# Application of the Supercapacitor for Energy Storage in China: Role and Strategy
## 3 Development of China's Supercapacitor Field
### Application Status
#### 3.2.1 Microgrid  
The microgrid is a complex system involving power, load, energy storage, and control systems. The microgrid works in parallel with the power grid normally. When grid failures occur or the power quality declines, the microgrid is disconnected from the power grid and run independently. In the process of disconnecting, power unbalances and voltage sag often  
Figure 5: (**a**) Application field of supercapacitor. (**b**) Market segment capacity of supercapacitor from 2018 to 2020 in China. (**c**) Proportion of consumption structure in China’s supercapacitor market in 2020.  
happen. The supercapacitor can provide transient sustainment for the microgrid, achieve smooth transition of the two models, and guarantee the microgrid power quality. A study on simulation analyses on the model switch from grid mode to island mode showed that supercapacitors can effectively improve the power quality as well as stability and reliability when a power grid fault occurs and switch into island mode [36].  
The output power of micro sources, such as wind and solar energy, is greatly influenced by the environment and is extremely unstable. Due to the benefit of high power density, the supercapacitor can store energy when the load is low. Once the circuit reaches load peak, supercapacitors release the power reserved quickly, which can lead to reducing the impact of transient energy supply problems on the microgrid. Researchers simulated and analyzed the voltage of micro gird with and without supercapacitors, and they found that the supply voltage stability is greatly improved after supercapacitors are operated in the system. China made full use of photovoltaic power generation, wind power, small hydropower, and hybrid energy storage in the Qinghai-Tibet region, which is sparsely populated, and some prefectures and counties are nearly 1000 km away from the power grid. The researchers have overcome a series of key technical challenges and built a renewable energy power supply system featuring, for example, good power supply quality, strong anti-disturbance capability, high degree of automation, and easy construction and commissioning, which effectively solve the power supply problem in the project application area. Furthermore, microgrid technology has changed mode from laboratory technology to island application [37]. Niusan island, more than 60 km from Lianyungang, has been transformed into a microgrid with 30 kW rooftop photovoltaic power generation, 30 kW diesel generator and lead-carbon battery energy storage to meet the demand of power load for communication equipment, seawater desalination system, air conditioners, refrigerator, and daily lighting. Another island named Nanlu island, adopted wind energy, solar energy, diesel power generation and the battery energy storage integrated wind energy storage distributed power generation system. It uses solar energy and wind energy to store energy through four lithium battery packs and two supercapacitors to ensure a stable power supply while achieving low carbon and low emissions. The supercapacitor as an energy storage device exchanges energy with DC bus of power units, greatly improving the transient sustainability of the microgrid. However, its deficiency lies in the lack of a market operation mechanism, the initial investment following the way of the project, and the lack of market law of the input cost consideration model. Moreover, the whole industry lacks top-level design, and the industrial standard system is not perfect. The distribution of microgrid is relatively dispersed, and the labor cost of operation and maintenance is high [38].