Solar Power for Dummies part 4: The Batteries


If you ask anyone with a Solar Power system what the most vulnerable part of their system is, you will no doubt be told it’s the batteries.

Batteries are perhaps the most delicate part of any off the grid solar system and while your solar panel is going to last for eons, it is unlikely going to be the case with your batteries. They are a constant source of headache and grief especially if you make mistakes during the buying and installing process.

Batteries perform the same function for electricity that a tank does for water. They store electrical energy in a chemical form that will be utilized during the periods when the panels are not charging. They also act as a reservoir of sorts to provide a stable source of power during the charging periods when there is a constant flux in the amount of charge coming from the panels


They also act as a reservoir of sorts to provide a stable source of power during the charging periods when there is a constant flux in the amount of charge coming from the panels as is likely to happen on a cloudy day.

Types of batteries

Before we delve into this sub-topic it is important to bear in mind a few things:

  1. The world of batteries is vast and constantly changing and this is not a journal article on the topic of batteries so we are going to breeze past the basics. Experts are free to chip in on the subject in the comment section.
  2.  It is unwise to use normal car batteries for your solar system, they are designed for quick discharge systems and are not suited for solar systems.
  3. Almost all types of batteries I know contain one dangerous chemical or another. You should not eat or drink when handling batteries and you should wash your hands with soap and water after handling them. Some batteries produce dangerous/flammable gasses and are not to be used indoors, in poorly ventilated areas or near naked flames.
  4. If you have watched action/spy movies you know batteries give a nasty shock. It probably won’t kill you but trust me you don’t want to be on the receiving end. To avoid risk of shock avoid handling both terminals at the same time.
  5. If you decide to be parsimonious when purchasing your batteries and end up buying a poor quality battery you will most likely end up regretting it. Always try to buy reputable brands of batteries. I am not going to recommend a single brand of batteries, there are too many. Just go the Gulf Complex or to suppliers of your choice and take note of the names of the batteries and go back home to research them first. Don’t just go with my guide!

There are many ways to classify batteries. I am going to ignore all these and tell you about the following types of batteries that you are likely going to encounter.

  • Liquid electrolyte (acid) batteries- these are the most common type of batteries. They usually require some form of maintenance such as battery water and acid topping or in some cases topping using a special concoction of the manufacturer’s choice. In the latter case make sure that this electrolyte is widely available. It wouldn’t do you much good to get stuck some months or years down the line if the supplier or manufacturer goes out of business and you have no way of getting the concoction. Make sure that the battery is a deep cycle battery. They are usually cheap costing around $1/AH
  • Maintenance free battery- these are also known as valve regulated lead acid batteries. These require significantly less attention compared to the normal lead acid batteries. They are usually sealed with non-removable caps. They still require cleaning though.
  • Gel batteries-a type of maintenance-free battery that uses a jelly-like electrolyte. They will cost you about $2-$2.50/AH at the Gulf Complex
  • Glass Mat batteries-sealed maintenance free batteries that do not produce emissions and are therefore ideal for home use. They will cost you about $2-$2.50/AH at the Gulf Complex.

The Ampere Hour

Just like with doctors and lawyers, the folks in the electricity business like to confuse us with their terminology. Battery capacity is usually measured in ampere-hours. If you remember an ampere measures the amount of electricity passing through a circuit.

1 Ampere-hour simply put means 1 amp for an hour. It means a 100 AH battery has a theoretical capacity to supply 1 amp for 100 hours ceteris paribus. Since we are assumed we will be building a 12 V system a 12 V  100AH battery produces 12 watts ( remember Power (P)=Current (I)XVoltage (V)) for 100 hours. In other words 1.2KWh! You can use the c

Since we are assumed we will be building a 12 V system a 12 V 100AH battery produces 12 watts ( remember Power (P)=Current (I)XVoltage (V)) for 100 hours. In other words 1.2KWh! You can use the calculator here to ease your calculations. Which would mean in Utopia one 100Ah battery would cover my needs which in part 2 we divined to be 1.24 KWh.

Alas! We do not live in Utopia, batteries in the real world hardly ever operate at a 100% and you should also never discharge your batteries completely. Not if you care for them or your pocket at all.

The general rule of thumb is to only discharge your batteries to about 50% that way they can last longer.  A discharge to 70% is even better. Then there are those cloudy days when your batteries won’t be fully charged. Taking into account the goulash of factors it would be a good idea (this is is not science) to triple your system requirements. Which means buying batteries with a 300Ah capacity.

Like with the panels, it is entirely up to you what type of battery or batteries you buy and the configurations you opt for. Three 100Ah batteries or as I did two 170Ah batteries.

Maintenance Free 100 Ah Lead Acid Battery$100
Maintenance Free 105 AH Battery$100
100 AH Gel Battery$200
170 AH Gel Battery$360
100 AH AGM Battery$200

We will touch battery configurations and wiring during the wiring installment, but it is important to note that you should only charge batteries using a regulator on your system or you risk damaging them. You should also constantly test your batteries and their performance to ensure that they are still working as intended.

The topic of batteries is long and winded and it is possible that I have omitted something important, or told a lie ( doubt that), if you have any questions, suggestions, tips please feel free to leave a comment.

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