VRLA Batteries: usage in solar systems

VRLA Batteries, known as sealed or maintenance free batteries, are valve regulated lead acid batteries. VRLA battery types include gel batteries and AGM batteries.

Valve regulated lead acid (VRLA) batteries

A VRLA (Valve-Regulated lead acid) batteries are commonly known as sealed or maintenance free batteries. As the name ‘valve regulated’ defines, these batteries have a safety valve, which allows the release of gases produced. These batteries use recombinant technology for operations which means oxygen gas is produced on the positive plate and is absorbed by the negative plate. The negative plate produces hydrogen which combines with oxygen to produce water – this way the water content in the battery is maintained. VRLA batteries are of two types –

1. Gel batteries
2. AGM Batteries

Advantages of using VRLA batteries for your solar system

VRLA has numerous advantages over traditional flooded batteries.

• A flooded or wet cell battery utilises electrolyte as sulphuric acid which is a dangerous acid if spilled or externally comes in contact to anything. VRLA batteries don’t contain any such liquid, as their electrolyte is formed as gel and absorbed by separator sheets.

VRLA batteries are spill proof and can be installed in almost any location.

• Flooded batteries require proper ventilation set up for gas escaping, while valve regulated batteries allow for installation in places that have limited ventilation.

Common applications of VRLA batteries

VRLA batteries are used in many different industries, not just in solar:

Deep Cycle, Deep Discharge Applications

• Marine Trolling and Electronics
• Sailboats and Electric Vehicles
• Wheelchairs / Scooters and Golf Cars
• Portable Power and Floor Scrubbers
• Personnel Carriers and Renewable Energy
• Village Power (Solar, Wind)
• Marine & RV
• House Power Cycle Applications

Standby and Emergency Backup Applications

• UPS (Uninterrupted Power Supplies)
• Emergency Lighting
• Computer Backup
• Frequency Regulation (Solar, Wind)
• Telephone Switching

Other Applications

• Race -Highway Trucking
• Performance Cars and Off-Road Vehicles
• Diesel Starting and Light Trucks
• Start-Stop Systems

Charging of VRLA batteries

For charging of VRLA batteries two methods can be used –

• Constant Current which means that the output voltage of battery charge controller is varied keeping the current constant. This type of charging is suitable for batteries being used in cyclic applications as a traction battery and it is required that the charger is removed from the battery when the battery is fully charged.

Not suitable for stand by and emergency applications such as UPS, laptop and computer back-ups.

• Constant Voltage, which means same voltage is applied by varying the current throughout the charging of battery. Due to the potential difference between the charger and discharged battery, the initial currents are high, voltage varies and SOC increases. The initial charging of battery is quick but takes some time to get fully charged.

Overcharging or undercharging

As it is known that VRLA works according to the recombinant principle, charging above the limit causes excess oxygen and hydrogen production, which escapes through the safety or pressure relieve valve. This may lead to a dry condition in the battery. Since water cannot be added to the battery, this could lead to capacity loss or even permanent damage. If the battery is undercharged, the cell leads to sulfation. Sulfation is a phenomenon in which the sulphate from the cell goes back to the electrolyte during recharging of cells. Undercharging causes the sulphate retained on the cell plates causing reduction in capacity. In the long run this might cause cell failure. Keeping these two key points in mind and a little care will help the durability and longevity of VRLA Batteries.