Supercapacitor is a new type of energy storage device whose performance is between that of traditional capacitor and rechargeable battery. It has the characteristics of fast charge and discharge of capacitor and energy storage of battery. Supercapacitors can be divided into electric double-layer capacitor and Faraday quasi-capacitor according to the storage mechanism. The electric double-layer capacitor mainly generates storage energy through the adsorption of pure electrostatic charge on the electrode surface. Faraday quasi-capacitor are mainly generated by reversible redox reactions on and near the surface of the electrode material, so as to realize energy storage and conversion.
Figure 1. The schematic illustration of the structure of a typical supercapacitor.
- Renewable energy field: The supercapacitor can be used for wind power generation to provide power for the paddle changing system and adjust the pitch. At ordinary times, the electric energy generated by the fan is input to the charger, which charges the supercapacitor until the energy storage power reaches the rated voltage. When it is necessary to change the rotor for the wind turbine, the control system issues instructions, and the supercapacitor energy storage system discharges, driving the system to work. Moreover, the application of supercapacitor as auxiliary storage device in photovoltaic power generation system mainly aims to achieve the following two functions. First, as an energy storage device, it stores the energy provided by the photovoltaic cell during the day, and supplies power to the load at night or rainy days when the photovoltaic cell cannot generate power. Secondly, with the photovoltaic cell and controller, realize MPPT (Maximum Power Point Tracking) control.
- Industrial field: Supercapacitors can be used in industrial fields such as forklifts, cranes, elevators, port machinery and equipment, various backup power sources, grid power storage and others. For example, when the forklift or crane is started, the energy stored in the supercapacitor will provide the instantaneous power needed for lifting and lowering in time. At the same time, the electrical energy stored in the supercapacitor can assist in lifting and hoisting, thus reducing oil consumption and emissions, and meeting other necessary electrical functions. In addition, supercapacitor energy storage system, as a necessary energy buffer link of microgrid, can provide effective reserve capacity to improve power quality and improve system reliability and stability.
- Transportation field: Applications of supercapacitor in transportation include regenerative braking systems, start-stop technologies for cars, buses and rail vehicles, low-temperature start-up for trucks and heavy transport vehicles. For example, during the operation of subway vehicles, due to the short distance between stations, trains start and brake frequently. Therefore, the energy generated by regenerative braking can be stored using supercapacitor, which are typically 30% or more of the input traction energy. The operating temperature range of supercapacitor is -40°C-65°C, and the supercapacitors have good discharge ability in low temperature environment. When the car is in a low temperature environment, the discharge capacity of the battery decreases. The parallel connection between the supercapacitor and the battery can assist the car to start, which can ensure the normal start of the car.
- Teng W A, Hai C, Feng Y A, et al. Boosting the cycling stability of transition metal compounds-based supercapacitors[J]. Energy Storage Materials, 2019, 16:545-573.