Once the sun goes down or it gets cloudy, a solar system is only as good as the method used to store the harvested solar energy. Batteries are normally used as a power bank to provide the necessary storage to ensure the continuity of power supply by storing the surplus energy during the day. Battery capacity, power consumption, depth of discharge and round-trip efficiency need to be considered when choosing a battery for a solar power application.
Capacity is the total amount of electricity the battery can store. The power consumption and the depth of discharge (DOD) will affect the power storage plan and battery service life. The round-trip efficiency or energy conversion efficiency represents the ratio of energy put in versus the energy retrieved from storage. The energy plan should match the supply to the demand, and ensure the storage is sufficient to cover the periods when sunlight is not available.
Battery life is another factor to account for when choosing a battery. A battery with good cycle performance has much better economic benefit. The relative cost is lowered considerably, especially for applications in cycle use such as solar. Also, if the battery is installed in an environment without a temperature control system, a battery with a wider operating temperature range is better adapted to changes in ambient operating temperatures, resulting in prolonged battery life.
DIY or specialist installer?
For a small portable device or a home solar application, it may not be necessary to seek expert assistance. One could merely list the expected power consumption requirements and select the battery storage that is sufficient for the demand. Naturally, it is always important to follow the product installation instructions and make sure all the charging and discharging settings are correct and place the battery in a suitable working environment.
For a sizeable solar application, a specialist company is required to design a power solution to ensure that all details are taken into account. The battery solution might include not only the batteries, but also racks, temperature control system, online battery monitoring, etc. A battery management system (BMS) can also be beneficial; this typically comprises a more complete functional design to monitor the state of the battery in terms of voltage, temperature, charge, discharge, state of battery health, coolant flow and battery current. A BMS can also calculate the power requirements to adjust parameters dynamically, and implement a battery protection system to prevent the battery from entering an erroneous operation mode.
Maintenance and monitoring
A BMS is recommended for solar applications which should cover battery monitoring and protection features. However, a full-featured BMS is costly and may not be an option for consumers with a limited budget. Regardless, it is always recommended that the battery should be placed in an environment with temperature control, with the ideal operating temperature being between 20°C and 25°C.
Battery life might be reduced or the possibility of thermal runaway increased when operating at too high a temperature. In contrast, the discharge time will decrease if the battery is working at a lower temperature, and charging at a lower temperature may also shorten service life. Faulty procedures or inadequate charging methods, over-discharge, over-charge and insufficient charging time will result in failure to recover to normal capacity, reduced capacity, or shortened battery service life.
For solar applications, in particular, it is essential to know the power demand. The correct storage and charging plan is vital to avoid battery damage. It is also necessary to perform periodic maintenance for assurance of the optimum reliability of the battery if there is no battery monitoring or control system. Inspections can be conducted to identify a gradual decrease of the capacity of the system and to detect any abnormal error or individual battery conditions that may impact on system reliability.
Sealed lead-acid meets solar challenges
A sealed lead-acid battery is the least expensive battery option per watt-hour. The manufacturing process for sealed lead-acid batteries is a mature, reliable and well-understood technology. Sealed lead-acid batteries offer a wide range of capacity options for different applications and equipment. What is more, sealed lead-acid batteries have one of the lowest self-discharge rates in the family of rechargeable battery systems. This means they are not only economical, they also have two critical abilities – durability and dependability.
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