- Lead acid battery
Since the input energy of solar photovoltaic power generation system is extremely unstable, it is generally necessary to configure energy storage device (battery system) to work. The most suitable energy storage method for electric energy generated by photovoltaic power generation is to convert electric energy into chemical energy, which can be converted into electric energy when needed. Lead acid battery is the best device that can effectively complete this conversion at present
Because the positive electrode of the battery is lead oxide, the negative electrode is lead, and the electrolyte is mainly dilute sulfuric acid, it is also called lead-acid battery. Lead acid battery has become the largest and most widely used battery in the world because of its long-term storage, high energy, high current discharge, low price, easy availability of raw materials, reliable performance, easy recovery and low maintenance cost. Lead acid battery has been widely used in solar power plant system, electric vehicle, automobile, communication, electric power, railway and other fields In order to better play the role of photovoltaic power generation system in installation, use and maintenance, we should understand the photovoltaic power generation energy storage device
- Classification of lead-acid batteries
According to the structural form of products, they can be divided into open type, rich liquid maintenance free type, glass wool diaphragm adsorption valve controlled sealing type (AGM), valve controlled rubber type and so on. China’s lead-acid batteries are mainly adsorption and colloid batteries. At present, AGM adsorption batteries dominate the market
Although colloidal battery has the advantages of good discharge performance, hard bending of plate and long service life, due to the difficult production, high technical level, unstable colloidal materials and high production cost in China, there are only a few battery factories in production in China, and users report that the product quality has not been significantly improved. According to the report of authoritative battery research institutions abroad, the comprehensive technical index and service life of colloidal dynamic battery are significantly better than ordinary AGM adsorption battery. Colloidal battery is the development direction of dynamic lead-acid battery. The products of lead-acid battery are shown in Figure
- Composition of lead-acid battery
Lead acid battery is composed of positive plate, negative plate, separator, battery tank and electrolyte.
(1) Positive plate anode refers to the electrode with oxidation reaction. The anode plate of lead-acid battery is the positive electrode. It uses fine crystalline, loose and porous lead dioxide as the active material for storing electric energy. It is normally red. Each unit of lead-acid battery is also divided into positive and negative. The anode is the negative electrode when discharging and the positive electrode when charging.
(2) Negative plate (cathode) negative electrode refers to the electrode with reduction reaction. The negative plate is the positive electrode during discharge,
Negative electrode during charging. The negative electrode (cathode plate) uses sponge like metal lead as the material for storing electric energy, which is normal
(3) The separator is made of a material that prevents the penetration of ions, which can prevent between ions with opposite polarity in the battery
Contact components. The positive pole and negative pole of the battery are separated by a partition, and the partition of the adsorption sealed battery is
It is made of ultra-fine glass wool. This kind of separator can adsorb the electrolyte in the separator. The name of adsorption sealed battery comes from this.
(4) Battery trough, hard rubber type and plastic trough.
(5) Electrolyte contains mobile ions and liquid or solid substances with ionic conductivity, which is called electrolyte. The role of electrolyte in lead-acid battery is:
① Participate in electrochemical reaction;
② Conductor of positive and negative ions in solution;
③ The plate produces a thermal dispersion of temperature.
- Basic concept of lead-acid battery
(1) The operation that the external circuit of battery charging supplies power to the battery to make the chemical reaction in the battery, so as to convert the electric energy into chemical energy and store it.
(2) Overcharge continues to charge a fully charged battery or battery pack. The capacity of the battery under the specified discharge conditions. The unit is usually expressed in ampere hour (a · h).
(3) Discharge the process in which the battery outputs electric energy to the external circuit under specified conditions.
(4) The energy of self discharging battery enters the external circuit without discharge. This phenomenon of energy loss is called self discharge.
(5) Active substances are substances that produce electric energy by chemical reaction when the battery is discharged, or substances that store electric energy in the positive and negative electrodes are collectively referred to as active substances.
(6) Discharge depth refers to the extent to which the discharge of the battery begins to stop during use.
(7) When using lead-acid battery, special attention should be paid to plate vulcanization: the battery should be charged in time after discharge. If it is in the case of half discharge or insufficient charging, or even overcharging for a long time, or charging and charging for a long time
PbSO4 crystal will be formed during discharge. This large crystal is difficult to dissolve and cannot be restored to its original state, which makes it more difficult to charge after plate vulcanization.
(8) Relative density the so-called relative density refers to the ratio of the density of electrolyte and water, which is used to test the strength of electrolyte. The relative density is related to the change of temperature. At 25 ℃, the relative density of fully charged battery electrolyte is 1.265. For sealed batteries, the relative density of electrolyte cannot be measured. The density of pure acid solution is 1.835g/cm3, which decreases to 1.120g/cm3 after complete discharge. After the electrolyte is injected with water, the density can be measured accurately only after the water is completely fused with the electrolyte. The integration process takes about hours or days, but the time can be shortened by charging. The electrolyte density of each battery is different, even if the same battery has different electrolyte density in different seasons. The density of most lead-acid batteries is between 1.1 ~ 1.3g/cm3, which is generally 1.23 ~ 1.3g/cm3 after full charge. Liquid densitometer is often used to measure the relative density of electrolyte. The relative density of electrolyte will also be affected for batteries at high or cold temperatures. This situation is usually indicated on the battery. The efficiency of the battery is affected by the discharge current. Therefore, the decrease of efficiency caused by large discharge current output and the impact on the service life of the battery should be avoided.
(9) Operating temperature: the battery feels hot after being used for a period of time. Therefore, it can be seen that the lead-acid battery has strong heating. When the operating temperature exceeds 25 ℃, the service life of lead-acid battery will be reduced by 50% for every 10K increase. Therefore, the maximum operating temperature of the battery should be lower than the outside world. It is best when the temperature change exceeds ± 5K. If temperature compensation charging measures are taken, the battery temperature sensor should be installed on the anode and insulated from the outside world.
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