Choice of Battery is very important if you are planning to have energy storing option for your system to use a sa backup. But every battery are not the same and certainly do not perform the same. Knowing the different categories and types of battery is not sufficient to select a battery for a given requirement.
The selection of a battery is done by seeing the battery parameters. The parameter values for voltage rating, current, capacity rating, number of charging-discharging cycles and self life differs from battery to battery. These values also differ from one manufacturer to another. So, we must have good understanding of the battery parameters to identify a proper battery for an application before buying or using it.
In the market, many types of batteries are available. While designing a solar PV system comprises of batteries, the one problem often faced is a proper choice of battery from many available batteries. This problem can be simplified by making a list of minimum requirements, conditions and limitations we have.
Based on the application, the type of a battery is chosen. For example, primary batteries are used in portable devices which run on very low current, such as electronic watches, torch, and radio. Primary batteries are used for one time only. They are cheap and easily disposable.
Some applications require high current to run the devices. In such cases, the secondary batteries or rechargeable batteries are used which provide high current as they have high capacity and can be recharged a number of times. The rechargeable batteries are costly compared to other primary batteries, but they are cost effective over long run.
Voltage and Current
A battery should be selected according to the voltage and current requirements of the instrument to which it is connected.
The batteries are designed to operate at certain temperature, normally about 25 degree centigrade. In practice, the prevailing temperature or ambient temperature may be different. Sometimes, the ambient temperature can be above 45 degree centigrade or below freezing temperature. Her we should remember that the battery output and its capacity depends on the temperature.
At higher temperature, batteries can deliver higher current compared to lower temperature. At lower temperatures, like below 20 degrees centigrade, the chemical reaction inside the battery slows down and the battery gives lower current value than the designed value.
At higher temperature, the battery may provide higher current than designed value, but its self-life decreases significantly. At very high temperatures, some batteries explode posing life threat. Therefore, depending on the operating temperature of battery, appropriate battery mus be chosen for a given application. The manufacturer datasheet provides the information about safe operating temperature and how the capacity and current will change with temperature for a given battery.
Battery Self Life
Batteries self life is directly affected by the rate of self-discharge. Self discharge occurs all the time, even the battery is not used. Some batteries have extremely low self-discharge rates, such as most of the lithium battery whereas, some nickel metal hybrid batteries can lose upto 4% of their capacity every day.
The number of charge-discharge cycle of a battery depends on the type of battery. Normally, for rechargeable applications, battery with large number of charge discharge cycle should be chosen. For instance, for standalone solar PV systems batteries with large number of charge-discharge cycles are chosen.
Cost of Batteries
Costing of batteries is based on the type of batteries selected and it’s pricing by different manufacturers. also, it depends on the features of the battery. Generally, the maintenance free and advanced technology batteries are expensive. So, normally the efforts are made to optimize the battery requirement and reduce the cost. In some cases, it may require that system must perform in all conditions, therefore, the over sizing of the battery is done. In such cases, the cost of battery is not important but the reliable system performance is given importance. but if the system requirement is not crucial, then we should try to minimize the battery expenses in a PV system.
Availability of batteries
Before selecting a battery, we should check its availability in the market. If a battery, rarely available, is used in a system, it may create problems while replacing or buying a new one for the system. So , a battery that is readily available, easy in transportation and can be bought even in remote places, should be selected.
The choice of battery can be the real deal maker or the deal breaker for your next project. So make the right decision.