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What are Solar Batteries and How Do They Work?

Written by Nigel Engelbrecht

Solar batteries have advanced rapidly over the last 10 years. That which was leading a few years ago is no longer the case. We have the incumbents such as lead acids and AGM batteries battling it out with the new entrants, namely Lithium. This article seeks to explain how solar batteries work, the differences in tech, and hopefully help you make the right choice for your solar project!

When it comes to most renewable energy systems, storage is important. Storage is achieved by using batteries and there are several battery options available on the market. Below are the most common:


Arguably the longest-standing battery and most widely adapted to many applications. From military use to boats and also renewable energy systems. Lead acid batteries are, as you probably guessed, made up of a lot of lead. They tend to require some careful maintenance, but other than that they are strong, sturdy and do the job.

Source: Doitpoms

Lead acid batteries have been around for a long time, but few technological changes have been made. They have become more efficient, but lead is the key factor in them for many years now. 

There are many lead acid battery suppliers and most of them are very similar in what they offer, including pricing. They are readily available and require little setup knowledge to get them working.


Absorbed Glass Mat (AGM) batteries are a variation of lead acids, but they have a somewhat different composition. AGM batteries contain a very fine fibreglass mat that absorbs sulphuric acid, making them more efficient and maintenance-free. However, they are more expensive than their older cousins the lead acids, but they promise better performance – especially in energy systems.

Like lead acid batteries, AGM batteries come in various sizes, but mainly in 12v ranges. This means you need to ‘stack’ them in series to achieve the required voltage for them to operate optimally – 24 volts or 48 volts is the most popular voltage range for residential homes. 

AGM batteries are readily available and simple to get running. 


When it comes to lithium batteries, there are several chemistries and manufacturers. However, for the sake of this article, we will focus on the two main lithium types being used in South Africa. 

Famous brands using this chemistry are Pylontech and Dyness. Many suppliers of lithium batteries use this chemistry and rename them under license. 

Lithium batteries require some technical knowledge to set up and troubleshoot, so it’s best to get a solar installer and/or electrician to install these in your home. Like lead acids and AGM’s, you can have 12v, 24v and 48v lithium versions to suit your needs.

Lithium batteries are intelligent batteries as they have BMS’ (battery management systems) either built into or external to the battery. The BMS regulates and maintains the battery aspects like voltage, discharge, and temperature.  


Like lithium polymer, a lithium phosphate battery has a BMS and built-in intelligence, allowing it to be ‘maintenance free’ and safe. However, where polymer-based lithiums are subject to heat degradation and overvoltage – which can cause them to catch on fire – the phosphate chemical version is currently the safest. 

Lithium phosphate batteries are more expensive than their polymer cousins but are safer and more stable with energy use and storage. LiFePO4 batteries are gaining in popularity due to their robust long life and safety tolerance.

Popular brands of the LiFePO4 batteries are the BSLB lithium, Solar MD, and Hubble series of batteries. All excellent quality and long-lasting.

To make your life a little easier, we put this handy comparison table together:












R2 500,00






R4 000,00



1/ 2 YEAR



R19 000,00


>4000 CYCLES

3 – 5 YEARS



R25 000,00


>5000 CYCLES


While this table is in no way comprehensive, it serves as a basic starting point for you to base your decisions on for your energy storage needs. While many different types of lithium batteries will come available in the years ahead, these two will remain the most popular for the foreseeable future.


There are several important considerations when deciding on which batteries you require, and this is best left to the professionals. However, it doesn’t hurt to know a little self-empowering information. So here are some pointers:

  • Your battery bank should be at least 10% more in KW than your installed inverter
  • Battery warranties differ, get it in writing
  • Pay attention to heat restrictions in warranty clauses
  • Gel and lead acid batteries allow for on average 60% of their capacity
  • Lithium batteries allow for up to 80% capacity
  • If buying lithium, make sure your installer understands the floor and ceiling levels relating to charging before installation 
  • Ensure you understand the difference between 0.5C and 1C rated batteries. 

When searching online for batteries, always make sure you understand the amperage performance of the battery. Amps are the allowable capacity, not kW. When sizing or researching batteries, look for the voltage, kW, and amperage, for example:

51v 5,1kW [100Ah] BSLB lithium battery @1C

  • 51v—volts 
  • 5,1kW—kilowatts 
  • 100Ah—amperage 
  • 1C—performance rated

Therefore, this battery is a true 5,1kW, meaning you take the 1C x 100Ah = 100Ah. However, a 0,5C will instead be 0.5C x 100Ah = 50Ah

Amperage or C ratings will be available on either the datasheet or warranty conditions. In this example, you need 2x 0.5C rated batteries to produce the power of the 1C rated battery. 

Cycle ranges differ on different batteries, so make sure you know what those are. Cycles give you an indication of the useable ‘life’ of the battery. A simple formula is used:

3000 cycles / 365 days = 8,2 years of life calculated at 80% DoD.

DoD, also known as depth of discharge, varies from battery to battery, but this is used to measure the useful life of a battery over a percentage period of use. In other words, if you use a battery at say 80% only, you will get X amount of years. Again, pay attention to heat clauses in the warranty. Heat is the number one enemy of batteries. 

There is a lot more information available on batteries, but this article should give you enough details to make some educated decisions.

Thank you for reading this article. If you feel we have left out any important information or would like to contribute to this site and content, please get in touch with us by leaving a comment or emailing us directly.


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