What do DOD, SOC, and SOH mean? Interpretation of Core Technical Parameters of Energy Storage Batteries.

What do DOD, SOC, and SOH mean? Interpretation of Core Technical Parameters of Energy Storage Batteries.

As the cornerstone of energy storage systems, energy storage batteries carry the important mission of providing stable and reliable energy for the system. Having a deep understanding of the core technical parameters of energy storage batteries can help us accurately grasp their performance characteristics and further improve the overall efficiency of the energy storage system. Below, we will provide a detailed explanation of the main technical parameters of energy storage batteries to help everyone better apply and manage energy storage systems.

1. Battery capacity (Ah)
Battery capacity is one of the important performance indicators for measuring battery performance. It represents the amount of electricity discharged by the battery under certain conditions (discharge rate, temperature, termination voltage, etc.), usually measured in Ah. Taking a 48V, 100Ah battery cell as an example, the capacity of the battery is 48V × 100Ah=4800Wh, which is 4.8 kWh.

The battery capacity is divided into actual capacity, theoretical capacity, and rated capacity according to different conditions. Theoretical capacity refers to the ideal state of battery capacity; Rated capacity refers to the capacity indicated on the equipment that can operate continuously for a long time under rated working conditions; However, the actual capacity will be affected by factors such as temperature, humidity, and charge discharge rate. 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 designed or nominal operating voltage, usually expressed in volts (V). The energy storage battery module is composed of individual cells connected in series. Parallel connection increases capacity without changing voltage, while series connection doubles voltage without changing capacity. You will see parameters similar to 1P24S in the battery PACK parameters: S represents series connected cells, P represents parallel connected cells, 1P24S represents 24 series and 1 parallel - that is, cells with a voltage of 3.2V. After 24 series connections, the voltage doubles, and the rated voltage is 3.2 * 24=76.8V.

3. Charge discharge rate (C)
The battery charging and discharging rate is a measure of the speed of charging. This indicator will affect the continuous current and peak current of the battery during operation, 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 with 100A, all capacity is discharged in 2 hours, and its discharge rate is 0.5C. Simply put, the larger the discharge current, the shorter the discharge time.

When it comes to the scale of an energy storage project, it is usually described in terms of system maximum power/system capacity, such as a 2.5MW/5MWh commercial energy storage project. 2.5MW is the maximum operating power of the project system, and 5MWh is the system capacity. If the discharge is carried out at 2.5MW and can be completed in 2 hours, the discharge rate of the project is 0.5C.

4. Depth of Charge and Discharge (DOD)
Depth of Discharge (DOD) is used to measure the percentage between a battery's discharge capacity and its rated capacity. Starting from the upper limit voltage of the battery and ending at the lower limit voltage, all discharged electricity is defined as 100% DOD. The deeper the discharge depth, the shorter the battery cycle life. A battery level below 10% may result in over discharge, leading to irreversible chemical reactions that seriously affect the battery's lifespan. Therefore, in actual project operation, it is important to balance the needs of battery operation time and cycle life to achieve the optimal economy and reliability of the energy storage system.

5. State of Charge (SOC)
The State of Charge (SOC) of a battery is the percentage of remaining charge to the rated capacity of the battery. Used to reflect the remaining capacity of the battery and indicate its ability to continue working. When fully discharged, the SOC is 0, and when fully charged, the SOC is 1, usually represented by 0-100%.

6. Battery Health Status (SOH)
State of Health (SOH) of a battery is simply the ratio of its performance parameters to its nominal parameters after a period of use. According to IEEE (Institute of Electrical and Electronics Engineers) standards, if a battery's capacity when fully charged is less than 80% of its rated capacity after a period of use, the battery should be replaced. By monitoring the SOH value, it is possible to predict the time when the battery reaches the end of its lifespan and carry out corresponding maintenance and management.

Conclusion
In order to better promote communication, Topband Energy Storage has established the "Energy Storage Learning and Exchange Group", aiming to provide a platform for industry professionals to exchange ideas, share energy storage trends, and find high-quality resources, and jointly explore the development path of the energy storage industry.