1. Energy storage field: Liquid cooling solution becomes the mainstream trend
Temperature affects the capacity, safety, life and other performance of electrochemical energy storage systems, so thermal management of energy storage systems is required. The energy storage system is a complex system composed of a large number of batteries, PCS, BMS, EMS, temperature control, fire protection and other subsystems, among which the battery is the core component of the system.
The impact of temperature on the energy storage system is reflected in two aspects:
(1) Temperature affects the performance of a single battery cell. Too high or too low temperature will affect the normal use of the battery cell;
(2) Temperature affects the performance of the battery system. The temperature difference between multiple batteries will affect the consistency of the system. The consistency problem will affect the safety, efficiency and life of the system.
The impact of temperature on battery cell performance is reflected in:
(1) Capacity: High temperature will increase the internal resistance of the battery and cause the loss of active lithium ions. If the battery is kept at high temperature for a long time, the capacity will deviate significantly from the nominal capacity. The higher the temperature, the faster the capacity of the lithium-ion battery decays. In a low temperature environment, the transmission performance of the electrolyte is greatly reduced, which will also lead to a decrease in the capacity of the lithium battery. The capacity retention rate of lithium iron phosphate batteries is 60% to 70% at 0°C, and it is reduced to 20% to 40% at −20°C.
(2) Life: Temperature changes cause changes in the internal resistance and voltage of the battery, affecting the battery life. Studies have found that for every 1°C increase in temperature, the battery life is reduced by about 60 days.
(3) Thermal stability: High temperature will cause decomposition reactions in the internal materials of the battery, affecting the safe and stable operation of the battery. In a high temperature environment, the SEI film may decompose, which will lead to occlusion of the lithium ion channel, short circuit of the positive and negative electrodes, and generation of a large amount of heat. At the same time, a large amount of gas will be generated, leading to thermal runaway phenomena such as battery bulging and rupture. In low temperature environments, lithium dendrites may appear at the negative electrode of the battery and even pierce the SEI film, affecting battery safety.
It is generally believed that the optimal operating temperature range for lithium batteries is 10-35℃.
Lithium battery operating temperature range
The impact of temperature on the battery system is reflected in the consistency of the battery cells. During battery operation, differences in the charge and discharge states of each battery cell, differences in internal resistance, current fluctuations and other factors will cause differences in the aging state of the single battery after multiple cycles, which in turn causes differences in performance between single batteries. Studies have shown that the temperature gradient between modules reduces the capacity and life of the entire battery pack, so it is necessary to maintain the temperature uniformity between each single battery in the battery pack. In order to maintain the consistency of the single battery in the battery, the temperature difference between battery cells is required to not exceed 5°C.
Temperature distribution of battery pack in air-cooled system at 1.5C discharge rate
There are four thermal management solutions for energy storage systems: air cooling, liquid cooling, heat pipe cooling and phase change cooling. Currently, only air cooling and liquid cooling have entered large-scale applications, while heat pipe cooling and phase change cooling are still in the laboratory stage.
(1) Air cooling: Air is used as the medium, with the characteristics of simple structure and easy maintenance. However, air has low specific heat capacity and low thermal conductivity, which is suitable for scenarios with low cooling efficiency requirements.
(2) Liquid cooling: Liquid is used as the cooling medium. Commonly used liquid cooling media include water, ethylene glycol aqueous solution, pure ethylene glycol, air conditioning refrigerant and silicone oil. The cooling medium has a high heat transfer coefficient, large specific heat capacity, fast cooling speed, good cooling effect and compact structure.
(3) Heat pipe cooling: An efficient heat exchange element that relies on the phase change of the working fluid in a closed shell and tube to achieve heat exchange. Heat pipes have the advantages of high thermal conductivity, isothermal, reversible heat flow direction, variable heat flux density and constant temperature.
(4) Phase change cooling: Heat is absorbed by using phase change of phase change materials. Selecting materials with large specific heat capacity and high heat transfer coefficient will achieve good cooling effect. However, phase change materials themselves do not have the ability to dissipate heat and need to be combined with other heat dissipation methods.
Energy Storage Thermal Management Solutions
Characteristics of typical energy storage thermal management technologies
| Item | Air cooling | Liquid cooling | Heat pipe cooling | Phase change cooling | |
| Passive | Active | Cold end air cooling | Cold end liquid cooling | Phase change material + thermal conductive material | |
| Cooling efficiency | Medium | Higher | Higher | High | High |
| Cooling speed | Medium | High | High | High | Higher |
| Temperature drop | Medium | Higher | Higher | High | High |
| Temperature difference | Higher | Low | Low | Low | Low |
| Complexity | Medium | Medium | Medium | Higher | Medium |
| Lifespan | Long | Long | Long | Long | Long |
| Cost | Low | Higher | Higher | High | Higher |
Liquid cooling solutions have gradually developed into the mainstream solution in incremental energy storage scenarios.
From the supply side, the liquid cooling solution has the advantages of high technical maturity, good cooling effect, and positive impact on system performance.
