Image: Convergent Energy + Power

Under the national "dual carbon" strategy, new energy sources represented by photovoltaics and wind power are developing vigorously. With the large-scale connection of photovoltaic and wind power, the demand for frequency regulation and peak regulation resources of the power grid has risen sharply. It plays an increasingly important role in increasing the power grid stability, improving the utilization efficiency of the power distribution system, etc. Electrochemical energy storage lithium-ion system, due to its low deployment environment requirements and many applicable scenarios, its application scale is growing rapidly. At the same time as the large-scale application, the safety of energy storage power stations has also attracted widespread attention.

New energy power-side energy storage, grid-side energy storage, and large-scale off-grid and micro-grid energy storage power stations often use containerized energy storage. Tens of thousands of cells are installed in containers through series/parallel connections. There is only a thin layer of diaphragm insulation between the negative electrodes. Electrical isolation mainly depends on insulating materials and electrical switches. The insulating materials may be carbonized at high temperatures and become conductive materials. The isolation switches may also break down under high voltage. Under the reverse high voltage and surge impact, the tube may also conduct abnormally. 

In the long-term and thousands of charge-discharge cycles, especially in the state of overcharge, over-discharge and over-temperature, it may cause short-circuit failure of the battery cells, partial loss of control, and safety problems in any of the battery cells. If there are no strict safety protection measures in advance responding to it may cause a chain reaction in the system, resulting in an explosion accident.

It is possible to solve the safety problem of the energy storage power station by increasing the insulating material and strength and constructing the copper and iron walls of the energy storage power station, but it will increase the cost of the power station and is not conducive to the large-scale promotion and application of energy storage. The safety of containerized energy storage can guarantee the safety of energy storage plants. The safety of containerized energy storage needs to start from the system plan, material selection, security design, etc, in order to comprehensively take into account the two important indicators of safety and cost. 

At present, the main safety technologies and measures adopted by containerized energy storage include new modular energy storage technology, aerogel thermal insulation materials, traditional electrical protection, thermal management and efficient fire safety systems.

1. Modular energy storage technology

The first-generation lithium battery simply connects the battery packs into clusters, and the second-generation lithium battery adds some intelligent battery management units on the basis of the first-generation lithium battery. However, a series of problems such as the high voltage of the DC bus in the lithium battery system and the risk of battery insulation, the uneven discharge between clusters, and the inability to mix the echelon batteries cannot be completely solved, which puts a question mark on the safe and stable application of lithium batteries. 

2. Aerogel

Aerogel is a solid material with a nanoporous network structure and filled with a gaseous dispersion medium in the pores, which is the lightest solid in the world. Aerogel is recognized as the lightest known solid material in the world and is a new generation of high-efficiency and energy-saving thermal insulation materials. Aerogel has the characteristics of high flame retardant performance, light volume, and low consumption, and has become the best choice for power battery cell insulation materials. It has been adopted by battery companies and new energy vehicle manufacturers. 

3. Electrical protection of energy storage power station

DC energy storage unit protection configuration: over-voltage protection, thermal protection and over-current protection, voltage and the current rate of change protection, charging protection; DC connection unit protection configuration: configuration of fuses, low-voltage DC circuit breakers, low-voltage DC isolation switches, and mid-span Battery protection, for multiple energy storage units, the DC connection units should be connected as far as possible to avoid loss of more power supply capacity in the event of failure; bidirectional converter (PCS) protection configuration: input and output side overvoltage protection, over frequency and under-voltage protection Frequency protection, phase sequence detection and protection, anti-islanding protection, overheating protection, overload, and short circuit protection.

4. Thermal management of lithium battery

In order to meet the environmental conditions of the project site and the normal use of the battery pack and supporting equipment under the operating conditions of the system, the container conducts thermal management control through the following aspects, mainly including air conditioning, thermal management design, thermal insulation layer, etc., thermal management system The temperature in the container can ensure the normal operation of the battery pack and supporting electrical equipment.

The temperature control scheme in the container is as follows: the temperature of each set point in the container is monitored in real time through the temperature probe. When the temperature of the set point is higher than the set start temperature of the air conditioner, the air conditioner operates the refrigeration function, and the special air duct is used to control the temperature of each set point in the container. The interior of the container is cooled, and when the temperature reaches the lower limit of the set value, the air conditioner stops working. When the temperature of the set point is lower than the set start temperature of the air conditioner, the air conditioner operates the heating function and heats the interior of the container through a special air duct. When the temperature reaches 15℃, the air conditioner stops working.

