Led by the State Grid Hunan Electric Power Research Institute in collaboration with Central South University and ZH Energy, a 5kW/20kWh sulfur-iron flow energy storage device has recently been officially connected to the grid at the Hunan Energy Storage Demonstration Project Base of State Grid. The commissioning of this project marks a key leap for sulfur-iron flow battery technology from laboratory to engineering application, paving a new path for the development of long-duration energy storage technologies.

The sulfur-iron flow battery integrates the high safety and long-life characteristics of traditional flow batteries while significantly optimizing the cost of electrolytes. It is more suitable for long-duration, large-scale energy storage, with its core technical advantages reflected in the following aspects:

Inherent Safety with No Combustion or Explosion Risk: The use of aqueous electrolytes eliminates flammability and the risk of high-temperature expansion and deformation.

Abundant Raw Materials and Controllable Costs: The electrolyte raw materials are large-scale sulfur and iron compounds, which are widely available. Compared to vanadium batteries, the electrolyte cost is reduced by 85%, making it the lowest among all flow battery technology routes.

Fully Liquid Electrolyte with No Phase Transition Ris*: There are no physical changes involving ion intercalation or de-intercalation, and no solid metal or gas phase transitions occur. The inorganic compound structure remains stable and does not degrade.

High-Temperature Molecular Stability with No Cooling Required: The molecular structure remains stable at high temperatures without precipitation or crystallization, and the reaction activity is enhanced. Therefore, no high-temperature cooling system is needed, saving on system costs and operational energy consumption.

Low Marginal Cost of Electrolyte and Significant Long-Duration System Advantages: The cost advantage is more pronounced in systems with longer discharge durations, making it suitable for day-long 6-12 hour energy storage applications.

Hunan is one of the earliest provinces in China to build new energy storage facilities and is at the forefront of research in this field nationwide. The project "Hunan Province's Large-Scale Diversified New Energy Storage Multi-Scenario Integration and Coordinated Control Technology Demonstration Project," declared by State Grid Hunan Electric Power, has been successfully selected as the first batch of original technology demonstration projects for the new power system by State Grid (the only selected project in the energy storage field at that time).

The "Research on the Integration and Coordination Technology of New Energy Storage and Power Grid" project by State Grid Hunan Electric Power Research Institute focuses on the grid interaction capabilities of flow battery technologies, coordinated interaction and grid connection testing technologies for new energy storage, and the economic aspects of new energy storage. Among these, the low-cost sulfur-iron flow battery serves as a key demonstration vehicle for flow battery technology. State Grid Hunan Electric Power Research Institute, Central South University, and ZH Energy will conduct in-depth cooperation to systematically verify the inherent safety, long cycle life (over 15,000 cycles), charge-discharge efficiency, grid integration capability, and long-duration energy storage economic viability of sulfur-iron flow batteries through a multi-technology comparative testing system. This will provide empirical data support for the large-scale application of sulfur-iron flow batteries on the power generation side and grid side.

The economic breakthrough of flow battery technology is crucial for industrialization. Leveraging the price advantages of bulk materials like iron and sulfur, the electrolyte cost of sulfur-iron flow batteries is reduced by 85% compared to the all-vanadium system. As the world's first company to achieve engineering application of sulfur-iron flow batteries, ZH Energy successfully launched the world's first 1MWh sulfur-iron flow battery system in April of this year and will mass-produce 250kW/2MWh standardized modules in 2026. After achieving large-scale installation, the initial installation cost of sulfur-iron flow energy storage systems is expected to be reduced to below 1 yuan/Wh, with a full-life cost of electricity as low as 0.1 yuan/kWh. This represents a significant economic advantage compared to lithium and vanadium batteries, making it a safe and cost-effective large-scale energy storage solution.

The successful operation of this demonstration project not only verifies the technical feasibility of sulfur-iron flow batteries but also advances the complete closed loop of "technology research and development - engineering verification - industrial application." With the realization of technological iteration and economies of scale, this technology is expected to become an important support for the efficient integration of "source-grid-load-storage" in the new power system, driving the energy storage industry towards a safer, more economical, and sustainable development direction.

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