How to build a solar power energy storage systems

Battery system

It is energy storage battery system and adopts modular integrated design from cell to battery array. The battery management system adopts 3-level BMS control system. And provides highly reliable battery balance mode, safety management mode, thermal management mode, and provides rich monitoring projects.（Currently, lithium batteries are mainly used. You can directly cooperate with lithium battery manufacturers to design battery PACK Solution）

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Energy storage converter

It adopts advanced power devices and advanced digital control technology to optimize the control performance and improve the reliability of the system. It is suitable for different battery charging and discharging needs, and has modular design in structure, which is convenient for installation and maintenance. It also has two-way inverter, battery charging and discharging function and perfect display and communication function.

Container box

Including box and internal auxiliary functions, overall internal rack load-bearing design, heat dissipation design, lighting function, heat insulation function, dust proof, waterproof, pest proof, meeting IP54 protection grade, with access control function, which can meet the ljyenergy.com/application">application of the whole battery system in power storage and various complex environments.

Automatic fire fighting system

The automatic fire extinguishing system with heptafluoropropane as the main material is installed with automatic alarm device. Once a fire is detected, the electrical connection between the container and the external equipment can be disconnected in time. At the same time, the fire extinguishing device is started and the alarm information is uploaded to the back monitoring system, which has linkage function.

Temperature control system

The container adopts air conditioning, refrigeration and heating mode, air duct design, accurate air supply to the battery, and keeping the temperature consistency of the whole system. At the same time, the battery has thermal management mode.

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Design of Main Electric Wiring for Energy Storage System

The diagram is shown as following:

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As above picture shown, ESS consists of 9 cell clusters as one pace then 1 set of 500KW. Pre-charge circuit is set into the battery packs to guarantee system security.

Design of secondary communication of ESS

The communication management unit in the system control cabinet of energy storage system includes optical fiber Ethernet switch, BAU, ECS and other equipment.

ECS communicates with the monitoring background of the main control room through the switch. And the communication protocol is IEC 61850 or Modbus TCP.

The energy storage ECS is used to coordinate and control the system inside and unify the protocol standards. It uses mature real-time operating system and is equipped with high-speed field bus to ensure the safe and stable operation of the energy storage system.

The environmental temperature and humidity monitoring, smoke sensor and water immersion sensor in the container are collected and connected to the security monitoring system by TCP / IP protocol through Ethernet port.

What’s more, the camera in the container is connected to the video monitoring host in the main control room through the network cable.

Design of secondary electricity of ESS

The Secondary Electricy of ESS is mainly controlling the electricity and the power supply. Both of them will take power from the independent AC low-voltage distribution cabinet.

Plain Layout Design of Energy Storage Container

There are many requirements for the design of energy storage container. It is necessary to ensure that the lithium iron phosphate battery works at the rated working temperature and extend the working life of the energy storage unit. At the same time, the sensor probe, fire alarm and fire control system, temperature control system (equipped with industrial precision air conditioning), visual frequency monitoring system, temperature and humidity monitoring and other equipment should be configured to ensure the safe operation of the energy storage system and realize the long-term goal Process monitoring.

Remarks:

1)This equipment layout of the energy storage system is a preliminary design plan. After the project is finally implemented, final construction drawings as specification of whole project.

2)The container needs to use some rock wool to create a sealed battery storage space, in order to improve battery heat radiation management.

Design of Battery Cell Clusters

The battery system is to assemble the battery pack with certain electric quantity through certain series and parallel.

Typical design as below:

Battery system structural design has the following characteristics：

• The battery system consists of several battery clusters. Each battery cluster contains a fixed number of battery cartridges, and the battery cartridges in each battery cluster are in series.

• The battery cabinet is designed with thermal management ventilation ducts and cooling fans, which can use the cold and hot air of the air conditioning to perform thermal management on the battery.

• The single batteries inside the battery box are connected in series, and the battery boxes are connected in series through the aviation plug on the front panel using the power cable.

• The front panel of the battery cartridge integrates a BMU, a battery management unit, through which the voltage and temperature of a single battery can be collected.

