A hybrid energy storage system is a combination of two or more energy storage technologies with different performance characteristics to improve the overall performance of the energy storage system and meet the refined needs of different scenarios and users. Due to the enormous potential of hybrid energy storage systems, China has gradually begun to implement hybrid energy storage projects.

Compared with single energy storage technology, hybrid energy storage technology combines multiple different energy storage methods, comprehensively utilizes the advantages of multiple technologies, compensates for the shortcomings of single energy storage technology, and also overcomes the problem of low operating efficiency of energy storage systems. At the same time, hybrid energy storage technology is more flexible and intelligent. Through new technological means such as computers and the Internet of Things, various energy storage devices in the energy storage system can be coordinated and controlled, maximizing the energy storage efficiency of the entire system. At the same time, dynamic adjustment and optimization scheduling of the power supply network can be achieved, enhancing the operational stability and power quality of the microgrid. Therefore, hybrid energy storage technology has the following advantages:

1、Extending the lifespan of batteries：The lifespan of batteries in hybrid energy storage systems is 1.5-2 times longer than that in electrochemical energy storage systems.

2、Improving the reliability and safety of energy storage systems: The reduction of battery system usage and charging and discharging rates in hybrid energy storage systems can significantly enhance the safety of the system and increase its reliability.

3、Reducing energy storage system costs: Hybrid energy storage helps to reduce system costs. Two or more energy storage systems can share most of the same power electronics and grid connection hardware equipment, reducing initial installation and maintenance costs.

4、Improving the economic viability of energy storage systems during operation: In the long run, off grid energy storage systems are expected to reduce energy costs in remote areas, making them more economically feasible. The service life of hybrid energy storage systems is relatively long, and the operating period is generally considered to be 10 years. The initial investment of hybrid energy storage systems is slightly higher than that of pure electrochemical energy storage systems. However, considering the replacement cost of energy storage equipment during the operation period, the total cost of hybrid energy storage systems during the 10 year total operation period is lower than that of pure electrochemical energy storage systems.

Therefore, hybrid energy storage has good development prospects and performance advantages, but it still faces some technical difficulties and economic bottlenecks in the development process. Therefore, when applying, it is necessary to analyze specific problems and find the truly suitable solution.