At present, common energy storage technologies include capacity based supercapacitor energy storage, pumped storage, lithium-ion battery energy storage, compressed air energy storage, flow battery energy storage, and power based flywheel energy storage. The characteristics and adaptation scenarios of each energy storage technology are different. With the continuous refinement of system requirements, a single type of energy storage is no longer able to simultaneously meet the requirements of construction cycle, configuration flexibility, safety, response speed, energy storage duration, service life, economic benefits, and other aspects.

The hybrid energy storage system adopts 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. For example, in current common scenarios, lithium-ion batteries are mostly used for energy storage. In actual power plant frequency regulation work, the frequency of battery calls within 5 minutes accounts for over 80%, including a considerable proportion of high rate charging and discharging. Lithium ion batteries have to face long-term high rate shallow charging and discharging, which not only hinders the effective utilization of capacity, but also reduces the service life of the battery due to frequent high rate charging and discharging.

Introducing power type energy storage units into lithium-ion battery energy storage, supercapacitor energy storage can help reduce the frequency of high rate charging and discharging of lithium-ion batteries, improve battery life, and reduce the risk of thermal runaway.

Meanwhile, due to the large amount of high-power work shared by supercapacitors, the capacity and power configuration of lithium-ion batteries can be effectively reduced, which not only improves utilization efficiency but also reduces system investment costs. For power type energy storage (whether it is a flywheel or a supercapacitor), matching it with lithium-ion batteries can overcome their disadvantages of low energy efficiency and high unit cost.

Hybrid energy storage can also be configured in wind and solar power plants to improve the efficiency of renewable energy generation utilization. Renewable energy generation represented by wind power and photovoltaics has strong volatility and intermittency. The large-scale development and utilization of renewable energy will simultaneously face the impact of short-term fluctuations on electricity quality and long-term peak shaving issues, which requires energy storage systems to possess characteristics such as high rate, fast response, large capacity, and high safety.

By designing hybrid energy storage systems, the advantages of different energy storage technologies can be integrated to achieve a leap in performance. The power unit in the hybrid energy storage system can quickly respond to achieve short-term fluctuation smoothing, while the capacity unit can achieve long-term peak shaving, thereby improving the controllability and utilization efficiency of renewable energy generation.

Due to the enormous potential of hybrid energy storage systems, China has gradually begun to implement hybrid energy storage projects.

If mixed energy storage is applied on a large scale, it can effectively improve the utilization efficiency of renewable energy generation, transmission and distribution equipment. However, the large-scale application of hybrid energy storage systems still has a long way to go, and its challenges include insufficient maturity of some energy storage technologies, high prices, and the need for in-depth research on the configuration and calling methods of hybrid energy storage. Therefore, the large-scale application of hybrid energy storage systems can be achieved through the following aspects:

1. Further develop various energy storage units, and the more mature the single energy storage technology, the higher the overall performance of the hybrid energy storage system;

2. Further determine system requirements and optimize the configuration of hybrid energy storage systems;

3. Establish the working logic and call priority of different energy storage units in the hybrid energy storage system, achieving the effect of 1+1>2;

4. Clarify the market position of energy storage in the energy system, clarify the work objectives and profit mechanism of the energy storage system.

With the advancement of technology, various energy storage technologies have reached or are close to commercialization levels. The organic combination of energy storage technologies with different characteristics is expected to improve the overall performance and economic benefits of energy storage systems. I believe this approach will play an important role in the large-scale development of renewable energy and the construction of a safe, low-carbon, and efficient new energy structure.