The accumulator is a chemical power device that converts electrical energy into chemical energy through charging and stores it, and then converts chemical energy into electrical energy during use. It is made by immersing two separate electrodes in an electrolyte. The electrode made of the reducing substance is the negative electrode, and the electrode made of the oxidized substance is the positive electrode. When the external circuit is connected to the two poles, the oxidation-reduction reaction proceeds on the electrodes, and the active materials on the electrodes are respectively oxidized and reduced, thereby releasing electrical energy. This process is called a discharge process. After discharging, if there is a current flowing in the battery in the opposite direction, the two-pole active material can be restored to its original chemical state. Such reusable batteries are called secondary batteries or accumulators. If the reversibility of the battery reaction is poor, then after discharging, the charging method can no longer be used to restore the original state, this kind of battery is called a primary battery.
The battery is the energy storage device of the photovoltaic power station, which converts the direct current converted from the solar radiant energy into chemical energy and stores it for supply. The battery pack used with the solar cell array in the photovoltaic power station usually works for a long time under the semi-floating charging state. Considering the service life of the battery and continuous rainy days, the design capacity of the battery is generally 5~ of the daily power consumption of the electric load. 10 times, therefore, most of the time is in a shallow discharge state.
The basic requirements of solar photovoltaic power generation systems for batteries are: ① low self-discharge rate; ② long service life; ③ strong deep discharge capability; ④ high charging efficiency; ⑤ little or no maintenance; ⑥ wide operating temperature range; ⑦ low price. At present, the batteries used in supporting photovoltaic power generation systems in my country are mainly lead-acid batteries, especially valve-regulated sealed lead-acid batteries.
Lead-acid batteries were invented in 1859 after Gaston & Plante experimented with a large number of secondary batteries. They used two lead sheets as electrodes, and a thin spiral wound with rubber as a separator in the middle. They were immersed in a 10% sulfuric acid (H2SO4) solution to form a lead-acid battery. They found that this battery can be repeatedly charged and discharged, and observed that the lead-acid battery composed of lead electrodes in a sulfuric acid solution, when the primary current (charging current) is cut off, immediately discharges a strong current (secondary current ), which is obviously superior to batteries made of other materials tested. In 1906, Prandtl submitted a lead-acid battery composed of 9 single cells to the French Academy of Sciences. This was the world’s first lead-acid battery-Prandtl battery. Because its main raw materials are lead and acid, it is called lead-acid battery or lead-acid battery for short.
In 1881, Faure invented the paste-coated plate, but one of its serious defects was that the lead paste easily fell off the lead plate. In order to improve this situation, at the end of 1881, someone proposed a grid-shaped grid design, that is, the overall flat lead plate was changed to a porous grid, and the lead paste was stuffed in the small holes. This kind of electrode plate is better than the whole flat lead plate in keeping the active material from falling off. In 1882, a grid made of lead alloy was used to increase the hardness; in 1889, the shape of the slab was improved, and the shape of the grid was changed from a lead plate to a strip with a triangular section, which increased the lead paste and the plate. The contact area of the grid makes the lead paste tightly integrated on the grid, which greatly improves the performance and service life of the lead-acid battery. Lead powder, lead paste, and alloy grids have been determined as the plate structure of modern lead-acid batteries.
Since 1910, the production of lead-acid batteries has been fully developed. This is mainly due to two aspects: First, the rapid growth of the number of cars has led to the development of batteries used for starting, lighting and ignition; secondly, the use of lead-acid batteries in the telephone industry As a backup power source, it is required to be safe and reliable and can be used for many years, which makes the storage battery widely used in industries such as automobiles, railways, and communications. Subsequently, in 1957, the Federal German Sunshine Company made a colloidal sealed lead-acid battery and put it on the market, marking the birth of a practical sealed lead-acid battery. In 1971, the American Gates company produced a liquid-absorbing battery with a glass fiber separator, which is a valve-regulated sealed lead-acid battery (VRLA battery). From the market survey and forecast of lead-acid batteries, it can be explained that for more than 30 years of commercial application of VRLA batteries, although there have been some problems, such as leakage, early capacity loss, short life, etc., once aroused people’s suspicion of VRLA batteries. But after years of hard work, its design technology has been greatly developed. The development of lead-acid batteries has a history of nearly 150 years and is still full of vitality and vitality. The current total output value is about half of the total output value of all chemical power sources, and this share will continue to be maintained in the next 20 to 30 years.