ESS mainly develops and produces all iron flow batteries, which utilize the oxidation-reduction reaction of iron elements to achieve the conversion between electrical energy and chemical energy, thereby completing charging and discharging. This type of battery has good safety, with a cycle life of over 20000 times and an energy storage time of 10 hours or more, but it is still in the early stages of commercialization.

Venture capital firms prefer such high-risk targets, and companies such as SoftBank, BASF, and investment funds under Bill Gates have provided financing for them. However, ESS has not been able to achieve profitability since its establishment. As of December 31, 2024, this company has incurred a cumulative loss of $780 million. By comparison, its revenue for the first quarter of 2025 was only $570000.

ESS admitted in its annual report that the company's energy storage product deployment is limited, and some aspects of the technology have not been fully tested on site. "With the expansion of commercial production and usage scale, we need to address major challenges in terms of production capacity, cost, performance, and manufacturing processes.

In fact, battery energy storage technology based on iron elements has not been widely commercialized. In April 2025, the National Development and Reform Commission issued the "List of Green and Low Carbon Advanced Technology Demonstration Projects (Second Batch)", which includes two iron-based liquid flow energy storage power plant demonstration projects, namely the 100 MW/400 MWh iron-based liquid flow energy storage power plant demonstration project (Phase I) of China Power Construction New Energy Group and the 200 MW/800 MWh iron-based liquid flow battery energy storage power plant demonstration project (Phase I) of China General Nuclear Power New Energy. The former also uses all iron liquid flow batteries, and the technology comes from the Hubei enterprise Ju'an Energy Storage. Public information shows that Giant Energy Storage has completed at least three rounds of financing worth tens of millions of yuan since its establishment in 2021.

In addition to all iron flow batteries, there are also various technological routes on the market, such as iron chromium flow batteries and zinc iron flow batteries. Several companies in China are continuously developing iron chromium flow batteries, such as the Central Research Institute of State Power Investment Corporation and China National Energy Storage Corporation. Among them, Zhonghai Energy Storage won the bid for the 50 MW/300 MW project in Huiyang, Guangdong in April 2025, and announced the completion of a Pre-A++round financing of over 100 million yuan in May.

Zinc iron flow batteries are even more niche. Chinese company Weijing Energy Storage has introduced this technology from the United States and completed over 1 billion yuan in financing domestically. Currently, Weijing Energy Storage has established production bases in Yancheng, Jiangsu, Zhuhai, Guangdong, Baotou, Inner Mongolia, and other places.

There are still some technological bottlenecks in iron-based flow batteries, such as dendrite growth and hydrogen evolution reactions. Due to the immature industrial chain, their initial installation cost is several times that of lithium battery technology. However, these types of companies generally claim that due to their long lifespan, iron-based flow batteries have a lower cost per kilowatt hour throughout their entire lifecycle compared to lithium batteries.

Despite being on the brink of bankruptcy, ESS has still been awarded the titles of "Top Green Technology Companies in the United States in 2025" by Time magazine and "Most Innovative Companies in the United States in 2025" by Fortune magazine. This may be a microcosm of the situation of such long-term energy storage startups: on one hand, there is the enthusiastic pursuit of various capital under the carbon neutrality and vision, and on the other hand, there is the challenge of the "valley of death" that the industrialization of technological achievements must pass through.

Editor Huang Yanhua

Review Jiang Li

Transferred from: Southern Energy Observation