If you’re interested in building a solar power off-grid energy system, then this is the most important article you’re ever going to read.
Here’s why:
By the end of this article you will know exactly how to pick out the best battery for your solar panel system.
In this article you will learn:
- Part 1: The difference between “deep cycle” and “shallow” cycle batteries and why you should avoid filling your battery bank with car batteries
- Part 2: The 3 main types of deep cycle solar batteries (lead acid, saltwater, and lithium)
- Part 3: A comparison of the components of batteries, such as: depth of discharge, capacity and power, efficiency, battery life, and manufacturer.
How Do Solar Batteries Work?
When you have a solar battery connected to your solar panel system,
excess solar energy can be stored in your batteries instead of going back
to the power grid
If your panels produce more electricity than you need, this energy can go
back to charging your batteries.
Then when it’s dark outside and your solar panels aren’t producing electricity, you can access that energy you stored in the daytime.
The electricity is sent back to the grid only when your battery is full or
draws from the grid only when the battery is low.
1. “Deep Cycle” vs “Shallow Cycle”: How Solar Batteries Differ From Car Batteries
Back when the renewable energy industry was just kicking off, people used car batteries to go “off the grid”.
This is less than ideal because car batteries are of the “shallow cycle” type.
What’s a cycle? Batteries go through the cycle of charging and then discharging.
You charge your battery up, and then discharge it by using it. That’s a cycle.
A shallow cycle battery is built to only give short bursts of energy and not be used for a very long time before returning to a fully charged state.
This is short, or “shallow” cycle, is why car batteries are meant to be used only for starting and ignition.
When you start your car, the shallow cycle car battery produces the sudden burst of power that you need to start.
They aren’t built to be continuously drained and discharged, which is what you want to do with the batteries in your home battery bank.
On the other hand, solar batteries are “deep cycle” batteries.
Deep cycle batteries are designed to handle the prolonged, repeated deep discharges that are needed in “off the grid” energy systems.
A deep cycle battery provides extended usage of the battery going well below 50% discharge before it is recharged again.
This is what you want.
The next thing you need to know is that there are three categories of “deep cycle” solar batteries that work best.
2. The 3 Main Types of Deep Cycle Solar Batteries
Now that you know that you’re dealing with a deep cycle solar battery, which one should you use?
There are three battery types that can work exceptionally well, and each has its pros and cons.
It all depends on what type of battery is a fit to your system, the battery quality you’re going for, and how much you are willing to spend.
We start with the “lead acid” battery.
Lead Acid Batteries
Lead acid batteries are the most popular rechargeable battery in the world.
They have been used for 150 years, and one of the most reliable batteries in existence.
Lead acid batteries are also the most common batteries in solar panel battery banks.
Compared to the other batteries in this list, lead acids are the cheapest…
but as a tradeoff, you get lower battery life and a smaller depth of discharge.
But if you aim to fill your battery bank with lots of batteries for a low cost, lead acid batteries are a great option!
Next we move on to “saltwater” batteries.
Saltwater Batteries
Saltwater batteries are more expensive than lead acid batteries, but they have a greater lifespan.
Unlike lead acid batteries which have been around for a long time, saltwater batteries are essentially brand new to the market and remain somewhat rare and untested.
Of the three types of batteries on this list, the saltwater battery has the greatest depth of discharge, meaning you’ll get the most output per charge before needing to recharge.
Lithium Batteries
Lithium batteries are the most expensive out of the three, but they are also the highest rated.
They are also the longest lasting out of the three, and have the second highest depth of discharge behind the saltwater battery.
An example of a lithium battery is the Tesla Powerwall.
Lithium vs. Saltwater vs. Lead Acid Compared
Cost
Lithium > Saltwater > Lead Acid
The cost of the lithium battery is the highest, followed by the saltwater, and then the lead acid.
While the old saying “you get what you pay for” holds true when buying batteries… in some instances certain batteries may be overkill for your system, so the most expensive battery may not always be the best choice.
Lifespan and Warranty
Lifespan: Lithium > Saltwater > Lead Acid
Comparing the lifespans, the lithium battery is greatest, followed by the saltwater, then the lead acid.
A battery’s lifespan declines after it’s ability to hold charge declines.
In most systems, a battery will cycle daily.
Meaning it will charge and drain regularly.
Then which each cycle, the battery’s ability to hold the same charge lessens.
With this in mind, a warranty that guarantees a certain number of cycles of life from a battery can be useful.
Or even better: You can extend the life of your batteries by using the maintenance and recondition methods the EZ Battery Reconditioning program teaches.
Depth of Discharge
Saltwater > Lithium > Lead Acid
Depth of discharge is how much you can drain the battery down before needing to recharge the battery without harming its life.
Certain solar batteries can be depleted further than others, allowing more use between charging.
Essentially, a battery with a 90% depth of discharge per cycle will provide more battery power per charge than a battery with less.