The chemical energy is converted to the electric energy when the electrolytes flow through the external tanks. The volume of the electrolyte and the surface area of the electrode influence the performance of the flow battery. Flow batteries can be employed both as a rechargeable secondary battery and a fuel cell.
In contrast with conventional batteries, flow batteries store energy in the electrolyte solutions. Therefore, the power and energy ratings are independent, the storage capacity being determined by the quantity of electrolyte used and the power rating determined by the active area of the cell stack.
A typical flow battery has been shown in Fig. 8. Some of the main characteristics of flow batteries are high power, long duration, and power rating and the energy rating are decoupled; electrolytes can be replaced easily . Fig. 8. Illustration of flow battery system [133,137]. Zhibin Zhou, ...
Since capacity is independent of the power-generating component, as in an internal combustion engine and gas tank, it can be increased by simple enlargement of the electrolyte storage tanks. Flow batteries allow for independent scaleup of power and capacity specifications since the chemical species are stored outside the cell.
Also, note that as the volume of the cell components gets small relative to the volume of the electrolytes, the flow battery approaches its theoretical maximum of energy density. Higher capacity systems are thus more efficient in this respect, as the majority of the weight is the electrolyte which directly stores energy.
Flow batteries can be employed both as a rechargeable secondary battery and a fuel cell. The earlier loaded electrolyte will be the alternative for the discharged electrolyte and thus it has the synergic significance.