With the gradual increase in the proportion of BESS (Battery Energy Storage System), the utilization rate of lithium battery storage is rapidly increasing due to its advantages such as high energy density, flexible application, and fast response.
BESS’s lithium battery storage is usually assembled in a container cabin with limited space.
It will continue to generate heat during charging and discharging, and its heat is difficult to conduct to the outside environment in time.
At the same time, the best working temperature of lithium batteries is 25-40°C.
If it runs at a high temperature for a long time, it will have an irreversible impact on the working efficiency, performance, and life of the BESS. If it is serious, it will cause the risk of thermal runaway and cause safety accidents.
This blog provides an in-depth analysis of how to choose a heat dissipation method to achieve safe cooling of battery storage.
Tip: Click on the orange highlighted text to learn more.
How is the heat in the battery storage conducted?
Before understanding cooling, we first recognize heat transfer, and then find the law and solve it.
There are three ways of heat transfer, namely heat conduction, heat radiation, and heat convection.
Heat conduction refers to the transfer of heat from one part of a system to another. Or a phenomenon that is transmitted from one system to another.
Thermal convection refers to the process in which the temperature tends to be uniform through circulating flow between the hotter part and the colder part of the liquid or gas.
Thermal radiation refers to the energy emitted by an object due to its temperature.
The internal structure of the container-type lithium battery energy storage system is as follows:
The general size of a BESS container is a length of 12 m, a width of 2.4 m, height of 2.8 m.
A total of 12 sets of battery clusters are placed in the battery compartment, and 6 sets are placed on each side. Each cluster consists of 15 battery banks.
This also results in a close distance between them and faster heat transfer, making them more prone to thermal runaway and explosion problems.
Once it happens, the amount of loss will be very large, whether it is a home solar energy storage system, a wind-solar hybrid energy storage system, street lights, and so on.
As long as they are designed and installed with lithium batteries, PVMars will install BMS, air-cooled, or liquid-cooled heat dissipation devices on each lithium battery. To ensure your safety during use.
What are the ways to cool down the battery storage?
To solve the problem of cooling the energy storage battery, the current mainstream heat dissipation methods for battery packs are air cooling and liquid cooling.
Taking air cooling as an example, the temperature of the battery module increases during charging and discharging. The heat is first transferred to the air in the cabin by thermal radiation.
Then the air in the cabin and the air outside the cabin conduct heat transfer through heat convection to reduce the temperature in the cabin.
Air convection is generally divided into two types, namely natural wind and mechanical wind. Air flows into the container from the air inlet, and flows out from the air outlet after heat exchange.
The efficiency of natural wind is low, and it is rarely used except for specific conditions.
The mechanical wind needs to be used with the air conditioning system, which can efficiently adjust the air temperature.
For example, in the case of PVMars in Papua New Guinea, an air conditioner was designed for a 500kW solar energy storage system to cool down its 2V gel battery.
At present, for this heat transfer process, air-cooled heat dissipation focuses on the following three types of research:
1- Change the forced air cooling condition
2- Change the duct design
3- Add deflectors in the battery compartment
Among them, there are two ways of forced air cooling:
1- Increase the heat dissipation surface area of the heat source
2- Speed up the air velocity per unit time
The former can be achieved by installing heat sinks on the surface of the battery module, and the latter can be achieved by installing fans, air conditioners, etc.
However, changing the design of the air duct requires higher requirements, and the air duct includes the central air duct connected to the outlet of the air conditioner.
The windshield in the main air duct, the outlet of the air duct, and the windshields at both ends of the battery rack.
According to the characteristics of the container, it is symmetrically arranged.
The efficiency of the existing air duct design is high, and it is difficult to further improve it.
Finally, a deflector is added to the battery compartment.
Depending on the number and position of the deflectors, the distribution of the airflow field, temperature distribution, and cooling in the battery compartment will change.
Although their emphases are different, the purpose of the three methods is the same.
Increase the wind speed in the battery compartment to increase the disturbance range of the heat exchange air in the compartment.