(1) Safety: The liquid cooling solution has high heat dissipation efficiency and high protection level. It can cope with more complex working environments, reduce the possibility of thermal runaway, and improve system operation safety. Data show that the heat dissipation capacity of liquid is 3,000 times that of the same volume of air, and the thermal conductivity is 25 times that of air. In addition, the liquid cooling system has a higher protection level and can cope with more severe operating environments.
(2) Economic efficiency: To achieve the same control effect, the liquid cooling solution has lower energy consumption, which can reduce operating investment and improve the economy of the entire life cycle. In order to achieve the same average battery temperature, air cooling requires 2-3 times more energy consumption than liquid cooling. At the same power consumption, the maximum temperature of the battery pack is 3-5 degrees Celsius higher for air cooling than for liquid cooling. The liquid cooling system can save energy by up to about 50% compared with the air cooling system.
(3) High integration: Due to the better cooling effect of the liquid cooling solution, the integration of the energy storage system in the container is higher. Taking the SmartPropel Energy liquid-cooled energy storage system as an example, the capacity of a traditional air-cooled 40-foot container is 3.44MWh, while the capacity of a liquid-cooled solution for the same 40-foot container can reach 6.88MWh. For energy storage power stations of the same capacity, the use of a liquid-cooled battery system saves more than 40% of floor space.
From the demand side, the development direction of energy storage systems with larger capacity and more scenarios has increasingly higher requirements for thermal management, and the performance of liquid cooling solutions is more compatible with this.
(1) The scale of energy storage power stations is getting larger and larger. As the proportion of new energy in the power system increases, the demand for peak-shaving resources such as energy storage is becoming increasingly prominent, and the dispatching performance of large-capacity energy storage power stations is better than that of small-capacity power stations. Therefore, large-scale energy storage power stations show a trend of large capacity. At present, the scale of independent energy storage projects is rapidly breaking through 100 MWh and moving towards GWh.
In 2023, four 200MW/400MWh single power stations will be put into operation. As of September 2023, there are already 30 energy storage projects with a scale of more than 500MWh that have been planned and launched, with a total scale of 12.2GW/33GWh. Large-capacity power stations usually use large-capacity battery cells. As the size and capacity of the battery cells increase, the heat dissipation performance of the battery cells themselves deteriorates, so the requirements for the thermal management capabilities of the system will become higher and higher.
(2)The application scenarios of energy storage power stations are more diverse. According to the requirements of different energy storage durations, the application scenarios of energy storage can be divided into four categories: capacity type (≥4 hours), energy type (about 1~2 hours), power type (≤30 minutes) and backup type (≥15 minutes). In capacity type and energy type scenarios, energy storage is used for functions such as peak shaving and valley filling, off-grid energy storage, and emergency backup, showing a large capacity trend. The heat generation of a single project increases, and the requirements for thermal management increase. In the power type scenario, the energy storage system is required to absorb or release energy instantly and provide rapid power support. Rapid charging and discharging requires higher temperature regulation of the battery, and the importance of thermal management is highlighted.
2. Energy storage liquid cooling: The penetration rate is expected to reach about 45% in 2025
Domestic mainstream manufacturers have launched liquid cooling solutions, proving the popularity of liquid cooling. Among the existing energy storage projects, air cooling solutions account for a higher proportion, mainly because air cooling is simple in design and low in cost. However, as the scale and energy density of energy storage systems increase, the advantages of liquid cooling technology become more prominent.
Currently, companies such as CATL, BYD, Envision Group, SUNGROW, HyperStrong, Zhengtai New Energy, and SmartPropel Energy have launched liquid cooling products.
| Liquid cooling products launched by various companies | ||
| Company | Product Model | Availability |
| CATL | EnerOne | 2020 |
| BYD | BYD Cube | 2020.8 |
| SVOLT Energy | JU-Integrated Liquid-cooled Energy Storage System | 2021.4 |
| HyperStrong | HyperStrong | 2021.4 |
| Clou Electronics | E30 | 2021.5 |
| Chint Group | TELOGY 1500V Liquid-cooled Energy Storage System | 2021.6 |
| Envision Group | Smart Liquid-cooled Energy Storage Products | 2021.1 |
| Kehua Technology | Kehua S3 Liquid-cooled Energy Storage System | 2022.5 |
| Sungrow | PowerTitanlPowerStack | 2022.5 |
| SmartPropel Energy | 372KWh+200KW Liquid Cooling Energy Storage System | 2023.9 |
| Clou Electronics | Aqua Series Liquid Cooling Products | 2023.4 |
| Zhongtian Technology | MUSE1.0 | 2022.6 |
| JD Energy | Distributed Modular Liquid Cooling Energy Storage Cabinet Integrated | 2022.9 |
| Narada Power Sour | CenterL Liquid Cooling Energy Storage System | 2022.9 |
The basic components of the energy storage liquid cooling system include: liquid cooling plate, liquid cooling unit (heater optional), liquid cooling pipeline (including temperature sensor, valve), high and low voltage wiring harness; coolant (ethylene glycol aqueous solution), etc. According to the contact method between the coolant and the battery, there are two schemes: one is direct contact, the battery cell or module is immersed in liquid (such as electrically insulating silicone oil), allowing the liquid to directly cool the battery; the other is to set a cooling channel or cold plate between the batteries, allowing the liquid to indirectly cool the battery.
