This Is What You Need To Know About Home Solar Batteries

The batteries that you know today are a result of years of experiments and science. In the year 1800, Alessandro Volta, an Italian Physicist, invented the first working electrochemical battery. The battery used copper and zinc plates soaked in salty water to generate a potential difference of 0.76 volts across the cathode and anode terminals. The battery was working, yet it was not ready for mass production until two years later.

All the rechargeable devices owe it to French physician Gaston Planté who invented the first rechargeable battery. When talking about solar power, ‘off-grid’ solar power or photovoltaic systems need at least one battery to store the electric current. The batteries used in PV systems are rechargeable, which means that you can charge and discharge them several times. As far as the PV systems connected with a utility grid concern, they are on-grid, thus do not need batteries.

Here, we will cover the most common types of PV battery technologies and learn about the differences and similarities between them. Also, let’s understand some of the pros and cons of each type of battery, as the knowledge will come handy when buying a PV battery.

Batteries based on the difference in construction Flooded Batteries

Flooded batteries, as the name suggests, come with liquid electrolyte solutions held free to move inside a plastic container. These mimic the design of the original electrochemical battery, thus also known as ‘wet-cell’ batteries. Flooded batteries are suitable for use in off-grid applications, as they are deep-cycle batteries.

Advantages of flooded batteries

• Flooded batteries come with 70-80% depth of discharge (DOD). Thus, they are capable of deep discharges without getting damaged.
• These batteries are available on an economical budget.

Disadvantages of flooded batteries

• Flooded batteries need a routine check.
• It is crucial to measure and maintain the electrolyte solution inside flooded batteries.
• There are chances that a Flooded battery can damage from forceful movements.
• Extreme climatic conditions can reduce the life of flooded batteries. The electrolyte inside a flooded battery can dry in hot and freeze in cold temperatures, reducing its capacity.
• Flooded batteries need proper ventilation to get rid of the gases and to stay cool.

Sealed Batteries

The  1970s were when the first sealed batteries developed. These batteries do not contain a freely-moving liquid electrolyte. Instead, they use immobilization techniques to hold the electrolyte between layers of metal plates. Thus, these are also known as ‘captive electrolyte batteries.’ A valve on the sealed batteries allows the venting of gases during the charging and discharging operation.

Advantages of sealed batteries

• Do not need regular checks.
• Provide up to 5 times fast charging in comparison with the flooded batteries.
• Sealed batteries do not need regular water or electrolyte filling.
• These batteries are ideal for placing in different positions, as there is no risk of the electrolyte spilling out.
• They are suitable for use with stand-alone PV systems.

Disadvantages Of Sealed Batteries

• The sealed batteries provide limited deep charges.
• Over time, the electrolyte can lose contact with the metal plates, resulting in a decrease in the performance of the sealed battery.

What holds the electrolyte inside a sealed battery?

There are two types of sealed batteries, and they use substrates that captivate or immobilize the electrolyte.

Gel Electrotype Sealed Batteries

In the gel sealed batteries, the sulphuric acid (electrolyte) immobilizes in silicon oxide. When a molten mix of silicon oxide and sulphuric acid cools down, it forms a gel electrolyte. Paths and voids for the movement of gases form as the gel dries out.

Absorbed Glass Matt (AGM) Sealed Batteries

In AGM type sealed batteries, the sulphuric acid (electrolyte) immobilizes on thin absorbent fiberglass matt. Electrode plates in an AGM type battery get a regular supply of electrolyte from the saturated electrolyte matt. The fiberglass matt also acts as a separation between the electrode plates.

Batteries based on different electrodes

Small batteries in cell phones, the ones that you use in the car or inverter, and the battery for a PV system; all may have a different electrode and electrolyte solution. Based on the electrode and electrolyte composition of a battery, it can provide a higher or lower ‘energy density.’ Two c common  types of rechargeable batteries available for PV systems are:

Lead-Acid batteries

Lead-Acid types are the oldest forms of rechargeable batteries. Such batteries use strips of lead (electrode) and a diluted solution of sulphuric acid (electrolyte). These are also the most common types of batteries, popular among industrial, commercial, and residential users. Lead-acid batteries can last up to 3 to 5 years, as they are known for standard deep cycles.

Lithium-ion batteries

Lithium-ion batteries (LIB) are standard in electronic devices such as cell phones, computers, and other consumer electronics. In general, the LIBs found in electronic devices will have cobalt oxide electrodes with sodium lithium electrolytes. LIB batteries for PV systems use lithium iron phosphate (LFP).  These batteries provide a high energy density of up to 150 watt-hours per kilogram.

What is the Difference between Flooded Lead-Acid and Sealed Lead-Acid Batteries?

• The apparent difference between sealed and flooded type Lead-acid batteries is their construction. Flooded Lead-acid is not as expensive as sealed lead-acid batteries.
• Sealed acid-batteries are ideal for use in places sensitive to gases that emit during charging and discharging.
• Flooded batteries are suitable for use in heavy-duty applications, as they allow manual monitoring of the electrolyte.

What should one look before buying a battery?

Residential solar batteries offer set capacities that measure in kiloWatthours (kWh). Whether to choose a flooded or sealed battery depends on the usage and budget of an individual. However, one must keep an eye on the following parameters:

Power Rating

The power rating of a battery determines the amount of electricity it can provide at a given moment. Battery manufacturers mention the power ratings in kilowatts. A battery with high capacity and low power rating will provide lower electrical output for a long time. In contrast, a battery that has a small capacity and high power rating will provide higher electrical outputs for a shorter time.

Depth Of Discharge

The Depth of Discharge or DOD is the level up to what you can discharge or use a battery. If a 10KWh battery has a DOD of 90%, you should not discharge/use it any further than 9KWh.

Round- Trip Efficiency

The round-trip efficiency is the measure of how efficient the battery is while charging. If a battery takes 5KW of the electrical input to store 4KW of electrical charge, its round-trip efficiency will be 80%. It would be best if you look for batteries that offer a higher round-trip efficiency.

Battery Lifespan

Whether rechargeable or not, every battery decomposes at some point in time. However, it would help if you always choose batteries that offer more ‘cycles.’ A cycle is the combination of both the charging and discharging the battery. Buying a battery that provides more cycles will mean that the battery will last longer.