All batteries have a life span, so when we look at the options available for electrical storage, it’s important we consider what we want to do and as a result, how long it will be before we need to replace them.
Batteries
Lead Acid Batteries
Deep Cycle Lead Acid batteries were designed specifically for back up and off-grid solutions. In essence, they are very similar to your car battery, except that their lead plates are thicker. This means that they are able to use more energy from the battery than is required when you start your car.
Deep Cycle Lead Acid Batteries are a good budget option when looking for a start-up off grid energy storage system. However, it’s essential that you look after and manage them well in order to get the best life out of them.
They can vary from 250 – 2000 cycles, depending on the amount of lead that is used, and the depth to which they are cycled. A “cycle” in battery terms means going from fully charged to fully discharged and then charged back to 100%.
Consequently, Lead Acid Batteries last longer if you use the least possible amount of energy from them and reduce the cycle depth to between 20 – 30% of discharge.
It’s important to bear in mind that Lead Acid Batteries need to be fully charged on a regular basis, preferably at the end of each day. This helps prevent sulfation (small sulfate crystals), which drastically reduces the life of Lead Acid Batteries.
Lithium Ion Batteries
The price on Lithium Ion Batteries has dropped nicely in recent years. That said, it’s still more expensive per watt compared with Lead Acid Batteries. However, they can cycle of 10 000 times to 90% DOC (Depth of Charge) and do not need to be fully charged at any time.
The reason is that Lithium Batteries contain their own battery management system, which means that they cannot be overcharged or completely discharged.
The drop in the price of Lithium Ion Batteries, combined with the number of total cycles they can go through, as well as the fact that they don’t need to be fully charged all the time, makes them the best option for solar and off-grid solutions.
Here’s a basic costing comparison between Lead Acid and Lithium Ion Batteries:
Lead Acid Batteries: 5KW costs about R8 000 @ 1 000 cycles @ 50% DOD (2.5KWh) – cost per KWh used = R3.20
Lithium Ion Batteries: 5KW costs about R50 000 @ 10 000 cycles @ 90% DOD (4.5 KWh) – cost per KWh = R0.93
As you can see, the cost of Lithium Ion Batteries is far more cost effective in the long run, when you compare the per cycle cost.
The other major advantage of Lithium Ion Batteries is that based on the fact that they give you 10 000 cycles, your battery should last up to 27 years.