# Combination of LiCs and EDLCs with Batteries:
## 2 Proposed Hybrid Energy Storage System
### Energy Storage Implementation  
Energy storages are at the core of this research; in particular, the focus is on hybridising battery, SCs and HCs. The scale of implementation of the energy storages was small to facilitate their use in the laboratory; previous experiments have been carried out in the literature [33; 37] at a similar scale in which the load was an electronic load, as was done in this research, instead of using a physical electric vehicle. The choice of SCs and HCs was made such that they had similar capacitance such that there was room for a one-to-one comparison of both energy storages. For the experimental implementation, the SC cells used were the BCAP 3000 cells from Maxwell technologies. Each cell has a maximum voltage of 2.7 V, respectively. Six of these cells were connected in series, giving a total maximum voltage of 16.7 V and a bank capacitance of 500 F, since each cell has a cell capacitance of 3000 F. For HCs, the ESD-SCAP-CL-3000 F cells from Samwha Capacitors were used, and each cell has a maximum cell voltage of 2.8 V, which is 0.1 V higher than SC cells. Just like in the case of SCs, six cells were used in series for the HC bank to give a total of 16.8 V.  
One of the major differences between SCs and HCs is the physical sizes, as can be seen in the image in Figure 2; HC is about half the size of SC, even though being rated at the same capacitance of  
Figure 1: Overview of the concept design, highlighting the major focus areas of this research. 3000 F. This gives the feeling that HC is just a better version of SC, but looking at the internal resistances of the storage banks presented in Table 1, it is observed that SC has a lower equivalent series resistance (ESR); thus, it has a higher power density than HC, but a lower energy density. Therefore, there is an indication that SC and HC possess distinctly different characteristics that can be exploited to achieve better energy utilization. The battery used for the experimental system was a 6000-mAh 4S lithium polymer (LiPo) battery from Turnigy Power Systems(r). It is rated at a nominal voltage of 14.8 V, and usually, it is recommended not to discharge it below 14 V. The lithium polymer battery was used as opposed to the conventional use of Li-ion batteries because of the scale of the implementation. This battery has four cells in series, hence the '4S' in the name, each cell having a voltage of 3.7 V, thus amounting to 14.8 V. Table 1 presents an overview of the important electrical parameters and the corresponding values of the energy storage devices. The three energy storage devices were analysed in different combinations, which gave rise to a total of three different hybrid energy storage regimes. These regimes are as follows; battery-SC, battery-HC, and the last one, which is the main focus of this research, the battery-SC-HC energy storage regime. The characteristic values of the three different energy storage regimes were normalised based on performance and cost parameters, and these comparisons are presented in Figure 3. The data presented in Figure 3 were obtained from the datasheets of the respective energy storages, excluding the cost information. The term cost is relative and depends largely on the factors considered; therefore, for this analysis, the cost did not factor into the logistics and shipping in order to eliminate any factor