# Combination of LiCs and EDLCs with Batteries:
## 2 Proposed Hybrid Energy Storage System
### Energy Storage Implementation
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Device** & **Parameter** & **Value** \\ \hline \multirow{5}{*}{SC (Maxwell Technologies BCAP3000) [38]} & Cell internal resistance & 0.29 m\(\Omega\) \\  & (Bank internal resistance) & (1.74 m\(\Omega\)) \\ \cline{2-3}  & Cell voltage & 2.7 V \\  & (Max. bank voltage) & (16.2 V) \\ \cline{2-3}  & Cell capacitance & 3000 F \\  & (Bank capacitance) & (500 F) \\ \hline \multirow{5}{*}{HC (Samwha capacitor ESD-SCAP CL 3000 F) [39]} & Cell internal resistance & 0.55 m\(\Omega\) \\  & (Bank internal resistance) & (3.3 m\(\Omega\)) \\ \cline{2-3}  & Cell voltage & 2.8 V \\ \cline{2-3}  & (Max. bank voltage) & (16.8 V) \\ \cline{2-3}  & Cell capacitance & 3000 F \\ \cline{2-3}  & (Bank capacitance) & (500 F) \\ \hline \multirow{3}{*}{Battery (Turnigy nano-tech Li-Po 6.0 Battery) [40]} & Rated voltage & 14.8 V \\ \cline{2-3}  & Capacity & 6000 mAh \\ \cline{1-1} \cline{2-3}  & Internal resistance & 12 m\(\Omega\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Electrical characteristics of the battery, SC, and HC used for the experimental implementation. Figure 2: Comparison of the physical sizes of the supercapacitor (SC) and hybrid capacitor (HC) banks. that could skew the results in any direction; only the market prices of the devices were considered. Furthermore, the cost did not factor in depreciation or the cost of any associated accessories; therefore, only the replacement costs are considered. The performance classification of energy storages and even energy sources is usually into two categories: the volume and mass characteristics of the energy storages. The volume characteristics are taken seriously when considering applications that do not necessarily require mobility; an example of such applications is in grid-scale energy storages, in most cases, the mass of the energy storage is not much of a concern in such applications. However, in automotive applications such as EVs, the mass of the energy storage is of equal importance as the volume of space it would occupy. The volume characteristic of the energy storages can be further classified into two, namely the power and the energy density, while the weight characteristic is further classified as specific power and specific energy. The power density is the time rate of energy transfer per unit volume, while the energy density is the amount of energy stored in a system per unit volume. On the other hand, the specific power is the time rate of energy transfer per unit mass, while the specific energy is the amount of energy stored in a system per unit mass. In Figure 3, it can be observed that the highest power density is obtained with the energy storage regime that has the combination of the battery, SC, and HC at 12.59 kW/kg, and 17.16 MW/m\({}^{3}\) for the specific power and power density, respectively. In the battery-SC-HC hybrid storage, the ratio of power to energy is also at the lowest at 1:1.3; this is an improvement from the 1:3 and 1:5 of the battery-HC and battery-SC hybrid energy storage systems, respectively. For the economic implications, the combination of all three energy storages has the lowest cost per unit power sitting at 14.81 $/kW; its cost per unit energy is about 11 $/Wh; which is higher than that of the battery-SC at 6.6 $/Wh and the battery-HC at 8.47 $/Wh. However, looking at the ratio of the cost of energy to the cost of power per unit, the battery-SC-HC hybrid energy storage system is the lowest at 1:1.3 when compared to 1:3 and 1:5 of the battery-SC and battery-HC energy storage systems, respectively; thus making it a very cost-attractive hybridisation or combination of the energy storages. It is expected that as the years go by, the cost of HCs will drop further, which would further contribute positively to the benefits of having both SCs and HCs in the same energy storage system.