Batteries are a key component in all our off grid solar kits. They are also your biggest investment, so it is very important to look after them to maximise their lifespan!
Batteries degrade with use - whether it’s your phone or car or solar battery, it’s unavoidable. The more times they are charged and discharged, the lower the capacity becomes, and eventually they will have too little capacity to meet your needs, so you will need to replace them. However, the way you use them can have a significant impact on how much life you can get out of them.
This article will cover the causes of premature degradation, and preventative methods, so you can get the most out of your batteries.
We offer two types of solar batteries here at GridFree, Gel (aka sealed lead acid) and Lithium (aka LiFePO4). The Gel batteries have an expected lifespan of 3-5 years with daily use, and Lithium about 10-15. Both batteries are considered maintenance-free, but if you want to maximise their lifespan, there’s a couple things you need to be aware of when using them.
The same treatment will affect the two batteries differently, so different care is need for each, and we'll cover both in this article.
This is when you discharge your batteries too much, shortening their cycle life. The threshold of ‘too low’ for Gel is about 50% of their full capacity and for lithium this is about 80%.
These recommendations come from the manufacturer and are designed to give you the best balance of lifespan and usage.
For example, if you were to discharge a gel battery to 50% you’re expected to get about 1500 cycles. If you discharged down to 25% you might get 25% more energy per cycle, but you would only be expected to get around 700 cycles out of the battery. Practically that could cut your battery’s lifespan in half.
So how do I prevent over-discharging?
The most effective way is to keep a close eye on how much power you're using, and slow down or stop as you start getting close to too low, as well as paying attention to the weather forecast to know if you're likely to have an extended time with less sun. This was you can prepare for times when your batteries won't be getting extra charge and you may need to cut back so that you won't use too much power because you can't switch off something important. Having a generator available will also be a big help for these times.
A system cut-off is also a great safety measure to prevent human error.
For Gel batteries you need to set your inverter to stop outputting power when your batteries get to 50%. In an ideal world, you simply set the correct voltage cutoff corresponding to 50% of your battery bank’s capacity:
However, battery voltage is not the only thing that predicts state of charge. The rate of discharge (i.e. how much power you’re drawing) also affects the voltage.
What this means is that if you are drawing a lot of power, your batteries will hit that voltage number before they are at 50% charge. This isn’t necessarily a bad thing; it just means if you use these voltages as your cut off, you are being more cautious. So, you might choose to set your cut off differently if necessary.
When it comes to Lithium batteries, over-discharging does not have the same impact as on Gel, nor do they require the same user input. The inverter will shut them off at 20% by default, and the battery itself has built in safety cut offs at 10%. These batteries will also give you an accurate percentage of charge - like your phone – so you don't have worry about interpreting the voltage.
Leaving your batteries partially charged
This is where your batteries are sitting at less than 100% for a sustained period, whether that's being partially recharged or untouched. This can cause rapid sulfation – a buildup of lead sulfate crystals covering the battery plates. This coverage deteriorates the overall efficiency and power storage capability of the battery, meaning over-discharging and inadequate recharging will result in a loss of battery capacity.
If you regularly leave your batteries at a partial state of charge this damage will add up over time, and if you leave them very low, it will only take a couple days for damage to occur.
The lithium batteries are far more tolerant to this but still will be affected if you leave them very low for several months.
How do I prevent this?
The first and best preventative measure is to make sure your kit is adequately sized - having the right balance of power generation, storage, and usage. If it is, you will charge your batteries to full virtually every day so there will be nothing to worry about. For more information about sizing your kit, read this article.
If you already have a kit and you are finding that you cannot get your batteries to full most days, then you need upgrade the system, add in a back-up generator, or see what you can do to cut back on power usage. You can read more about expanding an existing kit here.
If your batteries will be stored for an extended period of time (such as before installation) you should make sure you store them at full charge for the gel, and about 75% charged for lithium. The Gel should be recharged every 3 months or so, and the lithium every 6.
All equipment has operating environment requirements, and batteries are no different.
Both batteries should not be below 0 degrees Celsius at any point because there is a possibility that they can freeze. This is especially important for the lithium batteries, as operating them near or below this temperature will cause them to lose lifespan rapidly.
You also do not want to operate these in conditions too hot. Batteries actually have an increased capacity over certain temperatures however they will lose lifespan rapidly when used at that temperature.
For Gel, the operating temperature range is 15-35 degrees Celsius, and Lithium is 0-45 degrees Celsius.
This is where individual batteries are discharged by different amounts, so they are always sitting at different charge levels. This is bad for all batteries involved as the worst one drags the others down, and usually only gets worse if not corrected. This is only an issue for gel batteries, as the lithium systems communicate between themselves.
An imbalance is usually caused by one of two things: using batteries of different ages in the same battery bank, or running loads off only some of the batteries in the bank.
How do I prevent this?
If you need to expand your battery bank, we recommend adding new batteries within 6 months of purchase to prevent imbalances due to age.
Running a DC load such as 12V lights from only one battery will age that battery faster than the rest. If you want to run 12V loads, you need to get a DC-DC converter that draws power from your entire battery bank and steps it down to 12V. This ensures that the stress of use is shared equally among the batteries, and they will age at the same rate.
This is where you draw too much power for a sustained period, or just way too much in an instant by shorting your batteries out.
Shorting is usually caused by crossing the leads or dropping a metal tool across two battery terminals – you'll know when this happens because you will hear a pop and see a spark. It’s important to be careful when working around the batteries, as even a second of being short-circuited can often greatly damage a battery.
The sustained case of overcurrent damage occurs when discharging the battery faster than its recommended discharge rate. For example running a high wattage appliance from a small battery bank for a sustained period of time.
Our kits are designed to help prevent this kind of damage, and it's not something you're likely to encounter with normal usage - however if you have any doubts about whether an appliance you want to use might be an issue, we're happy to let you know.
If you have any questions about battery care, or off grid solar in general, please get in touch!