The energy storage liquid cooling system is safe, efficient and flexible. Take SmartPropel Energy “372KWh+200KW Liquid Cooling Energy Storage System” as an example:
(1) Safety: The system adopts IP55 protection + anti-condensation + structural seismic + six-dimensional limit design. Each pack has built-in perfluorohexanone flexible pipe + fire feedback detection. The system level adopts the design concept of three-level explosion-proof + three-level fire protection to achieve triple insulation monitoring and protection.
(2) Efficiency: Cluster-level controllers are used in liquid cooling energy storage systems. Through the intelligent control of current by the cluster-level manager, active balancing, intelligent switching and millisecond-level alarm response of battery cluster units are achieved. Experiments have shown that under the balancing effect of the cluster-level controller, the charging and discharging capacity of the entire life cycle is increased by more than 6%. At the same time, under the switching function of the cluster-level controller, intelligent balancing control of the battery cluster is achieved, and the annual availability of the system is >99%. Combined with intelligent temperature control and balanced control technology, the patented design of liquid cooling pack “Tongcheng”, the system heat dissipation “double circulation”, and the multi-level distribution of liquid cooling pipes, the temperature difference inside the container system is consistent and does not exceed 5°C, and the temperature difference between any packs does not exceed 3°C. Under the intelligent temperature control and balanced control technology, the probability of thermal runaway is effectively suppressed, and the system life is increased by 13%.
(3)Flexibility: The power density of the liquid cooling energy storage system is increased by 100%, and the capacity of 40 feet can reach 372Kwh. Taking the layout of the energy storage system with 200KW/372KWh as an example, the use of liquid cooling battery system saves more than 40% of the floor space. The use of prefabricated modular design reduces the initial investment cost by more than 2%.
Comparing the air cooling and liquid cooling solutions, the cost of temperature control equipment for liquid cooling is 0.09 RMB/wh, and for air cooling it is 0.025 RMB/wh. The overall cost of liquid cooling is expected to be reduced.
(1) Air cooling: A traditional 40-foot energy storage container with a capacity of 3.5MWh generally uses four 12.5kw air conditioning systems. The price of a single air conditioning system is about 22,000 RMB, and the temperature control price of a container system is calculated to be 88,000 RMB, corresponding to a unit price of 0.025 RMB/wh, and a value of 25 million RMB per GWh.
(2) Liquid cooling: A 40-foot container with a capacity of 5-6MWh requires two 40kw liquid cooling systems. The price of a single system is about 270,000 RMB, and the temperature control price of a container is 540,000 RMB, corresponding to a unit price of 0.09 RMB/wh, and a value of 90 million RMB per GWh. However, considering the high integration density of the liquid cooling system, the same capacity occupies a smaller land area, the civil construction cost is reduced, the same capacity uses fewer auxiliary materials such as connectors, and the overall system cost is reduced.
According to GGII estimates, the value of the energy storage temperature control industry will be around RMB 2.4 billion in 2021 (including overseas exports), and is expected to reach nearly RMB 16.5 billion in 2025. Among them, the liquid cooling market will account for about 45% in 2025.
Suppliers of energy storage liquid cooling temperature control solutions mainly come from data center temperature control, industrial temperature control and automotive temperature control manufacturers. The key to competition lies in the design capability of non-standard products, because different energy storage integrators have different product design solutions. Liquid cooling temperature control needs to be jointly developed with battery pack layout, liquid cooling pipeline design, etc., and integrated with batteries, so highly customized design is required.
| Major supplier of energy storage liquid cooling temperature control | ||
| Original industry | Company | Main customers |
| Data center temperature control | Envicool | CATL, BYD, Narada Power Sour, Clou Electronics, SmartPropel Energy, Sungrow, HyperStrong and related mainstream system integrators and battery manufacturers abroad. |
| henling Envirn | State Grid, etc. | |
| Industrial temperature control | Sanhe Tongfei | The company began to deploy energy storage temperature control business in 2020, expanding customers such as Sungrow, Clou Electronics, Narada Power Sour, Trina Solar, etc. |
| Goaland Energy | The main customers are distributed battery container integration manufacturers and battery manufacturers, and it has currently cooperated with CATL and others. | |
| Automotive thermal management | Jialeng Songzhi | CATL, SmartPropel Energy, etc. |
| Jiangsu Kingfield | The subsidiary Air Conditioning International Energy Storage related products began to supply to CATL, etc. in 2020. | |
SmartPropel Energy Company
SmartPropel Energy continues to invest in the research and development of energy storage battery thermal management technology. It currently has technical reserves and solutions for single-cabinet energy storage liquid cooling products based on lithium batteries, large-scale energy storage power station liquid cooling systems, and prefabricated cabin energy storage liquid cooling products. The company has all the liquid cooling system development capabilities, from one-dimensional and three-dimensional simulation design to single-board development, and ultimately has the ability to provide one-stop liquid cooling system solutions.