5)The battery management system (BPU) is integrated into the battery high-voltage box. It is equipped with a total positive contactor, total negative contactor, pre-charging circuit, and fan cooling circuit. All contactors should be able to accept control of the battery management system.

Battery Management System（BMS）

The battery management system collects key data, such as single voltage, temperature, battery terminal voltage, current, and SOC, and has the functions of overcharge, over-discharge, and short circuit protection.

In order to prevent excessive charging and discharging of the battery, also extend the service life of the battery, monitoring the state of the battery, also to realize the charge and discharging management of the battery, as well as to ensure the stable and reliable operation, the system shall be equipped with BMS. Besides, the protection hardware shall be equipped with relays, circuit breakers, and fuses, etc. Moreover, the technology of balanced management and thermal management ensures the consistency, service life, and safety of the battery pack, and ensures the safe and reliable operation of ESS.

Overall architecture of battery management system：

BMS Three-level architecture diagram（Subject to actual project configuration）

Protection and monitoring functions of the battery system are implemented by the BMS battery management system，The battery management system (BMS) project is divided into a three-level architecture of BMU (level 1), BPU (level 2), and BAU (level 3). The main functions of each level of BMS as follows：

1)BMU is mainly responsible for collecting real-time information, such as voltage and temperature of battery modules. At the same time, automatic charging and discharging balance management, on-line detection, fault diagnosis.

2)BPU is responsible for the management of a battery pack, data communication with the BMU cluster, collection of operating information of the whole battery pack, and alarm and protection of abnormalities in the battery pack. At the same time, the SOC calculation, insulation detection and relay of battery equalization strategy analysis are carried out showing device adhesion detection, PCS data communication with this cluster, control related relays, and man-machine interaction with this cluster touch screen (HMI).

3)BAU is mainly responsible for data communication with BPU, real-time monitoring, and scheduling of the battery status of each cluster. And pass the data to the PC through the network, at the same time accept PC instructions and send them to the execution unit.

BMS main functions

Battery management system（BMS）main functions are listed below：

1)Analog quantity measurement function.

Including real-time battery string voltage detection, battery string charging and discharging current detection, single battery terminal voltage detection, battery multi-point temperature detection, battery string leakage monitoring and other parameters, and real-time single calculation SOC value and SOH value of cell and total battery cluster.

2)Battery system operation alarm functions.

Battery system over-voltage alarm, battery system under-voltage alarm, battery system over-current alarm, battery system high-temperature alarm, battery system low-temperature alarm, battery system leakage alarm, battery management system communication abnormal alarm, When the battery management system internal abnormal alarm and another status, it can display and report the alarm information, notify the PCS and the background monitoring system, and change the system operation strategy in time.

3)Battery system protection function.

When the battery management system is running, if the battery voltage, current, temperature, and other analog quantities exceed the safety protection threshold, the battery management system can achieve local fault isolation and remove the problem battery cluster from operation then report protection information at the same time, and proceed locally.

4)Self-diagnosis function.

This BMS has a self-diagnosis function. When the communication between the battery management system and the outside world is interrupted or the internal communication with the battery management system is abnormal. It can be reported to the monitoring system. In addition, it also has failures for other abnormalities such as analog data acquisition abnormalities. Self-diagnosis, local display and reporting on-site monitoring system functions.

5)Operation parameter setting function.

The parameters can be modified in BMS or the monitoring system of the energy storage power station through local and remote ways, and has the authority authentication function through a password to show local parameter modification. The battery management system provides communication protocol and command format for parameter modification. Parameter setting items include: upper limit voltage of single battery charging, lower limit voltage of single battery charging, maximum temperature of battery operation, minimum temperature of battery operation, over-current threshold of battery string, short-time temperature rise threshold of battery string, and local operation status display function.

6)Local operating status display function.

The BMS can display various operating status of the battery system locally, including system operating status display, battery cell voltage/temperature query and display, battery pack voltage/temperature query and display, battery String current/SOC/SOH query and display, analog quantity information display, alarm information display, protection information display, other abnormal information display, event and historical data recording function.

7)Thermal management.

