Selection and calculation of battery

【Abstract】

The storage battery is one of the main components in the off-grid photovoltaic power station. Its main function is to store energy and convert the electrical energy provided by solar cells into chemical energy for storage. Generally, the battery pack is charged by the solar cell array during the day, and the load is supplied by the battery pack at night, and the battery is in a semi-floating charging state. In the actual operation of off-grid photovoltaic power plants, the normal operation of the entire system is often affected by battery failure. Therefore, when designing an off-grid photovoltaic power station, it is very important to select the appropriate battery type, capacity, and correct installation, operation and maintenance for the normal operation of the off-grid photovoltaic power station.

【Text】

Commonly used battery types in off-grid photovoltaic power plants

1. Lead-acid maintenance-free battery

The biggest feature is "maintenance-free". Compared with lead-acid batteries, the consumption of electrolyte is very small, and there is basically no need to supplement distilled water during the service life. It also has the characteristics of shock resistance, high temperature resistance, small size and low self-discharge. In contrast, its price will be more expensive than lead-acid batteries. As for the service life, the recommended replacement period for maintenance-free batteries under normal conditions is about 3 years, which is equivalent to lead-acid batteries.

2. Ordinary lead-acid batteries

The battery was invented by the Frenchman Plante in 1859 and has a history of more than 100 years. The battery is mainly composed of tubular positive plate, negative plate, electrolyte, separator, battery tank, battery cover, pole post, liquid injection cover, etc. The main advantages are stable voltage and low price; the disadvantages are low specific energy (that is, the electric energy stored per kilogram of battery), short service life and frequent routine maintenance. Old-fashioned ordinary batteries generally have a life span of about 2 years, and it is necessary to regularly check the height of the electrolyte and add distilled water. However, with the development of technology, the life of lead-acid batteries has become longer and maintenance has become easier.

3. Gel battery

The colloidal lead-acid battery is an improvement of the ordinary lead-acid battery with liquid electrolyte. It replaces the sulfuric acid electrolyte with the colloidal electrolyte, which is better than ordinary batteries in terms of safety, storage capacity, discharge performance and service life. There is no free liquid inside. Under the same volume, the electrolyte capacity is large, the heat capacity is large, and the heat dissipation ability is strong, which can avoid the phenomenon of thermal runaway in general batteries; the electrolyte concentration is low, and the corrosion effect on the electrode plate is weak; the concentration is uniform and there is no electrolysis Liquid stratification phenomenon.

4. Alkaline nickel-cadmium batteries

Nickel-cadmium battery (Nickel-cadmium battery) An alkaline battery in which the positive active material is mainly made of nickel and the negative active material is mainly made of cadmium. The positive electrode is nickel hydroxide, the negative electrode is cadmium, and the electrolyte is potassium hydroxide solution. Its advantages are lightness, shock resistance, long life, and are often used in small electronic equipment. Nickel-cadmium batteries can be charged quickly and have a long cycle life. It is more than twice that of lead-acid batteries and can reach more than 2,000 times, but the price is 4 to 5 times that of lead-acid batteries. Although its initial purchase cost is high, its long-term actual use cost is not high due to its advantages in energy color and service life. However, recycling must be done during use, otherwise the heavy metal cadmium will pollute the environment.

Capacity design of battery pack for off-grid photovoltaic power station

The battery pack is the part with the shortest service life in the off-grid photovoltaic power station.

It will be updated after a certain period of time. In Qinghai Province

Capacity design of battery packs for off-grid photovoltaic power stations in the "township" project

At the time of selection, we fully considered high altitude and alpine regions

Area, temperature characteristics, plateau low pressure environment, etc., selected

GFM series valve-regulated sealed lead battery.

In Qinghai Province’s "Electricity to the Township" project, in off-grid photovoltaic power plants

The rated working voltage of the system is 220V, and the battery cell rated voltage

For 2V, 110 single batteries can be connected in series.

Obtain a working voltage of 220V. Use multiple battery packs in parallel

Way to meet the design capacity of the battery pack of the power station.

The calculation formula of battery capacity is:

c-Q·D.K

nim z·S

In the formula: Q——daily power consumption (kWh);

D——Support days (generally 3~5d);

Inverter efficiency (take 0.92);

-Battery charge and discharge efficiency (take 0.85);

2

K-temperature correction coefficient (take 1.2);

S——Discharge depth (usually 60%~70%).

According to the above parameters, the battery pack of off-grid photovoltaic power station can be determined

【Conclusion】

When selecting batteries, it is very necessary to understand the differences between the processes and the use of various batteries. First of all, we must fully understand the needs of the users themselves. For example, the capacity requirements of the backup power system, the frequency of use, the environment of use, the main purpose, the service life, the reliability requirements, the instantaneous discharge rate, the specifications of the rectifier, and other battery-related performance requirements. Secondly, it is necessary to understand the electrical performance of the battery, including product design parameters (battery model, appearance size, rated capacity, rated voltage, weight, weight ratio energy, volume ratio energy, design life, number of positive and negative plates, positive and negative plates Thickness ratio, electrolyte density, plate type, grid material, etc.), product electrical performance parameters, product actual service life, installation and use environment, performance and price of different models, and warranty periods for different types of products.