During the operation of the lithium battery, due to the existence of the internal electrochemical reaction and the influence of the increase of the ambient temperature, the inner cavity temperature of the battery will increase and the reaction will be intensified; while in the alpine area, due to the influence of the low temperature of the environment, the reaction in the battery will also be reduced. speed. The former can lead to a thermal runaway that can cause premature battery failure and safety issues, and the latter can also reduce the battery's charge-discharge capacity and efficiency.

5. Container fire safety

Compared with lead-acid batteries, lithium batteries of the same volume have higher density and more energy storage. After deflagration and fire, the flame will be jet-like, and the temperature of the fire source will be higher. At the same time, a large amount of toxic and harmful gases will be released, so the safety hazard is higher. big. When fighting a lithium battery fire, firstly, put out the open flame in time to avoid the rapid spread of the fire; secondly, reduce the thermal runaway reaction rate, so that the heat generated by the internal thermal runaway reaction of the lithium battery is released in an orderly manner; The fire reignited and spread rapidly.

Fire-fighting devices are integrated into the container, and most of them adopt a structure of no less than three levels, including early warning, alarm and action, and fire-fighting system devices, including detection controllers, fire control boxes, sound and light alarm bells/lights, temperature and salt fog sensors, perfluorohexanone gas fire extinguishing device. The installation principle of the detection controller should be close to the battery pack. Combined with the structure of the actual rack, the top space on the battery cabinet can be selected for installation. The fire extinguisher device adopts cabinet type heptafluoropropane fire extinguisher and aerosol fire extinguishing device. Among them, the cabinet type perfluorohexanone is installed in the battery room, and the aerosol automatic fire extinguishing series devices are installed in the electrical room.

The container is equipped with perfluorohexanone fire-fighting device. Once the smoke sensor and temperature sensor detect the high-temperature fire fault signal, the container can notify the user through sound and light alarm and remote communication, and at the same time, cut off the running lithium battery complete set of equipment. After 30 seconds, the fire fighting device released perfluorohexanone gas to extinguish the fire. Significant instructions are required on the escape door in the container: Please leave the container within the 30S after the fire alarm signal sounds.

Aerosol automatic fire extinguishing device is a new type of hot aerosol fire extinguishing device, which is a breakthrough product in the field of fire protection with ultra-high fire extinguishing efficiency and reliability. When a fire occurs, the fire-extinguishing agent is activated by electric activation or temperature-sensing activation, and a large amount of sub-nano-scale solid-phase particles and inert gas mixtures are rapidly produced, which are completely submerged in the form of high-concentration smoke. The formula acts on every corner of the fire. Through the multiple functions of chemical inhibition, physical cooling, and diluting oxygen, the fire is quickly and efficiently extinguished, and it is non-toxic to the environment and personnel.

Aerosols can also achieve three-level fire protection, using battery clusters as protection units, using centralized gas detection and sampling analysis, through the preset detectors in each PACK box, real-time detection of changes in the chemical composition of lithium batteries, by The chip analyzes and calculates the changes of various parameters, and conducts effective early fire suppression and prevention for the cells in the battery box to prevent the thermal runaway expansion of the lithium battery and the explosion of the energy storage cabinet. 

First, battery module fire protection: according to the size of the battery module and the capacity of the battery cell, installing the aerosol on the battery module can effectively extinguish the first fire of the battery cell (the first level of protection). Effective fire extinguishing methods can minimize thermal runaway loss; second, battery cabinet fire protection: install aerosol in the battery cabinet, with a protective space of 3m, which can effectively extinguish the second re-ignition or electrical fire in the battery cabinet (second level). The third is the fire protection of the storage container: the aerosol group can be installed in the container as the overall protection, the fire suppression of the whole container (third pole protection). With the first and second levels of protection, the third pole protection activation chance is greatly reduced, improving the overall fire safety.

The above describes the safety design of containerized lithium battery energy storage in detail. If you want to purchase a containerized lithium battery energy storage system, please contact us.