During the charging process of the lithium battery module, a large amount of heat energy will be generated, which will make the temperature of the whole battery module rise. Therefore, BMS has the function of thermal management to monitor the temperature of the battery. If the temperature is higher than the protection value, the temperature control equipment will be turned on for forced cooling. If the temperature reaches the dangerous value, the battery pack can automatically quit operation.

8)Event and historical data recording function.

The battery management system can store all events and historical data of the battery system locally, recording more than 10,000 events and at least 180 days of historical data. Modification of operation parameters, alarm of battery management unit, protection action, start/end time of charging and discharging are recorded, and event recording has powered down keeping function. Each alarm record contains the defined limits, alarm parameters, and specifies the alarm time, date, and peak value within the alarm period.

9)Operation permission management.

It shall have the function of operation permission password management. Any operation that changes the operation mode and operation parameters shall require permission confirmation.

10)Remote and local operation.

It is capable of remote and local disconnection of DC circuit breakers and contactors, and shall have remote/local switching switches.

11)Battery pack string access/exit operation function.

The battery management system can accept the command issued by the energy storage monitoring system to the energy storage unit, and use the power contactor to complete the function of each battery pack string access/exit operation.

12)Balance function.

BMS has a balance function, and the consistency of the battery pack can be well maintained through an efficient balance strategy.

Energy Storage Bidirectional Converter（PCS）

The energy storage converter can realize the AC / DC conversion between the battery and the power grid, and complete the bi-directional energy flow between the two, and realize the charge and discharge management of the battery system, the power tracking of the grid side load, the power control of the battery energy storage system and the control of the voltage on the grid side under normal and isolated operation mode through the control strategy. The technical level of the energy storage converter directly determines the technical level of the electrical performance of an energy storage system, which is the core component of the energy storage system.

The electrical structure diagram is as follows：

Take BD500KTR-T as an example, its main performance characteristics are as following：

1)Integrated solution, support load, battery, grid, & access at the same time.

2) Integrated  EMS function, power supply is safe & stable, and energy utilization is maximized.

3) Flexible support for lithium batteries & lead-acid batteries.

4)Perfect protection function on protect inverter & battery.

5)Multiple working modes can set flexibly .

6)Pre-judgment of battery capacity & discharge time.

7)CAN  & RS485 interface，Modbus communication protocol.

8) Seamless switching between on & off-grid, uninterrupted supply of load.

9)Off-grid cold start function, support multi – machine parallel function.

10)Low-power fan, with intelligent temperature control system.

System Control Cabinet

1 system control cabinet is selected and configured in this project, which contains ECS local monitoring system, battery array management system APU, UPS, display control board, video surveillance video recorder, switch, I/0 extension module, router, 24V switching power supply and other equipment, mainly playing the functions of DC bus (9 in 1 out) and communication management.

1)DC confluent unit.

9 Battery clusters of the energy storage system are connected to PCS through a DC switch to provide DC power to PCS. The DMU in the cabinet detects the total DC voltage, current, charging and discharging quantity after the confluence, uploads data or state information to BAU through CAN communication, and receives demands of dividing and closing of main DC confluences switch from the battery stack or the command in the monitoring background.

2)Communication management function.

The battery array management unit BAU is installed in the cabinet to collect the data information and status signals of the battery management unit (BMU) and the battery cluster management unit (BPU), and manage the battery modules of each battery cluster according to the data information. Display all battery information on the touch screen. It communicates with PCS through CAN or RS485. And through MODBUS TCP/IP transmits data to the monitoring background and accepts commands from the monitoring background.

The AC Distribution Box

The AC distribution box mainly includes the strong current part and the weak current part. The overall electrical layout of the box follows the principle of separate layout for strong and weak currents. The low-voltage AC power distribution system is three-phase five-wire, which provides independent control power and 220V single-phase AC for AC electrical equipment such as lighting, switches, switching power supplies, air conditioning, fire protection, temperature and humidity sensors, water sensors, sockets, etc.

According to site conditions and design, the project uses 1 AC distribution box. Since AC distribution boxes are relatively common, which can be easily customized according to actual applications.

