There are many types of flooded lead-acid batteries, which are used in photovoltaic energy storage systems. There are three types that are mostly used: flooded lead-acid batteries, valve-regulated lead-acid sealed batteries, and lead-carbon batteries.
The sulfuric acid in the electrolyte of the flooded-type lead acid battery directly participates in the battery charging and discharging reaction process. In traditional lead-acid batteries, the remaining space in the battery jar, except for the polar plates, separators, and other solid assembly parts is completely filled with sulfuric acid electrolyte, which is deep cycle flooded wet lead acid battery, in which the electrolyte is in a state of excess, so it is called a "flooded" battery with the battery polar plates completely immersed in the sulfuric acid electrolyte. There is a cover on the top of the flooded-type lead acid battery that can ventilate and prevent the liquid from splashing. During use, due to the evaporation and decomposition loss of water, the cover needs to be opened regularly to add distilled water and adjust the electrolyte density, so it is customarily called an "open type" battery. The flooded type lead acid battery has the characteristics of high power conversion efficiency, long cycle life, high terminal voltage, strong safety, high-cost performance, simple installation, maintenance, etc. It is currently the preferred chemical power supply in various energy storage, emergency system battery, and start-up devices.
They are also known as maintenance-free batteries, which can be divided into two types: AGM lead-acid batteries and gel-sealed lead-acid batteries. The AGM battery uses pure sulfuric acid aqueous solution as the electrolyte, most of which is in the glass fiber membrane, and a part of the electrolyte is absorbed inside the polar plate. AGM-sealed lead batteries have less electrolyte, thicker polar plates, and lower active material utilization than open-ended batteries, so the discharge capacity of the battery is about 10% lower than that of open-ended batteries. Compared with today's gel-sealed batteries, AGM-sealed lead batteries have a smaller discharge capacity. Gel-sealed lead storage batteries (ie GEL type batteries) and gel lead-acid batteries are improvements of the ordinary lead-acid battery with liquid electrolytes. It replaces the sulfuric acid electrolyte with the gel electrolyte, which improves the safety, storage capacity, discharge performance, and service life when compared with ordinary batteries. Its electrolyte is made of silica sol and sulfuric acid. The concentration of the sulfuric acid solution is lower than that of the absorbent glass mat battery, and the amount of electrolyte is more than that of the absorbent glass mat battery, which is equivalent to flooded batteries. This electrolyte exists in a gel state and is filled in the separator and between the positive and negative electrodes. The sulfuric acid electrolyte is surrounded by gel and will not flow out of the battery.
It is a capacitive lead-acid battery, which is a technology that evolved from the traditional lead-acid battery. It adds activated carbon to the negative electrode of the lead-acid battery, which is a flooded lead-acid battery for solar power, and it can significantly improve the lifetime of lead-acid batteries. Lead-carbon batteries are the most advanced technology in the field of flooded lead-acid batteries, and they are also the development focus of the international energy storage industry for new energy and have very broad application prospects. They are widely used in energy storage fields such as photovoltaic power station energy storage, wind power energy storage, and grid peak shaving.
When the flooded lead-acid battery is discharged, the metal lead is the negative electrode, which occurs in the oxidation reaction and produces lead sulfate; the lead dioxide is the positive electrode, and the reduction reaction occurs to produce lead sulfate. When the battery is charged with direct current, elemental lead and lead dioxide are generated at the two poles respectively. After removing the power source, it returns to the state before discharge to form a chemical battery. Lead batteries can be charged and discharged repeatedly, whose single voltage is 2V. The battery is a battery pack composed of one or more cells, referred to as a storage battery. The most common ones are 6v flooded lead-acid batteries, 8v flooded lead-acid batteries, and 12v flooded lead-acid batteries and there are other 2V, 4V, and 24V batteries.
The actual voltage of the storage battery is not a constant value. The voltage is high when there is no load, while the voltage will decrease when there is a load. When a sudden large current is discharged, the voltage will suddenly drop. There is an approximately linear relationship between the battery voltage and the remaining power. This simple association exists only when there is no load. When a load is applied, the battery voltage will be distorted due to the voltage drop caused by the battery's internal impedance. According to the battery voltage and the reference value of the remaining power of the battery, it is assumed that the voltage when the battery is fully charged is 12.8V. It can be known that the battery with a rated power of 12V when the voltage is 12V, the remaining power is about 50%; when the voltage is below 12V, the remaining power will drop rapidly.
The battery is bidirectional and has two states, flooded lead acid battery charging and discharging, and the current is limited. Different batteries have different maximum charge and discharge currents.
The charging and discharging current of the battery is related to the system. If it is not designed well, it will affect the performance of the system. Shallow cycle discharge helps to extend flooded lead acid battery life. The shallow cycle operation of the battery has two obvious advantages: first, the battery generally has a longer cycle life; second, the battery often retains more spare ampere-hour capacity, so the power supply guarantee rate of the photovoltaic system is higher. According to actual operating experience, the moderate depth of discharge is 60% to 70%.
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