Electrical energy plays a significant role in industrial development, urbanization, and economic advancement, as well as in our daily life. Electrical energy generation around the world is undergoing significant changes to solve the problem of imbalance in power generation and utilization, and to solve the problem of developing renewable energy to cope with climate change and energy supply shortage. However, there are several energy storage systems, including hydroelectric power, capacitors, compressed air energy storage, flywheels, and electric batteries.
Especially, electric batteries exhibit considerable potential for application to grid-level electrical energy storage with their attractive features, such as flexible installation, modularization, rapid response, and short construction cycles. When electric batteries are applied to the energy storage system, battery technologies are required to satisfy complex and large-scale deployment applications to the power grid.
Applications of Lithium-Ion Batteries in Energy Storage Systems
--Frequency Regulation and Peak Shaving
Frequency regulation has high requirements on the energy storage system, which needs to meet fast response, high rate performance and high power capability. Therefore, this is a challenge for the battery. It is necessary to consider voltage stability and frequency stability, as well as short-term and long-term applications. Lithium-ion batteries have the characteristics of high discharge/charge efficiency, high specific energy, and long cycle life. It has considerable application potential.
--Renewable Energy Integration
Renewable sources is abundant and widely distributed in the grids of many regions, making it one of the most cost-effective options for generating electricity. The substantial growth of variable renewable energy sources in recent years has spurred the development of electrical energy storage systems and required them to be more flexible. The battery energy storage system can effectively store the electric energy generated by renewable energy, contribute to the stability and reliability of the grid system, and thus promote the use of renewable energy.
Wind power generation is greatly affected by seasons and geographical locations, considerably suffers from intermittence, and there is often a mismatch between peak power generation and demand. Storing excess energy generated by wind farms and supplying electricity during peak periods is an effective solution.
In the same way, solar photovoltaic power generation is affected by night and weather, but it can forms a perfect operating system when combined with the battery, which can cope with high gradient power spikes and steady-state power demand. The use of batteries in a solar photovoltaic field exhibited output power stability, particularly under partial shading and solar radiation
Despite the high energy density of lithium-ion batteries, a single cell is insufficient to meet the requirements of the grid. Therefore, the batteries need to be assembled in parallel to increase the current capability or in series to increase the voltage, which poses serious challenges to the stability, voltage operation, safety, and cycle life. For example, with just a few cells in series, the charge current and voltage are divided nearly equally among the cells. However, to achieve a high voltage, many cells need to be connected in series, which will result in unevenly divided voltage among these cells, leading to unbalanced cells with some cells fully charged and others overcharged. Lithium-ion battery do not deal well with overcharging, resulting in potential safety issues and limited cycle life of the system. Therefore, establishing a system monitor to prevent any cell from being overcharged and balance the batteries to maximize the performance of the entire system is essential. To ensure safety, the lithium-ion battery monitors must function as follows: (1) balance the circuit and prevent the voltage or current of any cell from exceeding the limit by stopping the charging current, which should be considered to address the safety issues and ensure the stability of the system, and (2) monitor the temperature and prevent the temperature of any cell from exceeding the limit by requesting that the system be stopped and cooled.