**5. The contribution of an energy storage device for charging EVs**

It is estimated that over the next 15 years there will be more than a million electric vehicles in a small country as Thailand [66]. To reach this target both government and business sectors must provide infrastructure and technologies corresponding to technology for electric power supply within vehicles and electric vehicle charging station technology. Currently Thailand has 400 electric vehicle charging stations nationwide [67]. The acquisition of electric energy supplied for charging an electric vehicle is to connect a charging system through a meter to a transformer. If the EV demand grows significantly the share of electricity consumption from industrial and household sectors will be a serious issue. The EV driven 311 km requires approximately 40 kWh of energy which costs approximately 200 THB (\$6.40) [68]. Thinking about 10,760,499 EVs in Bangkok, 430 million kWh, worth 2152 million baht per charge will be a requirement [69]. Using renewable energy sources to generate electricity for the charging system should give a positive effect on the country's energy security. Furthermore, an energy storage is needed for the integrated alternative electricity generation. The part aim to emphasize the information related to applying redox flow battery for the integrated charging system. Redox flow battery is considered as the most promising candidate in terms of its unlimited capacity, flexible security design and fast-response [70, 71]. In 2025, the forecast of rechargeable battery in the world expects to increase flow batteries using from 0.4% to 6.6%. Interesting properties of redox flow batteries are 85% of efficiency, 13,000 of cycle life, and 5–80 \$/MWh∙cycles of capital cost. The major costs of the redox flow battery are electrolyte solution at 37% and stack cell at 31% [72] (**Table 2**).

The priority performance of battery can be considered as following data. **Top power:** Flow batteries > Lead acid > Li-ion > Electrolyzer. The power of flow battery is defined by the size and number of cells. **Top energy:** Flow batteries > Li-ion > Electrolyzer > Lead acid.

The energetic capacity is set by the amount of electrolyte stored in the reservoirs.

**Discharge time:** Flow battery > Electrolyzer > Lithium ion = Lead acid. **Round trip efficiency:** Li-ion > Flow batteries > Lead acid > Electrolyzer. **Cycle life:** Electrolyzer > Flow batteries > Li-ion > Lead acid.

**Capital cost (\$/MWh∙cycles):** Electrolyzer > Li-ion > Lead acid > Flow batteries.


#### *Hydrogen Fuel Cell Implementation for the Transportation Sector DOI: http://dx.doi.org/10.5772/intechopen.95291*

#### **Table 2.**

*Performance of energy storage devices [72].*

A conventionally single cell of the redox flow battery system consists of two external tanks storing electrolytes, electrodes both anode and cathode sides, a membrane separator, and pumps to generate circulation system. In a discharging process, the anolyte solution is fed in the anode side by the pump and electrolyte flow on bipolar. The electrolyte diffuses through the electrode and it occurs oxidation reaction creating electrons. The electrons move back from an electrode to a bipolar plate and take path around an electrical circuit from the anode side to cathode side. The charge-carrying species directly transfer from the anode to the cathode passing the ion-exchange membrane separating the anolyte and catholyte solution. The catholyte solution is fed in the cathode side, flows on the bipolar plate, and flows via a porous electrode occurring a reduction reaction where catholyte combines with the electron and proton. Once the flow battery is charged, a reduction takes place in the anolyte, while an oxidation is in the catholyte (**Figure 11**) [73, 74].

There are rational decisions for using redox flow battery as a generator in charging station as following examples. People mainly recharge vehicles between 7:00 to 9:00 am, and between 18:00 and 20:00 pm. Grid operators would not be capable to suppress peak power requirements without critically oversizing installed power. Supplement a battery to a fast charging station is a feasible approach to alleviate the oversizing installed power. This electric storage system acts as a buffer to decrease the peak power request on the network without increasing EV charging time [75]. In this situation, the redox flow battery charges installed power during low electricity demand periods to supply electricity for the fast charging. The redox flow battery possesses specific characteristics; ability to decouple rated power from rated capacity, good design flexibility, and nearly unrestricted life. Additionally, the liquid electrolyte contained in the redox flow battery system allowing their installation inside deactivated underground gas container located at gas stations. This installation method authorizes a transition of a conventional gas station to a commercial charging station [76, 77].

#### **Figure 11.** *The schematic diagram of a redox flow battery.*

#### **Figure 12.**

*(A) the overall process of electricity production initiated by a wind turbine. (B) the overall process of electricity generation initiated by a solar cell [79].*

In terms of research related to a scaled-up vanadium redox flow battery for HEVs [78], it rapidly charged by electrolyte replacement making it attractive for charging EVs or HEVs. In the not so distant future, redox flow batteries will be useful for EVs, forklift truck, and golf-cart. EVs used for long journey distance may be conceivable if the infrastructure is in place. PEMFC can be another option for charging station when integrated system as primarily renewable source/electrolyzer/PEMFC is constructed. According to these two systems, the wind/PEM electrolyzer/ compressed hydrogen/PEMFC (**Figure 12 (A)**) generates 688.57 W of power. This generated power is significantly higher than the produced power of solar/PEM electrolyzer/ compressed hydrogen/PEMFC (262.37 W) (**Figure 12 (B)**).

*Hydrogen Fuel Cell Implementation for the Transportation Sector DOI: http://dx.doi.org/10.5772/intechopen.95291*
