What is a Solar Battery?

The solar battery is a part of an off-grid and hybrid solar system. It stores the excess electricity generated by solar panels.

An off-grid solar system first supplies electricity to run the appliance and then sends the excess power to the battery. 

On the other hand, a hybrid solar system sends the excess electricity first to the battery. When the battery becomes fully charged, it sends the extra electricity to the grid.

Why Do You Need Solar Battery in Off-Grid and Hybrid Solar System?

In the case of an off-grid solar system, solar batteries are a very important component as there is no connection with the grid. The main purpose of solar batteries is to store energy to run appliances during the night when the system does not generate power. 

However, hybrid systems stay connected to the utility grid. But still, why you will require a battery in a hybrid solar system? Solar batteries will make your system immune to power cuts and less energy production during cloudy days. When you are actually in need of more power, the battery will supply that for the smooth operation of your home appliances.

How Do Solar Batteries Work?

We have here explained how solar batteries work:

Function of Battery in an Off-Grid System

The excess energy that your appliances do not use goes from the inverter to the battery. The battery stores the energy as per its capacity. The stored battery powers your home appliances when the system does not generate electricity at night when the system generates less power during cloudy days or for some other reasons. However, when the battery is full, the excess solar energy gets wasted.

Function of Battery In a Hybrid Solar System

During the day, the solar panel in a hybrid solar system sends electricity for running appliances first, then the remaining power goes to the battery for storage. When the battery is full, your hybrid solar system will send the excess electricity to the utility grid. When the sun goes down, the battery sends the stored energy to the appliances. After the battery is completely discharged, the system draws power from the utility grid. The hybrid solar system comes with an additional net meter that keeps the record of imported/exported electricity to/from the utility grid.

Types of Solar Batteries

There are 4 main types of solar batteries available in the market. These are Lithium-ion, Lead-acid, Nickel Cadmium and Flow batteries. 

Lead-acid and Lithium-ion batteries are dominating the residential solar battery market. In the first few decades of residential solar adaptation, lead-acid batteries were heavily in use and they came at a quite cheap price as well. 

However, nowadays lithium-ion batteries have become the new standard in modern off-grid and hybrid solar systems. 

Nickel Cadmium and Flow batteries are majorly in demand for commercial purposes. This is because its technology is highly efficient, and the price is considerably higher. However, in the coming years, this might change which might reduce their prices. 

Let us take a detailed look at the four types of solar batteries majorly used along with their advantages and disadvantages

Lithium Iron Phosphate Batteries

The lithium-iron or li-ion battery is comparatively much newer in the solar energy category than Lead-acid batteries. It is quite common among residential solar users due to its long lifespan, lightweight and compact structure and less maintenance requirement. Plus, Li-ion batteries have a higher usable capacity as they can handle deep discharge of 80% or more.

Average Price of Lithium Iron Phosphate Battery: A 12V Lithium-iron battery may cost around Rs.30,000.

Advantages of Lithium Ion Batteries

The following are the advantages of using a Lithium-ion battery

  1. High Energy Density: In comparison to lead-acid batteries, lithium-ion batteries have a better energy density. This means that a lithium-ion battery takes less space to store an equal amount of energy in comparison to lead-acid batteries.
  2. Low Maintenance: Lithium-ion batteries require little to no maintenance. They usually work for years or decades without loss of efficiency.
  3. Long Warranty Period: These batteries have a warranty of approximately 5 to 10 years. Lithium batteries usually outlive other parts of the solar power system.
  4. High Discharge Depth: Due to its high depth of discharge, you can use more electricity than you produce and store before it has to be recharged.

Disadvantage of Lithium Ion Battery

Here are all the disadvantages of investing in Lithium-ion batteries

  1. High Price: They are comparatively more expensive than other storage technologies like lead-acid batteries. However, if you compare its lifespan then you will see that it costs less over time.
  2. Thermal Runaway: If you are unable to install the lithium-ion batteries properly there is a chance of thermal runaway. Thermal runaway can cause fire. However, if installed properly then the chance of catching fire is next to zero.
Lead Acid Batteries

The lead acid battery is the oldest type of solar battery. It can be a good option if weight and size are not a concern. They are most suitable for short-term applications. Lead acid batteries are available in both flooded and sealed. Sealed lead acid batteries are designed in order to reduce the release of toxic gases in the atmosphere while charging. The other type, flooded lead acid is a bigger version of the traditional car battery. In comparison to Lithium-ion batteries, lead-acid batteries are heavier, have a lower energy density and require regular maintenance. The average lifespan of the lead acid battery is 500-1000 lifecycle. Due to recent technological developments, its lifespan is improving it is still lower than lithium-ion batteries.

