As the share of renewable energy in the power grid continues to rise, the duration of energy storage plays a crucial role in ensuring the stable operation of modern power systems.
In recent years, the share of renewable energy sources, primarily wind and solar, in the grid has steadily increased. These sources are characterized by high intermittency and instability, placing significant strain on the grid's load.
Data shows that when wind and solar energy account for 50%-80% of the total power generation, energy storage duration must exceed 10 hours to support a stable power grid.
Currently, the average energy storage duration in China is approximately 2 hours, which is insufficient to support the new power systems with high proportions of wind and solar power generation.
According to data from GGII (Gaogong Industry Research), the average energy storage duration for new energy storage projects in China is 2.2 hours. Of these, 12.9% of the installed capacity is for projects with less than 2 hours of storage, 74.6% for projects with 2-4 hours of storage, and 12.5% for projects with more than 4 hours of storage.
Energy storage can currently be classified based on duration into short-duration storage (<1 hour), medium-to-long-duration storage (1-4 hours), and long-duration storage (≥4 hours). However, there is no universally accepted definition for long-duration storage globally.
In China, long-duration energy storage is generally classified as storage technologies with durations of 4 hours or more, while in the United States, long-duration storage refers to technologies that can discharge at rated power for no less than 10 hours.
While medium-to-long-duration storage remains the dominant technology, primarily using lithium-ion batteries, short-duration and long-duration storage systems also hold significant market potential. These systems have driven the development of technologies such as supercapacitors, flywheels, sodium-ion batteries, and liquid-cooled storage.
Looking ahead, the future energy storage market will be a combination of diverse durations, technologies, and applications, with various sub-markets and applications emerging for different storage durations.
In the energy storage industry, short-duration storage technologies are primarily used in high-frequency applications such as frequency regulation, ramping, and peak shaving within the power system, as well as for intra-day peak shaving and improving power quality on the user side. These applications require rapid response times and precise regulation capabilities from the energy storage systems.
Current main short-duration storage technologies include supercapacitors and flywheel energy storage.
Specifically, supercapacitors excel in providing instantaneous power and rapid emergency response capabilities, making them particularly effective in improving power quality on the user side and smoothing renewable energy output. Flywheel energy storage, with its high efficiency, long lifespan, and low operational costs, plays an important role in rapid power system regulation.
It is also worth noting that primary and secondary frequency regulation in the grid is considered a form of short-duration storage. Primary frequency regulation requires response times in the order of seconds, meaning the system must quickly adjust to restore frequency stability when deviations occur.
This rapid response characteristic makes both primary and secondary frequency regulation essential aspects of short-duration storage. Flywheel energy storage, being a physical storage method that stores energy through high-speed rotation and converts kinetic energy into electrical energy when needed, is a typical example of short-duration storage technology.
As of the end of 2023, lithium-ion battery storage accounted for 97.4% of operational energy storage in China, while other emerging storage technologies such as lead-carbon, compressed air, and flow batteries accounted for only 2.6%. Additionally, the average storage duration of new energy storage projects across the country is 2.2 hours.
Regarding mainstream storage cells, the penetration rate of the 314Ah energy storage cell has already exceeded 40%. In terms of technological maturity, lithium-ion batteries are still far ahead of other new energy storage technologies in terms of scale, efficiency, and industrial support, making them the likely dominant technology for the next 5-10 years.
Clearly, lithium-ion batteries occupy an absolute leading position in China's energy storage market, especially in the medium-to-long-duration storage category.
This year, Highpower Technology, which began mass production of 314Ah cells, reported to GGII that the 314Ah cell is dominant in the 2-4 hour energy storage market. Highpower stated that the energy density of the 314Ah cell is significantly higher than that of the 280Ah cells. A 20-foot container can be configured with a 5MWh capacity, and it works well with PCS, making it suitable for medium-to-long-duration and long-duration energy storage.
Moreover, traditional storage technologies such as pumped storage are limited by factors such as construction cycles, site selection, and environmental concerns. Lithium-ion batteries can fill the gaps of traditional storage, offering a promising long-term development space.
Long-duration energy storage technologies are typically classified into four categories: mechanical storage, thermal energy storage, electrochemical storage, and chemical storage.
While mechanical storage is relatively mature, other long-duration storage technologies are mostly still in the demonstration or early commercialization stages. Challenges to large-scale commercialization include cost, efficiency, and reliability.
Among these, electrochemical long-duration storage has garnered significant industry attention, including flow batteries, lithium-ion batteries, and sodium-ion batteries.
Flow batteries, in particular, are ideal for long-duration storage due to their long cycle life. Some flow battery technologies can achieve more than 20,000 cycles, with overall lifespans extending beyond 20 years. In the first half of 2024, the domestic flow battery storage market added around 88MW/360MWh of capacity.
In terms of tendering, data shows that in the first half of 2024, 21 flow battery storage projects were tendered, including various technologies such as all-vanadium flow, zinc-iron flow, aqueous organic flow, and all-iron flow, with a combined total of around 1.6GW/5.4GWh.
In addition to flow batteries, several lithium-ion battery manufacturers have launched large-capacity lithium-ion batteries targeting the long-duration sector.
For example, REPT Battero has released the 564Ah Wending cell, which offers over 12,000 cycles and a service life of 25-30 years. EVE Energy has developed the 628Ah Mr. Big cell suitable for long-duration storage, and Hithium Energy Storage has launched the MIC 1130Ah long-duration energy storage battery. ETC Battery has also introduced a 630Ah cell for long-duration storage.
The long-duration energy storage market is expected to experience significant growth starting in 2025. By 2030, global renewable energy penetration is projected to reach around 60%-70%, and cumulative long-duration storage installations will likely reach 150-400GW (corresponding to 5-10TWh of energy storage capacity), providing a vast market space for lithium-ion, flow, and other energy storage technologies.