Finally, the effect of improving the heat exchange efficiency in the battery storage compartment and keeping the temperature of the battery module within the normal operating temperature is achieved.
Generally speaking, air-cooled heat dissipation has the advantages of simple principle, convenient installation, and low cost, and is widely used in energy storage scenarios with low battery energy density and slow charge and discharge speed.
Next, about liquid cooling:
Liquid cooling is divided into internal circulation and external circulation. The internal circulation is set inside the battery compartment, and the external circulation is set outside the battery compartment.
Inner loop:
The battery PACK is in direct contact with the liquid cold plate, and the heat is transferred from the battery module to the inside of the heat transfer medium through heat conduction.
The heat-conducting medium flows from the inside of the cabin to the outside of the cabin.
And transfers heat from the inside of the battery compartment to the outside of the battery compartment through thermal convection.
Outside loop:
The temperature of the heat transfer medium can be adjusted to an appropriate range through temperature adjustment equipment such as air conditioners.
Liquid cooling uses cooling liquids such as water, ethanol, and silicone oil.
And dissipates heat through indirect contact between the evenly distributed flow guide grooves on the liquid cooling plate and the battery cells. Its advantages include:
1)Close to the source of heat, 95% efficient cooling
2) Compared with the container air-cooling solution of the same capacity, the liquid cooling system does not need to design air ducts.
The floor area is saved by more than 50%, which is more suitable for large-scale energy storage power stations of more than MW in the future.
3) Compared with the air-cooled system, due to the reduction of the use of mechanical components such as fans, the failure rate is lower.
4) Liquid cooling has low noise, saves power consumption of the overall system, and is environmentally friendly.
Air-cooled heat dissipation VS liquid-cooled heat dissipation:
There are many differences between liquid cooling and air cooling, such as different heat transfer media and different media circulation devices.
In terms of heat transfer medium, the air-cooled heat transfer medium is air. There are more types of liquid-cooled heat-dissipating and heat-conducting media, including water, ethanol, and refrigerants.
The specific heat of air is 1.4kJ/ (kg*K), and the specific heat of water in liquid medium is 4.2kJ/ (kg*K), three times that of air, so liquid cooling is more efficient than air cooling.
In terms of medium circulation devices:
Liquid cooling requires a main pipe to run through the battery storage system in the container, and each battery cluster is connected to a thinner branch pipe.
Each branch pipe is connected to the liquid cooling plate arranged on each battery PACK, and the heat exchange is performed by changing the type and flow rate of the heat transfer medium in the liquid cooling plate.
There are many forms of liquid cooling plates, including parallel mini-channel cold plates, and serpentine channel structure cold plates.
Streamlined flow channel cold plates, double-layer inverted flow channel cold plates, parallel divergent flow channel cold plates, and bionic wing flow channel cold plates, etc., the heat dissipation efficiency is also different in different forms.
Immersion liquid cooling means that the energy storage battery is directly immersed in a special insulating cooling liquid.
The heat generated during the charging and discharging process of the battery is absorbed by the cooling liquid and then enters the external circulation for cooling.
In general, the advantage of liquid cooling is high heat exchange efficiency, but the disadvantage is a high upfront cost.
It is suitable for the energy storage environment with high battery energy density, fast charging and discharging speed, and high power requirements.
Final thoughts and conclusions:
In the specific layout process of BESS, air-cooled heat dissipation and liquid-cooled heat dissipation are optional.
It needs to be considered according to the budget, the overall power size, the type of battery storage, the geographical environment of the installation, and the requirements for heat exchange efficiency.
Both of them can effectively cool down your battery safely.
From the perspective of the entire energy storage market, the two heat dissipation methods of air cooling and liquid cooling only have a difference in penetration rate.
And the question of whether the cost is right.
At present, among the lithium batteries produced by PVMars, in addition to the addition of air-cooled and liquid-cooled heat sinks.
Our internal engineers are still researching phase change materials, liquid cooling + air cooling mixed-use mode, immersion liquid cooling and heat dissipation, etc.
Adding more possibilities in the future will make customer uses PVMars’s batteries safer, more convenient, and more cost-effective.
