Research and use of valve-regulated sealed lead-acid batteries in photovoltaic power generation

In recent years, valve-regulated sealed lead-acid batteries (VRLA) have become popular because they do not leak acid and do not corrode equipment and pollute the environment. They have been widely used in my country's telecommunications, electric power, and railway industries. Almost all of the batteries used in photovoltaic systems today are VRLA batteries. There are two important uses of VRLA batteries: (1) At night or under cloudy conditions and the output of the photovoltaic array is inconsistent with the load power consumption, the battery can store excess energy or supply energy to the load; (2) due to the work of the solar cell package The characteristics are greatly affected by solar irradiance, temperature, etc., and the load often cannot be located near the optimal operating point. The storage battery has the purpose of clamping the working voltage of the solar cell, which can ensure that the load is near the most ideal working point. Composition of photovoltaic power generation system Photovoltaic power generation system is a power generation system that uses the principle of photoelectric effect to convert solar energy into electrical energy. It is usually composed of solar battery packages, controllers, battery packs, and DC/AC inverters. The purpose of the solar battery package is to convert solar energy into electric energy to supply load to work or to charge the battery package; the purpose of the controller is to protect the charging and discharging of the battery package; the battery package is used to store electrical energy; the purpose of the inverter is to The direct current is converted to alternating current. At night or on a cloudy or rainy day, when the solar battery package cannot work, the battery pack will supply power to the load to work. It can be seen that the battery pack plays a very important purpose in the photovoltaic power generation system. Characteristics of VRLA batteries for photovoltaic power generation systems 1. The working mode of batteries for photovoltaic power generation systems. The working methods of batteries can be divided into two types: cycle use and floating charge use. It is often in the working state of frequent charging and discharging, that is, cyclic use; often in the charging state, it is used for floating charge, which can make up for the capacity loss of the battery due to self-discharge. VRLA batteries used in photovoltaic power generation systems are recycled. 2. Charging and discharging characteristics of batteries for photovoltaic systems. Generally, the charging and discharging characteristics of batteries for photovoltaic power generation systems have four points: (1) charging during the day, and discharging at night and in cloudy and rainy days; (2) the charging rate is low, and the average charging current is generally 0.01 to 0.02 C, rarely reaches 0.1 ~ 0.2C; (3) The discharge current is small, and the discharge rate is usually 0.004 ~ 0.05C; (4) A charge time is short, even if it is only about 10h in a long time. Photovoltaic systems rarely fully and quickly overcharge the battery, and the battery is often under-charged. 3. VRLA battery performance requirements for photovoltaic power generation systems. Photovoltaic power generation systems are mostly built in remote mountainous areas, plateaus, and Gobi. The natural environment is very harsh and the working environment temperature varies widely. Therefore, the batteries in photovoltaic power generation systems have the following requirements: (1) Deep-cycle discharge performance, long charge-discharge cycle life; (2) Strong overcharge resistance; (3) Strong capacity recovery after overdischarge; (4) ) Good charge acceptance; (5) When the battery is used in a static environment, the electrolyte is not easy to layer; (6) It has maintenance-free or low-maintenance performance; (7) It should have good high and low temperature charge and discharge characteristics; (8) It can adapt to the use environment in high altitude areas; (9) The batteries in the battery pack have good consistency. Photovoltaic power generation systems use lead-acid battery capacity design methods to determine battery capacity. First, determine how much power the load connected to the system needs every day; secondly, how many days of power the battery needs to store according to climatic conditions. When determining the capacity of a battery, it is not that the larger the capacity, the better. An excessively large battery capacity scale can also cause problems. This is because when the sunlight is insufficient, the battery pack may remain in a partially charged state. This under-charged state will result in increased battery sulfation, reduced capacity, and shortened life. The general calculation formula for battery capacity is Cu003dE·t/(D·η0·η1) (1) where C is the capacity of the battery; E is the average daily power consumption of the load; t is the longest hours without sunlight ; D is the permitted depth of discharge of the VRLA battery; η0 is the charge and discharge efficiency of the VRLA battery; η1 is the conversion efficiency of the inverter. The performance improvement of VRLA batteries for photovoltaic power generation systems. The failure and short life of the batteries are one of the reasons that hinder the promotion of photovoltaic power generation systems. The life of VRLA batteries will gradually shorten after being used in photovoltaic systems. The important factors affecting their life are: limited charging time, long-term undercharge; low current discharge; overcharge; temperature, etc. According to the special requirements of the photovoltaic system of the photovoltaic system for the battery performance, combined with the above factors that affect the battery life, a series of performance improvements have been made on the basis of the original VRLA battery. The detailed improvement measures include the following aspects: (1) Improve the cycle life. In order to extend the cycle life of VRLA batteries, the corrosion layer formed by the grid alloy at the interface between the grid and the active material should have good conductivity, and the grid should have creep resistance. The battery is designed to be tightly assembled, and the assembly pressure is appropriately increased. (2) Improve battery charge acceptance. For VRLA batteries, undercharging is more harmful to the battery than overcharging, so it is particularly important to improve the charge acceptance of VRLA batteries. Adding high-stability expansion agents and conductive additives to the negative lead paste formula improves the charge acceptance. (3) Improve over-discharge performance. Reduce the specific gravity of the sulfuric acid electrolyte and add special electro-hydraulic additives, which can reduce the corrosion of the electrode plate, reduce the initiation of electro-liquid stratification, and improve the battery's charge acceptance and over-discharge performance. (4) Use special safety valve. Regarding the plateau area, due to the low atmospheric pressure, the pressure value of the safety valve was specially adjusted.