## 3 Results
### FC/Renewable Hybrid Power System  
#### 3.2.1 Fuel Consumption  
The behavior of the FC/renewable HPS using the strategies sFF, air-PFC, fuel-PFC, and air/fuel-PFC are presented in Figures 10-13 under the same load profile (see the 1 st plot), but using the profile of renewable energy presented in Figure 2 and is seen here in the 2 nd plot.  
Figure 11: FC/renewable HPS behavior using the air-PFC strategy.  
Figure 12: FC/renewable HPS behavior using the fuel-PFC strategy.  
It can be seen that the structure of the plots in Figures 10-13 are the same as that of Figures 4-7, with the exception of adding RES power in the 2 nd plot, being as follows: the 1 st plot shows the DC load profile; the 2 nd plot, RES power; the 3 rd plot, OER; the 4 th plot, ESS power; the 5 th and 6 th plots, \(AirFr\) and \(FuelFr\), respectively; the 7 th plot, \(Fuel_{T}\); the 8 th plot, \(Fuel_{eff}\); and the 9 th plot, \(\eta_{sys}=P_{FCnet}/P_{FC}\). The OER of the FC/renewable HPS under all strategies varies in a large range (from 2.3 to 7) compared to the OER of the FC system (from 2.3 to 4), but it still is under recommended limits (see the 3 rd plot).  
It can be seen that \(P_{ESS}\) still varies around zero but is noisy due to the random part added to renewable energy (see the 4 th plot), thus validating the charge-sustaining mode of the battery in the case of FC/renewable HPS.  
The power profile \(P_{Load}-P_{RES}>0\) is followed by the both \(AirFr\) and \(FuelFr\) in the sFF strategy, by \(AirFr\) and \(FuelFr\) in the strategies air-PFC and fuel-PFC respectively, and by \(FuelFr\) and then by \(AirFr\) in the air/fuel-PFC switching strategy (see plots 5 and 6). If \(P_{RES}-P_{Load}>0\), then the FC system operates in standby mode, and the excess of power (\(P_{RES}-P_{Load}\)) will supply an electrolyzer to produce hydrogen.  
The fuel consumption of the FC system using the strategies sFF, air-PFC, fuel-PFC and air/fuel-PFC is mentioned in Table 3 (see the 7 th plot). The last two plots show the values of the performance indicators \(Fuel_{eff}\) and \(\eta_{sys}\). It should be noted that the values of \(Fuel_{eff}\) and \(\eta_{sys}\) are lower due to the standby mode of the FC system operation in the case where RES power exceeds the load demand (\(P_{RES}>P_{Load}\)).  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \(Fuel_{T(AirFuel-PFC)}^{Renewable}\) & \(Fuel_{T(Air-PFC)}^{Renewable}\) & \(Fuel_{T(Fuel-PFC)}^{Renewable}\) & \(Fuel_{T(sFF)}^{Renewable}\) \\ \hline
107 L & 115.4 L & 116.6 L & 123.6 L \\ \hline \hline \end{tabular}
\end{table}
Table 3: Fuel consumption of FC/renewable HPS using the strategies sFF, air-PFC, fuel-PFC, and air/fuel-PFC.  
Figure 13: FC/renewable HPS behavior using air/fuel-PFC strategy.  
The fuel economy of the strategy air/fuel-PFC compared to the strategies sFF, air-PFC, and fuel-PFC is estimated in Table 4 using (16):  
\[\% Fuel_{T(sFF)}^{Renewable}=100\left(\frac{ Fuel_{T(sFF)}^{Renewable}- Fuel_{T(Air/Fud-PFC)}^{Renewable}}{ Fuel_{T(sFF)}^{Renewable}}\right) \tag{16a}\]  
\[\% Fuel_{T(Air-PFC)}^{Renewable}=100\left(\frac{ Fuel_{T(Air-PFC)}^{Renewable}- Fuel_{T(Air/Fud-PFC)}^{Renewable}}{ Fuel_{T(Air-PFC)}^{Renewable}}\right) \tag{16b}\]  
\[\% Fuel_{T(Fud-PFC)}^{Renewable}=100\left(\frac{ Fuel_{T(Fud-PFC)}^{Renewable}- Fuel_{T(Air/Fud-PFC)}^{Renewable}}{ Fuel_{T(Fud-PFC)}^{Renewable}}\right) \tag{16c}\]