The following is a Depth of Discharge chart for all batteries. If you have ever carried out research before going solar, one of the things that you will have heard is that batteries, in general, should only be discharged to a safe depth of discharge. If, as an example, you get a battery that has 100ah, it doesn’t mean that you are going to be able to safely use up all the power to a depth of 100%. Indeed, you are going to be using up way less than this. DOD is something that you need to be cognizant of when setting up your home solar system. *Note that the information given here is general and not meant to replace information coming from your battery’s manufacturer.
|Type of Battery||Depth of Discharge||Remaining capacity|
|Flooded lead acid batteries||50%||50%|
Type of Battery with Best Depth of Discharge
As you can see in the above depth of discharge chart, lithium batteries are much better at being discharged than all the other types of battery. In fact, you can discharge an lithium battery to a depth of 90% and you will get the same lifespan as a flooded lead acid battery that’s being discharged to a depth of 50%.
Lithium batteries are followed by AGM batteries in terms of Depth of discharge, as you can see in the above chart.
What is Depth of Discharge?
The term Depth of Discharge refers to the amount of energy that has been removed from a battery in relation to its total capacity. Thus if you have used up half of the capacity in a battery, then the DOD is 50%.
Let’s use the example of a solar battery that has a capacity of 200ah. What that means is that when it is fully charged, the battery will have 200ahs. Now, if we use up the battery till we are left with 80ah total, it means we will have discharged it to a capacity of 20%. If continue using the battery till we have a capacity of 10ah, then out DoD will be at 90%.
Where does DOD apply?
The issue of depth of discharge does not only apply to solar batteries. Automotive batteries are even more sensitive when it comes to the level to which they can safely be discharged. So, what is meant by depth of discharge in batteries and how does it affect your off-grid solar system?
Why it’s important to understand the DoD in batteries.
The Depth of Discharge is something that you should be painfully aware of when setting up your home solar system. That’s because, as already mentioned, batteries are not designed to be discharged to a depth of 100%. Trying to do this is a good recipe for killing your battery. Indeed, it is safer to use up as little power as is possible in a battery as a way of extending it’s life. Now, not using our systems would hardly be practical. There, are, however, certain guidelines that need to be followed when it comes to depths of discharge in solar batteries;
As you can see, Gel batteries have a better DoD than other lead acid batteries. That means you can get away with using a lot more of their capacity. However, as a general rule of thumb, you should set up your system in such a way that each batteries is drained to as shallow a DoD as is possible. That way, you will get many more cycles of life from it. Of course, the DoDs that are given above are only estimates. If you need a correct figure, you should check out with the manufacturer.
Looking for the best type of battery for your home solar system? Then you need to read the provided article. Also take note that you should NEVER buy used solar batteries. Otherwise your entire project will come to grief.