demand (kW)** \\ \end{tabular}  } & \multirow{2}{*}{**Time (h)**} & \multirow{2}{*}{ \begin{tabular}{c} **Fuel Efficiency** \\ **(g/kWh)** \\ \end{tabular}  } & \multirow{2}{*}{ \begin{tabular}{c} **Fuel (kg)** \\ \end{tabular}  } & \multirow{2}{*}{ \begin{tabular}{c} **Emissions (kg)** \\ **CO\({}_{2}\)** \\ \end{tabular}  } & \multirow{2}{*}{ \begin{tabular}{c} **SO\({}_{\text{X}}\)** \\ **SO\({}_{\text{X}}\)** \\ \end{tabular}  } & \multirow{2}{*}{ \begin{tabular}{c} **NO\({}_{\text{X}}\)** \\ **NO\({}_{\text{X}}\)** \\ \end{tabular}  } \\ \hline \multirow{4}{*}{