Average Price of Lead Acid Battery: A 12V 200ah lead acid battery may cost around Rs.24,000.

Advantages of Lead Acid Batteries

Following are the advantages of using a Lead-acid battery

  1. Low Cost: Lead-acid batteries cost less than most other types of solar batteries. However, due to the recent drastic drop in the price of Lithium-ion batteries, there might be a time when the price of Lithium-ion batteries might reduce more than that of Lead-acid ones.
  2. More Reliable: Lead acid batteries are comparatively more reliable as they have been existing for more than a decade now. Therefore the customers know what they can expect.
  3. Easily Disposable: Lead-acid batteries are easily disposable as well as recyclable.

Disadvantages of Lead Acid Batteries

Here are the disadvantages of using a Lead-acid battery

  1. Short Lifespan: As its lifespan is short, Lead-acid batteries need to be replaced multiple times in a lifetime.
  2. Low Lifetime: Depending on the type of lead-acid solar battery and its usage, a lead-acid battery might last between 3 to 5 years.
  3. Frequent Replacement: Though the initial price is lower, lead acid batteries require frequent replacement. 
  4. Ventilation Requirement: Flooded lead acid batteries need ventilation as well as regular maintenance in order to operate properly. There are also high chances of leaking in these batteries. 
  5. Low Depth of Discharge: Lead acid batteries have a lower depth of discharge, therefore they require more frequent charging.
Nickel Cadmium Batteries

Nickel Cadmium batteries are not quite popular for residential setups. Majorly, they are in use in large commercial operations such as airline and industrial requirements. Utility companies use this technology for the purpose of storing large amounts of energy. The nickel-cadmium battery is an older technology that came onto the scene for the first time in the 19th century. However, after the makeover in the 1980s, it became a more viable energy storage option for modern applications. Nickel Cadmium batteries operate in extreme temperatures. This is the reason behind their popularity among commercial-scale projects.

Average Price of Nickel Cadmium Battery: A 12V 200ah Nickel Cadmium Battery can cost around Rs.32,000. You may have to import it from China or other countries as it is rarely available in India.

Advantages of Nickel Cadmium Batteries

Following are the advantages of using Nickel Cadmium batteries:

  1. High Durability: Nickel Cadmium batteries are durable and long-lasting. It may have a lifespan of 20 years. This is the reason why it is so useful for the commercial sector.
  2. High Power Density: These batteries have a better power density in comparison to lead-acid batteries. Therefore Nickel Cadmium batteries can store more energy in a smaller space.
  3. Simple Battery Management System: Nickel Cadmium batteries do not require a complex battery management system and hardly require any maintenance.
  4. Smooth Performance in High Temperature:  As these batteries have the capacity to withstand extreme temperatures therefore you can store them in temperatures ranging between -65°C to 60°C.

Disadvantages of Nickel Cadmium Batteries

Here are the disadvantages of using Nickel-cadmium batteries

  1. Highly Toxic: These batteries are highly toxic because of the Cadmium present in them. Therefore, if you do not dispose of it properly, it might be dangerous for the environment. This is the reason many countries have banned the use of these batteries.
  2. Holding Charge: These batteries are also prone to memory effects. This effect reduces the ability of the battery to hold charge.
Flow Batteries

Flow batteries are new in the energy storage sector. In spite of being new, they are slowly becoming a popular option. These batteries depend on chemical reactions. It functions with water-based electrolyte liquid that flows between two separate chambers within the battery. A chemical reaction takes place within flow batteries to store the power.

Average Price of Flow Battery: A Vanadium Redox Flow Battery with 20KW/100kwh Capacity can cost around Rs.26 Lakh. You may import this type of battery as it is unavailable in India.

Advantages of Flow batteries

Following are the advantages of using flow batteries

  1. Complete Discharge: These batteries have 100% depth of discharge. This means you can use all the energy stored in the battery without damaging the battery’s health. The depth of discharge of this battery is the highest among all the four types of solar batteries present today.
  2. Non-toxic: These batteries are not toxic for being water-based. There is no risk of thermal runaway as the liquid present within the battery is fire retardant.
  3. Long Lifespan: It has the longest lifespan of up to 30 years which is the longest among all the four types.

Disadvantages of Flow batteries

Here are the disadvantages of using flow batteries

  1. High Price: The prices of these batteries are much higher in comparison to all four types of batteries. Therefore it is still quite an impractical option for households.
  2. Low Energy Density: Though these batteries have a high depth of discharge, the energy density is low. This means the tank in which the electrolyte liquid has to be quite large for storing a significant amount of energy.
  3. Large Size: Due to its huge size, it is not capable of household use.

