The battery energy storage system is an energy storage system composed of batteries and parallel voltage-type converters, which has the ability to quickly adjust and exchange (output or input) power (with or without) with the AC system.

The lithium battery energy storage can effectively achieve demand-side management, smooth load, shave peaks and fill valleys, and effectively balance the use of electric energy, thereby improving the efficiency of electric energy use. It is an important technology to alleviate today’s energy crisis and environmental pollution. Among them, lithium battery energy storage, especially lithium iron phosphate battery energy storage, has attracted more and more attention due to its unique characteristics. The importance to the future of mankind, in December 2011, the International Electrotechnical Commission (IEC) – < Electrical Energy Storage White Paper >, proposed three major application functions of energy storage in the power grid: improving user power quality, providing emergency power in case of power failure, Profit from the valley-to-peak electricity price difference.

Battery Storage

Lead-acid battery is the earliest lithium battery energy storage technology used by human beings. Lead-acid battery has a long development time, so the technology is relatively mature. The principle of lead-acid battery (VRLA) is simple, the electrode is mainly composed of lead and its oxide, and the electrolyte is Sulfuric acid solution, realizes redischarge energy through chemical reaction. Lead-acid batteries have the following advantages, such as low price of lead-acid batteries, high recycling rate, small self-discharge and good high current performance. However, the lead used in lead-acid batteries is a heavy metal, which has an impact on the environment and human body. In addition, lead-acid batteries have short service life, frequent maintenance, and lead-acid batteries have low energy and power density, which cannot meet the power and capacity. Large-scale energy storage scenarios that must be taken into account at the same time. This makes the development of lithium battery energy storage in the direction of energy storage technology unable to reach a new height.

Lithium battery energy storage

Lead-acid battery energy storage has many problems such as high investment, short life, pollution to the environment, and harm to the human body, while lithium iron phosphate battery energy storage (LiFePO4 Energy Storage) is a new type of high-energy secondary battery emerging in recent years.

The electrochemical intercalation/deintercalation reaction principle is applied to realize the movement of lithium ions between the positive and negative electrodes. This process is essentially the process of current charging and discharging.

Lithium batteries are characterized by high energy storage density, small size, no pollution, low self-discharge rate, and fast charging and discharging speed. It has many advantages such as good power characteristics and is widely valued and welcomed by people. Although the lithium battery itself has certain shortcomings, such as: the battery price is higher than that of the lead-acid battery. However, from a comprehensive accounting point of view, lithium batteries will still be an important direction for the development of energy storage technology in the future. As the technology matures, the cost of lithium batteries will drop.

The composition structure of battery energy storage technology:

The energy storage system consists of battery, electrical components, mechanical support, heating and cooling system (thermal management system), bidirectional energy storage converter (PCS), energy management system (EMS) and battery management system (BMS). The batteries are arranged, connected and assembled into a battery module, and then fixed and assembled into the cabinet together with other components to form a battery cabinet. Below we introduce the important parts.

The energy type battery used in the battery energy storage system is different from the power type battery. Taking professional athletes as an example, power batteries are like sprinters. They have good explosive power and can release high power in a short period of time. On the other hand, energy-type batteries are more like marathon runners, with high energy density and can provide longer use time on a single charge.

Another feature of energy-based batteries is their long lifespan, which is very important for energy storage systems. Eliminating the difference between day and night peaks is the main application scenario of the energy storage system, and the use time of the product directly affects the project income.

Thermal management If the battery is compared to the body of the energy storage system, then the thermal management system is the “suit” of the energy storage system. Like people, batteries need to be in a comfortable temperature range (23~25°C) in order to work more efficiently. If the battery operating temperature exceeds 50°C, the battery life will decline rapidly. When the temperature is lower than -10°C, the battery will enter the “hibernation” mode and cannot work normally.

It can be seen from the different performance of the battery in the face of high temperature and low temperature that the life and safety of the energy storage system in the high temperature state will be greatly affected, while the energy storage system in the low temperature state will completely strike. The function of thermal management is to give the energy storage system a comfortable temperature according to the ambient temperature. As a result, the life of the entire system can be extended.

The battery management system can be regarded as the commander of the battery system. It is the link between the battery and the user, mainly to improve the utilization rate of the battery and prevent the battery from being overcharged and overdischarged. When two people stand in front of us, we can easily tell who is taller and who is fatter. But when thousands of people are lined up in front of them, the job becomes impossible. It is the job of the BMS to deal with this no-difficulty thing. Parameters such as “height, short, fat and thin” correspond to the energy storage system, which are three data of voltage, current and temperature. According to the complex algorithm, the SOC (state of charge) of the system, the start and stop of the thermal management system, the system insulation detection and the balance between the batteries can be inferred.