Temperature Control System Design

The temperature control system is composed of industrial air conditioners, integrated air ducts (built-in flow regulators), cabinet air ducts, built-in cooling fans, temperature and humidity sensors, etc., and performs thermal performance analysis (CFD) according to the operating conditions of the battery system. The intelligent control of the thermal management system realizes the effective control of the temperature inside the container.

1)Basic principles of temperature control system design.

* The container integrates heating and cooling air-conditioning, which can realize heating and cooling functions;

* An overall air duct and fan are arranged above the container to achieve uniform temperature distribution throughout the room;

* The battery cabinet has built-in air ducts and equipped with fans to achieve uniform temperature distribution within each cabinet;

* Carry out the overall heat preservation of the cabinet, and use materials such as rock wool to reduce heat exchange with the outside;

2)Design features of temperature control system

* The temperature control system can strictly control the operation and standby temperature of the battery pack, and has a dehumidification function. It can start different thermal management control modes according to different working conditions, and the internal environmental temperature of the container is controlled at 15°C~35°C.

* The container integrated air conditioner has many advantages, such as wide working range, remote communication, active and passive control, etc. It has cooling and heating functions and fresh air functions.

* The excellent thermal management structure design can ensure the uniformity of the cell temperature and control the temperature difference of all batteries in the container within 8°C.

* The reasonable arrangement of temperature and humidity sensors in the container and battery cabinet effectively ensures the accuracy of environmental temperature and humidity control.

* The whole container body is designed with thermal insulation materials to effectively reduce heat exchange with the outside world, ensuring the thermal performance of the system and significantly reducing system energy consumption.

* Real-time monitoring of various parameters, using different thermal management strategies according to different operating conditions, to achieve the unity of temperature control performance, energy saving and environmental protection.

3)Battery box heat dissipation design

* The module is supported and fixed by the bottom beam structure, which can effectively increase the contact area between the surface of the module and the cooling air while reducing weight, and improve the thermal management performance;

* A guide structure is added at the tuyere to effectively control the cooling air volume and wind direction to ensure the uniform air volume of each cell inside the module.

4)Battery cabinet heat dissipation design

* A fan is installed on the top of the cabinet;

* A guide structure is added at the tuyere to effectively control the cooling air volume and direction to ensure uniform air volume inside the module;

* A hollow structure is added to the top of the air duct to achieve effective cooling in high temperature areas.

5)Container cooling design

* An overall air duct is set above the container to achieve uniform temperature distribution throughout the room;

* The guiding structure is added to the overall air duct to optimize the air inlet direction; the flange surface is added inside the overall air duct to ensure the uniform and reasonable air volume distribution of each route.

Design of Fire Extinguishing and Automatic Fire Alarm System

The fire-fighting system in the container adopts heptafluoropropane automatic fire extinguishing system, and adopts a full-submerged fire extinguishing method for the protected area. It is composed of temperature-sensitive smoke detectors, fire alarm controllers, heptafluoropropane fire-fighting devices, sound and light alarms, gas spray indicator lights and other equipment.

Once the fire is detected by the fire fighting system, the alarm information will be uploaded to BAU through RS485 interface. After receiving the alarm information, BAU sends out the linkage command to disconnect the electrical output interface of the battery system, close the equipment that has an impact on the fire extinguishing effect, and at the same time, start the fire extinguishing device and upload the alarm information to the background monitoring system.

It has linkage function. When the battery environment is rapidly heated or ignited due to overload, short circuit and other reasons, and the electrolyte leakage produces toxic and flammable gas, the gas detector and temperature sensing cable will also give early warning, and the controller will send an early warning signal to the monitoring system to remind the staff to check, deal with and eliminate the potential fire hazard.

After confirming the fire, it can be started by pressing the fire extinguishing start alarm switch Heptafluoropropane fire extinguisher can extinguish the battery box; when the warning information develops to the fire alarm, the host will also automatically extinguish the fire.

The fire alarm system has three control modes: automatic, manual and emergency start / stop. The battery room and electrical room are equipped with gas fire-extinguishing protection and smoke detector and temperature detector.

