In the early hours, in the underground salt cavern of Anning, Yunnan, the air is being compressed to a high-pressure state; the Chuxiong Yi Autonomous Prefecture, home to the largest all-vanadium flow battery energy storage station in the country, has just been connected to the grid; in the Atacama Desert of Chile, a network-type energy storage system from a Chinese company is providing stable power to the driest region in the world.

These projects, thousands of miles apart, point to the same trend: energy storage technology is transitioning from "short-term" to "long-term."

As the proportion of new energy installations continues to rise, 4-hour energy storage can no longer meet the peak shaving needs of the power grid. Long-duration energy storage, which can discharge continuously for several hours, days, or even weeks, has taken center stage in history and has become a key support for energy transition.

In 2024, the proportion of renewable energy generation in our country has exceeded 35%, but the proportion of new energy storage projects lasting more than 4 hours is less than 16%, with an average duration of only 2.3 hours.

This mismatch between supply and demand highlights the deep-seated contradictions in the absorption of new energy.

"When the proportion of new energy generation in the energy structure of a country or region exceeds 20%, long-term energy storage of more than 4 hours will become a necessity; when the installed capacity proportion reaches 50% to 80%, the storage duration needs to exceed 10 hours," industry experts pointed out.

In Yunnan, the installed capacity of new energy has jumped to become the second largest power source in the province, but the intermittency and volatility of wind and solar power pose severe challenges to the grid's regulation capacity.

Zhao Tianshou, the director of the Carbon Neutral Energy Research Institute at Southern University of Science and Technology, pointed out that "without long-term energy storage, renewable energy cannot truly become the main energy source."

The all-vanadium flow battery, with its intrinsic safety, non-flammable and non-explosive characteristics, supports 100% deep charge and discharge, has a cycle life of up to 20,000 times, and zero capacity degradation, making it an important technological route for long-term energy storage.

In October 2025, the largest all-vanadium flow battery energy storage station in the country—the Yongren project in Chuxiong Yi Autonomous Prefecture—successfully achieved the commissioning and operation of the 220kV booster station. The project has a construction capacity of 300MW/1200MWh, and it took just over 170 days from startup to the grid connection of the booster station.

In Henan, the first "2.5MW/8.359MWh lithium iron phosphate + 0.5MW/2MWh all-vanadium flow" hybrid energy storage project demonstration station has officially commenced commercial operation, innovatively achieving the complementary advantages of "lithium batteries responsible for short-term high-frequency charging and discharging, and vanadium flow batteries undertaking long-term deep charging and discharging."

On October 28, 2025, the first high-altitude underground salt cavern compressed air energy storage project in the southwest region—the Yunnan Energy Investment Group Kunming Anning 350MW salt cavern compressed air energy storage demonstration project officially commenced construction.

The project innovatively utilizes four retired salt caverns as energy storage carriers, designed to operate at a pressure of 7MPa-9MPa, with a construction scale of 350MW/1750MWh and an energy storage duration of 8 hours. The project is equipped with an air compression system, a turbine power generation system, a thermal storage and exchange system, and a 220kV booster station. It is expected to be completed and put into operation in the first half of 2027, and will undertake multiple functions such as peak shaving, frequency regulation, and black start.

Despite facing competition from emerging technologies, lithium-ion batteries continue to make breakthroughs in the field of long-term energy storage. By 2025, the research and mass production of large-capacity energy storage cells will accelerate, resulting in more single cells with capacities of 500Ah+, 600Ah+, and even 700Ah+.

Haicheng Energy plans to globally deliver its 6.25MWh 2h/4h all-scenario large-capacity energy storage system in the second quarter of 2025, with the 4h energy storage system built on a 1175Ah energy storage cell.

The Nandu Power 690Ah ultra-large capacity energy storage battery will be mass-produced and delivered by the end of 2025, and the 20-foot energy storage system equipped with this battery can reach a capacity of 6MWh.

In 2025, the bidding results of two major long-term energy storage projects in Europe—those in the UK and Italy—have attracted industry attention.

The Italian transmission system operator Terna announced the results of its first energy storage auction, with a capacity of 10GWh. All winning projects are lithium-ion batteries, with operating times of 2, 4, 6, and 8 hours.

Similarly, the UK's energy regulator Ofgem has advanced 77 long-duration energy storage projects to the next phase in its new long-duration storage capacity price floor scheme, with approximately 70% of the capacity being lithium-ion batteries (excluding pumped storage).

In Chile, Trina Storage has partnered with Atlas Renewable Energy to jointly develop a 233MW/1003MWh grid-forming energy storage project, utilizing advanced grid-forming control strategies to enable the energy storage system to possess voltage source characteristics, autonomously establishing voltage and frequency without external grid support.

In Spain, Naturgy has begun the construction of its first battery storage projects, which will be configured in a hybrid manner with the company's Tabernas I and II solar parks, as well as the Piletas I wind farm and the El Escobar solar power station.

These four projects are the first phase of a larger plan, which aims to build ten battery storage sites by 2026, with a total capacity of 160MW/342MWh and an investment of over 80 million euros.

Despite the diversity of technological routes, long-term energy storage must overcome the economic threshold to achieve large-scale development.

Currently, the unit cost of flow batteries is about 2000 yuan/kilowatt-hour, far exceeding that of lithium batteries at 500 yuan/kilowatt-hour. When adding the operation and maintenance costs in special scenarios such as islands, the project return rate is generally less than 6%.

To solve this problem, the industry is enhancing project economics through various means:

In terms of business model innovation, some companies have moved beyond the mindset of equipment sales. For example, the Shanghai Lingang pilot project has increased the utilization rate of energy storage from 30% to 65% by sharing a multi-user energy storage pool.

In the hybrid energy storage project, the EMS system with millisecond-level switching achieves peak shaving, valley filling, demand response, and anti-backflow with one click, expected to save over 2.6 million yuan in electricity costs for the park annually, with an investment payback period of less than 5 years.

Hu Ming, the Party Secretary and General Manager of the State Grid Electric Power Planning Design Institute Co., Ltd., believes that "the core of the future is not about how much to build, but whether a sustainable business model can be established, gradually forming a revenue system of electric energy + electric capacity through capacity compensation and the synergy of electricity market mechanisms."

With the joint issuance of the "Special Action Plan for the Large-scale Construction of New-type Energy Storage (2025-2027)" by the National Development and Reform Commission and the National Energy Administration, it is proposed that within three years, the newly installed capacity of new-type energy storage nationwide will exceed 100 million kilowatts, and by 2027, the installed capacity of new-type energy storage will exceed 180 million kilowatts.

Long-term energy storage, as the "ballast" of the new power system, is becoming increasingly important.

The "Roadmap for the Development of New Energy Storage Technologies (2025-2035)" shows that the installed capacity of new energy storage in the country is expected to exceed 180 million kilowatts by 2027, exceed 240 million kilowatts by 2030, and exceed 300 million kilowatts by 2035.

With the rapid growth of wind power installations, new energy storage will become the core engine for building a new power system.

Hui Dong, the chief technical expert of the China Electric Power Research Institute, pointed out that in the next 10 years, solving the problem of new energy consumption will still rely primarily on daily regulation (8-hour energy storage). From the perspective of practice and technology, lithium batteries are the most economically optimal among various energy storage technologies, and by 2035, daily regulation-type long-duration energy storage will still be dominated by lithium batteries.

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