As the cornerstone of energy storage systems, energy storage batteries carry the important mission of providing stable and reliable energy to the system. An in-depth understanding of the core technical parameters of energy storage batteries will help us accurately grasp their performance characteristics and further improve the overall efficiency of the energy storage system. Below we will explain in detail the main technical parameters of energy storage batteries to help you better apply and manage energy storage systems.
1.Battery capacity (Ah)
Battery capacity is one of the important performance indicators to measure battery performance. It indicates the amount of electricity released by the battery under certain conditions (discharge rate, temperature, termination voltage, etc.), usually in Ah. Taking a 48V, 100Ah battery cell as an example, the battery capacity is 48V×100Ah=4800Wh, which is 4.8 kilowatt-hours of electricity.
Battery capacity is divided into actual capacity, theoretical capacity and rated capacity according to different conditions. The theoretical capacity refers to the battery capacity under the most ideal condition; the rated capacity is the capacity marked on the device that can continue to work for a long time under rated working conditions; while the actual capacity will be affected by factors such as temperature, humidity, charge and discharge rates, etc. Generally, Generally speaking, the actual capacity is smaller than the rated capacity.
2. Rated voltage (V)
The rated voltage of an energy storage battery refers to its design or nominal operating voltage, usually expressed in volts (V). The energy storage battery module is composed of single cells connected in parallel and in series. Parallel connection increases the capacity, but the voltage remains unchanged. After series connection, the voltage doubles, but the capacity remains unchanged. You will see parameters similar to 1P24S in the battery PACK parameters: S represents series cells, P represents parallel cells, 1P24S means: 24 series and 1 parallel - that is, cells with a voltage of 3.2V, the voltage is doubled after 24 cells are connected in series. , the rated voltage is 3.2*24=76.8V.
3. Charge and discharge rate (C)
Battery charge and discharge rate is a measure of charging speed. This indicator will affect the continuous current and peak current of the battery when it is working, and its unit is generally C. Charge-discharge rate = charge-discharge current/rated capacity. For example: when a battery with a rated capacity of 200Ah is discharged at 100A, and all capacity is discharged in 2 hours, the discharge rate is 0.5C. Simply put, the greater the discharge current, the shorter the discharge time.
Usually when talking about the scale of an energy storage project, it will be described in terms of the system's maximum power/system capacity, such as a 2.5MW/5MWh industrial and commercial energy storage project. 2.5MW is the maximum operating power of the project system, and 5MWh is the system capacity. If the power of 2.5MW is used to discharge, it can be discharged in 2 hours, then the discharge rate of the project is 0.5C.
4. Depth of charge and discharge (DOD)
DOD (Depth of Discharge) is used to measure the percentage between battery discharge and battery rated capacity. Starting from the upper limit voltage of the battery and ending with the lower limit voltage, all discharged electricity is defined as 100%DOD. Generally, the deeper the discharge depth, the shorter the battery cycle life. Battery power below 10% may be over-discharged, causing some irreversible chemical reactions that seriously affect battery life. Therefore, in actual project operation, it is important to balance the needs of battery operation time and cycle life in order to optimize the economy and reliability of the energy storage system.
5. State of Charge (SOC)
The battery state of charge (SOC) is the percentage of the battery's remaining power to the battery's rated capacity. Used to reflect the remaining capacity of the battery and the ability of the battery to continue working. When the battery is fully discharged, the SOC is 0. When the battery is fully charged, the SOC is 1, which is generally represented by 0 to 100%.
6. Battery state of health (SOH)
Battery health status SOH (State of Health) is simply the ratio of performance parameters to nominal parameters after the battery has been used for a period of time. According to IEEE (Institute of Electrical and Electronics Engineers) standards, after the battery has been used for a period of time, the battery capacity when fully charged is less than 80% of the rated capacity, and the battery should be replaced. By monitoring the SOH value, the time when the battery reaches the end of its life can be predicted and corresponding maintenance and management can be carried out.