CATL Launches Industry’s First 9MWh Energy Storage System: A Breakthrough in Capacity and Safety Concerns

The World’s First 9MWh Energy Storage System! Is Energy Storage “Stacked” Safely?

On May 7, CATL launched the world’s first 9MWh energy storage system. Compared to the more common capacities of 5MWh, 6.9MWh, and 7MWh available in the market, the introduction of a 9MWh system marks a significant milestone for the industry. Is energy storage capacity once again being upgraded?

To drive down energy storage costs and enhance the capacity and energy density of energy storage systems, the focus has shifted to improving the capacity of individual battery cells. According to incomplete statistics from Polar Star Energy Network, the largest existing container-based energy storage systems currently available have a capacity of 13.36MWh. This year, some integrators, led by companies like Envision and Huaneng, have achieved massive capacity limits of 7MWh and 8MWh by using larger storage cells. However, in the application market, mainstream energy storage systems used in actual projects still do not exceed 6MWh.

In contrast, the newly released 9MWh system from CATL is not just a breakthrough in “large capacity” but also represents a revolutionary design innovation. This new product, labeled TENER Stack, utilizes a stacked design with two cabinets (A and B), based on CATL’s high energy density batteries and a five-year zero-degradation technology. Compared to traditional 20-foot container systems, this product increases space utilization by 45% and energy density by 50%. The stored energy is sufficient to fully charge 150 electric vehicles or power an average German household for six years.

Additionally, to enhance energy storage compatibility and system efficiency, TENER Stack will support centralized and string-type PCS architectures. From the onsite photos, it is apparent that this product remains a DC-side energy storage system, with each cabinet having a capacity of 4.5MWh. When deploying an 800MWh energy storage project, the number of energy storage systems required using TENER Stack will be nearly one-third less than that of traditional 6MWh systems, thereby reducing the number of supporting PCS units and the hidden costs associated with oversized systems. This design improves land utilization efficiency by 40% and is expected to save developers up to 20% in total construction costs.

In terms of transportation, to address logistical challenges associated with transporting containers weighing over 36 tons, CATL developed a “two-in-one” design, which can reduce waiting times and specialized transportation costs by up to 35%. Each half-height unit is strictly controlled to weigh under 36 tons, ensuring compliance with 99% of global transportation regulations.

CATL’s Chief Technology Officer and President of European Energy Storage Systems, Xu Jinmei, stated that this product will meet the market’s demand for high energy density in large battery storage systems, smaller footprint, simpler AC side configurations, and flexible deployment.

However, CATL is not the first to introduce a stacked design for energy storage systems. Notably, Fluence, a leading global energy storage system company, released the world’s first stacked design energy storage system, Smartstack™, on February 13, which revolutionized previous integration design concepts. This high energy density system features an integrated AC/DC energy storage system with a voltage level of 1500V and utilizes 314Ah battery cells, achieving a total energy storage capacity of 7.5MWh. Its energy density is approximately 30% higher than current AC/DC integrated energy storage systems on the market and can accommodate energy storage demands of 2 hours, 4 hours, or even longer durations of 6 and 8 hours.

This high-density design enables projects to generate more power within existing footprints, thus lowering investment costs and allowing previously constrained sites to develop energy storage projects. The system is divided into a battery compartment and an intelligent slide. This design allows for the flexible replacement of individual components during maintenance, maximizing the online availability of the energy storage system. The upper section houses the battery compartment, which is modular and independently designed, with each module measuring approximately 1762x2528x2550mm and weighing 15.5 tons. It can easily scale economically according to customer needs and supports batteries from multiple suppliers to ensure competitive pricing and optimal performance. The lower intelligent slide functions as the electrical control compartment, measuring 7315x2200x1524mm and weighing 11 tons. It integrates advanced cooling equipment, power control system hardware, and cabling, combined with a comprehensive smart control and monitoring system that connects to the battery compartment for quick installation and predictive maintenance without downtime.

According to Fluence, this design also minimizes the project’s footprint, thereby reducing initial investment costs and enabling energy storage project development in previously space-constrained sites. Furthermore, the battery compartments are designed with isolation gaps to prevent overheating incidents from spreading throughout the energy storage system. Fluence claims that this protection, combined with a multi-layer cybersecurity architecture that exceeds global standards, comprehensively safeguards energy storage assets and operational revenue.

Official materials indicate that the innovative design of Smartstack guarantees a capacity utilization rate of up to 99%, combined with Fluence’s long-term service agreements, maximizing energy storage returns. Fluence has announced that the delivery of this energy storage system is expected to begin before the last quarter of 2025.

However, it is noteworthy that the energy storage industry has previously been skeptical about the efficacy of this stacked design approach due to challenges related to heat dissipation and maintenance, particularly given the risk of thermal runaway in batteries. Concerns have been raised by fire safety experts about the difficulties firefighters might face when trying to extinguish fires in double-stacked energy storage projects, posing significant challenges to the overall safety of energy storage assets.

Furthermore, industry professionals are well aware that lithium batteries, due to their high energy density, increase both capacity and weight, raising structural safety concerns for lower-tier buildings or systems from the weight of upper-tier energy storage systems. Some industry insiders have expressed doubts about the feasibility of rooftop energy storage solutions, suggesting they do not align with conventional construction practices.

Nevertheless, during the release of the new product, CATL mentioned that the TENER Stack uses lithium iron phosphate batteries, which have relatively superior thermal stability. The upgraded gas sensor’s sensitivity has improved by 40%, while the response speed of the suppression system has increased by 35%, providing earlier fire warning capabilities. The new three-layer insulation design has enhanced the fire resistance of the energy storage system to two hours. Additionally, CATL stated that this system complies with the IEEE693 seismic standards, capable of withstanding a 9.0 magnitude earthquake and a Category 5 hurricane.

In Fluence’s energy storage system, a real-time monitoring platform has been fully integrated, reportedly enhancing system intelligence through localized artificial intelligence. Supported by embedded control software, it can provide comprehensive analysis and forecasting across energy storage product portfolios, protecting assets while maximizing operational efficiency, thus lowering total investment costs and extending system lifespan to achieve a higher internal rate of return (IRR) than traditional energy storage solutions.

The Chief Technology Officer of European Energy Systems, Zhao Zhongsong, emphasized that CATL is not just providing energy storage products but rather offering globally applicable energy solutions. The 9MWh capacity is not the limit of energy density or space.

Ultimately, if stacked design can ensure safety in fire, construction, and transportation, energy storage systems can achieve higher energy density per unit volume through stacking. Therefore, the breakthrough point for large capacity in energy storage systems may not hinge solely on cell capacity, but rather on “height,” which might be the ceiling limiting the capacity of energy storage systems.