When any smoke detector or temperature detector in the gas fire protection area gives an alarm, the gas fire extinguishing controller will send out an alarm to remind the staff to pay attention to the site conditions of the protection area; at the same time, the fire alarm signal will be sent to the fire control center alarm host.

When the smoke detector and temperature detector in the gas fire protection area alarm at the same time, the gas fire extinguishing controller will send the alarm signal to the fire control center, The automatic gas fire extinguishing controller starts the delay stage (0-30 seconds adjustable), sound and light alarm alarm and linkage equipment action (closing ventilation and air conditioning, etc.), which is used for evacuation personnel safety evacuation. After the delay, the gas fire extinguishing system sprays heptafluoropropane fire extinguishing agent to extinguish the fire, and lights up the gas emission indicator. At the same time, the gas emission signal is sent to the fire control center alarm host.

When the alarm controller is in manual state, the alarm controller only sends out alarm signal, but does not output action signal. After confirming the fire alarm, the operator on duty can press the “forced start” button on the alarm control panel to start the system to spray heptafluoropropane fire extinguishing agent. In order to prevent false start. If the “emergency stop” button is pressed, the system will not start the fire extinguishing device, and turn off the sound and light alarm inside the container, the sound and light alarm outside the box, and the gas spraying indicator light.

The flow chart of fire fighting system is shown below.

Video Surveillance System Design

The energy storage prefabricated cabin and the PCS prefabricated cabin are respectively equipped with surveillance cameras, and the video monitoring is realized by the hard disk video recorder NVR to ensure comprehensive surveillance.

The video monitoring information is connected to the video monitoring host in the main control room through Ethernet communication. Among them, the video surveillance video recorder and network switch are installed in the system control cabinet, and the video data is stored on-site. The hard disk capacity is not less than 4TB, and it is recorded cyclically.

Video surveillance is equipped with UPS power supply, independently installed in the system control cabinet, floor-standing installation, with a capacity of 4kVA, which can meet the needs of important equipment such as video surveillance, fire control controllers, and high-voltage control boxes for 1 to 3 hours of standby power supply.

Flame-retardant Insulation System Design

As I mentioned earlier, containers need rock wool to create a sealed battery storage space for battery heat management. The walls between the battery room and the PCS room inside the container are filled with rock wool, which can effectively prevent heat from being transferred to each other between the partitions.

Besides, the specific rock wool materials used will be different according to the actual situation

Lighting System Design

Explosion-proof lamps are used in the container, and an evacuation indicating device (emergency time greater than 1.5 hours) is installed. The power source is connected by the newly added lighting distribution box.

All lamps and lanterns should be arranged at a sufficient distance from the surrounding live equipment and easy to maintain.

Emergency lighting is installed in the energy storage device room, powered by the lamp’s own battery, and the power supply capacity is sufficient to maintain emergency lighting for two hours. The lighting design should meet the illuminance requirements in the room. And the illuminance of the energy storage room reaches 300Lx.

Design of Temperature & Humidity Monitoring System

The temperature and humidity inside the container have an important influence on the normal operation of the equipment. Therefore, temperature and humidity sensors are installed at both ends of the container to monitor the temperature and humidity values in the container in real time.

Once the temperature and humidity are found to exceed the set value, the air conditioner will be activated to control the temperature and humidity, and the humidity in the battery compartment will drop to 40. % which is within the safe range.

When the temperature and humidity exceed the set maximum alarm value, and the time exceeds 10 minutes, the alarm will be activated, and the background monitoring will send over temperature and humidity alarm information.

* The default temperature of the battery compartment is 35 degrees Celsius, and the level 2 alarm value is 45 degrees Celsius.

* The default humidity level control value of the battery compartment is 80%, and the level 2 alarm value is 95%.

The temperature and humidity sensors are installed in important parts of the container to monitor the environmental temperature and humidity. The current temperature and humidity values can be seen in the temperature and humidity sensor interface in real time, and the data can also be uploaded to the remote monitoring platform through the battery management system for remote real-time monitoring of temperature and humidity.

Design of Electrical Interlocking System

The container is equipped with safety equipment such as smoke sensor, temperature and humidity alarm. The smoke sensor, temperature and humidity alarm and the control switch of the system must form an electrical chain. Once a fault is detected, the container will notify the user through sound and light alarm and remote communication, cut off the battery equipment that is running to prevent electrical accidents.

