## 4 Vehicle Applications of Supercapacitors
### Fuel Cell Vehicles (FCV) Using Supercapacitors  
Fuel cell vehicles are hybrid-electric vehicles using a battery to assist the fuel cell during periods of high-power demand and to recovery energy during vehicle braking. As in HEVs, supercapacitors can replace the power battery. The supercapacitors are more efficient than the battery, especially during regenerative braking in large vehicles. Advisor simulations using fuel cells [20; 21] were run for some of the same vehicles as were evaluated under the HEVs category. The fuel cell efficiency used in the simulations was 60%. The results of the simulations are shown in Table 9. In general, the vehicles using supercapacitors had slightly higher equivalent fuel economy than the corresponding vehicle  
Figure 5: PHEVs using the 4.1 V supercapacitors on urban driving cycles. using a battery. As found in [20,21], the effect of hybridization on fuel consumption using fuel cells is smaller than in vehicles using engines. Note from Table 9 that the advanced Aowei supercapacitors are also smaller and lighter than the lithium battery they can replace. The advantage of the supercapacitors in terms of increasing the fuel economy decreases for larger vehicles that require higher power from the fuel cell. However, in larger vehicles, the advantage in size of the supercapacitor compared to the battery is greater. To a good approximation, the hydrogen consumption is  
\[\text{kgH2/mi}=1/\text{mpgG}\text{ equivalent} \tag{7}\]  
Advisor output graphics are shown in Figure 6 for several types of vehicles using fuel cells. As was the case with hybrid vehicles using engines, there has been very little published data on the use of supercapacitors in fuel cell vehicles in recent years. Both Honda and Hyundai used supercapacitors in their early development of fuel cell vehicles [22,23], but both switched to lithium batteries in their later developments. However, there have been many analyses performed on fuel cell systems that show supercapacitors will function well in fuel cell systems [24,25]. In addition, there have been many laboratory studies of supercapacitors with fuel cells that show that supercapacitors and fuel cells are very compatible [26,27]. Hence, with the large increase in the energy density, and the related expected large reduction in cost (USD/kWh), of supercapacitors, they should be seriously considered for fuel cell hybrid vehicle applications. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & **kg** & **L** & **Wh** & **EM kW** & **Mpg * FUDS** & **Mpg * Highway** & **Efficiency \%** \\ \hline
**Mid-size car** & & & & & 34.7 & 46 & \\ ICE gasoline & & & & & 107 & 95.9 & 91 \\ Lithium battery & 28 & 11.2 & 4508 & 160 & 107 & 95.9 & 97 \\ EDLC Skeleton & 34 & 24.3 & 279 & & 113.5 & 96.9 & 97 \\ Aowei 3.8 V & 18 & 12.9 & 720 & & 108.3 & 95.7 & 94 \\ Aowei 4.1 V & 12 & 8.6 & 780 & & 109.9 & 95 & 95 (1/2R) \\
**small SUV** & & & & & 35.3 & 44.7 & \\ ICE gasoline & & & & & 85.2 & 77.3 & 87 \\ Lithium battery & 25 & 10 & 4025 & 160 & 85.2 & 77.3 & 87 \\ EDLC Skeleton & 34 & 24 & 279 & & 95.3 & 77.9 & 97 \\ Aowei 3.8 V & 13 & 9.3 & 520 & & 90.6 & 76.5 & 93 \\ Aowei 4.1 V & 10 & 7.1 & 650 & & 92.5 & 77.3 & 95 (1/2R) \\
**Delivery van** & & & & & 12.8 & 12.7 & \\ ICE diesel & & & & & 12.8 & 12.7 & \\ Lithium battery & 53 & 21.2 & 8533 & 200 & 27.9 & 22.5 & 86 \\ EDLC Skeleton & 43 & 30.7 & 353 & & 29.4 & 22.6 & 94 \\ Aowei 3.8 V & 35 & 25 & 1400 & & 28.5 & 22.6 & 991 \\ Aowei 4.1 V & 25 & 17.9 & 1625 & & 28.7 & 22.6 & 94 (1/2R) \\
**Long haul truck** & & & & & 4.0 & 6.9 & \\ ICE Diesel & & & & & 4.0 & 6.9 & \\ Lithium battery & 169 & 68 & 21,735 & 350 & 6.4 & 10.5 & 85 \\ EDLC Skeleton & 135 & 96 & 935 & & 6.7 & 10.5 & 97 \\ Aowei 3.8 V & 86 & 61 & 2960 & & 6.5 & 10.5 & 94 \\ Aowei 4.1 V & 52 & 37 & 2860 & & 6.6 & 10.5 & 93 (1/2 R) \\ \hline \hline \end{tabular}  
* Fuel cell efficiency 60%.  
\end{table} 
Table 9: Summary of the Advisor fuel cell simulation results and key inputs. Figure 6: Fuel cell vehicles using the 4.1 V supercapacitors on urban driving cycles.