Factors to Consider Before Purchasing Solar Battery

It is important to know which factors you should consider before considering which solar battery is best. Here you can find what you must look for while picking a solar battery for your requirement:

Capacity

A battery's capacity is the total amount of electricity it can store. Kilowatt-hours or Ampere hours is the unit of capacity of a solar battery. Not all solar batteries run at their full capacity. A standard capacity is 90%. If the capacity is 90%, you will be able to utilise only 9 kWh from a 10 kWh battery. You need to find out how much energy your solar panels will be able to generate in 24 hours as the storage capacity of a battery depends on this as well. Multiply the average output of your solar system by the number of days you need your battery to run non-stop without charging. The storage capacity of a battery also depends on the daily consumption of electricity.

Depth of Discharge

The depth of discharge is the amount of electricity you can discharge from the battery before in comparison to its overall capacity. Solar batteries retain some charge at all times so as to deliver optimum performance. If a battery has a depth of discharge of 90%, then a battery of 10 kWh will offer 9 kWh of power before you need to recharge it again.

Efficiency

Also known as round-trip efficiency, it is the percentage of usable energy that the battery delivers in comparison to the energy it takes. Therefore if a battery has a capacity of 10 kWh and you can utilise 8 kWh, then its round trip efficiency is 80%.

Lifespan

The lifespan of a battery generally ranges around 3 to 15 years. ] Proper maintenance is necessary to make sure the battery has the lifespan that the brand promises. It is best to keep your solar battery at standard room temperature for a better lifespan.

Warranty

The performance and capacity of solar batteries degrade as you continue using and charging them. This is why solar battery manufacturers offer a warranty that guarantees the optimum performance of batteries for a certain number of years.

Manufacturer/Brand

There are many brands that manufacture solar batteries. It is best to get the solar battery from a reliable brand that has been in the field for a long time. These brands are leading the industry as they provide the best quality products. Also, you should check the after-sales service from the brand.

Lifespan of a Solar Battery

Most solar batteries available in the market nowadays are anywhere between 5 to 25 years old. Following are the average lifespan of different types of batteries:

Battery Type Average Lifespan
Lithium-Iron Battery Up to 15 years
Lead Acid Battery Up to 5 years
Nickel Cadmium Battery Up to 20 years
Flow Battery Up to 25 years

There are certain factors like type of battery, usage, and environmental concerns like temperature, depth of discharge, and maintenance impact the longevity of a battery.

How to Install Solar Batteries?

The process of installing solar batteries is quite complicated and it is better if you leave this to professionals. 

Here are some steps that professionals follow to install solar batteries:

Step 1: Fusing of Solar System

Next comes the fusing of your system. You need to place one fuse between the positive battery terminal and the charge controller and another between the positive solar panel wire and the charge controller.

Step 2: Battery Connection with Charge Controller

Connect the solar battery to the charge controller with the battery cable. Connect the negative battery cable with the negative battery terminal and the positive battery cable with the positive battery terminal. After connecting, switch on the charge controller to check whether you have connected the battery properly. After this, program the charge controller according to the battery type, voltage etc.

Step 3: Connection of Solar Panel with Adapter Cable

Next is connecting the solar panel to the charge controller with MC4 solar adapter cables. Most solar panel cables come with pre-attached MC4 connectors and negative cables with MC4 adapter cable. After this, check whether the charge controller is turning on to make sure whether the panel is working properly.

Step 4: Final Testing of Battery Connection

Finally, check whether the battery is working properly by putting your solar panel in direct sunlight. When you do so, the charge controller should indicate that the battery is charging. The charge controller stops charging the battery when it is full. It is important that solar panels do not connect to the batteries directly as it might cause damage. You need to connect both the battery and the solar panel with the solar charge controller that regulates the amount of amperage and wattage passing on to the battery.

Frequently Asked Questions

If you continue using the batteries at high temperatures it will affect the longevity of the battery as well as damage it. Even if you try using batteries at very low temperatures, their efficiency will reduce. If the voltage is too high, the batteries might become heated, resulting in the release of hydrogen gas which is irreversible.

When the battery is full, the charge controller stops electricity flow. This is necessary as overcharging damages a battery’s life.

Though it is very unlikely but yes there may be a point when your solar batteries might be too hot to touch. This might be due to some manufacturing defect as a result of which your battery malfunctions.

Though it is unlikely that a battery will reach a temperature that exceeds its operating range. However, it might get to the point that the battery might explode. Therefore if you notice some bubbling, bulging, gas emission, sparks and flames in your battery it is best to remove the battery connection to your home or the grid.

The ideal place for placing your solar battery is in the house and close to the consumer unit. Some examples of such places might be a hall cupboard, utility room and under-stairs cupboard. However, if these are not available you can also place them in the garage.

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