When the humidity sensor detects that the humidity in the container does not meet the requirements, the battery complete equipment shall take effective measures to make the indoor humidity meet the working requirements.

Mechanical interlocking System Design

The container will not be opened by a thief under outdoor conditions. When a thief tries to open the door forcibly, the access control will generate a threatening alarm signal.

At the same time, it will send an alarm to the monitoring background through Ethernet remote communication. The alarm function should be blocked by the user manually.

Design of Safety Escape System

Clear sign for fire exit in the container. Once any dangerous, the staff can follow the safty signs to escape then can turn off the running set of battery equipment manually, also conduct the warning system to inform all users.

The fire exit sign should be labeled in round shape with reflective bands.

As below shown:

Lightning protection grounding design

The container shall be provided with bolt mounting and fixing mode. Bolt fixed point and the whole container all non-functional electric conductor (normally not charged container metal shell, etc.) and reliable unicom, at the same time, the container in the form of copper platoon to offer two place to meet the requirements of the most stringent power standard, to provide customers with the pick up location must be with the whole container non-functional conducting equipotential connection form a reliable conductors. The pick-up point is located diagonally on the container.

The top of each container is equipped with a reliable and high-quality lightning protection system. The lightning protection system is connected to two grounding copper bars provided by users through earthing flat steel or earthing round steel. The effective cross-sectional area of the conductor in the grounding system is not less than 250mm. Grounding resistance less than 4 Ω.

Each container has grounding copper bars, BMS cabinets, monitoring cabinets and other ground wires connected to the internal grounding copper bars. The grounding copper bars inside the container are connected to the external copper bars through the 250mm conductor, and the external copper bars are connected to the grounding flat steel.

A high quality flame retardant insulating pad with insulation voltage no less than 3kV and insulation thickness no less than 5mm shall be laid in the non-in/out area at the bottom of the energy storage system.

Protection strategy design of energy storage system

*Energy Storage Control System  (FOUR-level system)

The Energy Storage Control System is divided into four levels, namely, the equipment layer, the interval layer, the station control layer and the cloud control layer. The local monitoring system ECS is located at the interval layer, responsible for the control and protection of the equipment layer and reporting data to the superior station control system.

ECS is the core equipment to realize system operation and protect BMS, respectively scheduling BMS and PCS. PCS is a charging and discharging device for energy storage system, which is controlled by BMS and ECS respectively. BMS is the real-time monitoring and protection of the battery system, which can control the standby and shutdown of PCS, and is controlled by ECS.

ECS is a key subsystem of the energy storage system to execute the protection strategy, monitoring BMS, PCS, AC circuit breakers, fire protection, temperature and humidity sensors, UPS, and electricity meters. ECS accepts THE fault information of BMS and PCS. For the specific fault information of BMS and PCS, please refer to the communication protocol and the point table.

ECS monitors the equipment fault information and equipment signal fault information, and controls the standby or shutdown of the system to ensure the safe and reliable normal operation of the energy storage systems.

Cable selection and cable fire plugging design

The selection and laying design of cables shall comply with the current national standard “Cable Design Code for Power Engineering” (GB 50217-2007). Dc and AC cables are armoured, and communication cables are shielded twisted pair. The ac cables for cable trenches and overhead laying are steel wire armored cables; Direct buried and pipe buried AC cables shall be steel tape armored cables.

The specific design and selection of DC side and AC side should be based on the actual situation.

Fire prevention of cables shall meet the “Design Code for Electric Power Engineering Cables” (GB 50217-2007). The cable (trench) is blocked through the wall, the bottom of the cabinet, the cable is blocked through the floor, the cable communication is blocked through the cabinet, the cable tunnel fire resistance wall, the cable shaft is blocked, the cable is blocked through the pipe mouth, the outdoor terminal box is blocked, the fire protection of important cables and circuits, the fire protection of the intermediate joints of important parts of the cable. During the construction of cable fire plugging, there is a special person to supervise and make records to prevent leakage.