Modern solar batteries last around 15 years with decent usage conditions, which is impressive when you consider that just about a decade ago, many systems had messy lead-acid batteries with a 4-year lifespan.
Like most other electrical devices, how you use your battery affects its lifespan. However, a modern lithium-ion battery can last around 10 or more years even in the most demanding conditions. Let’s take a closer look at how and why batteries approach their end of life. Plus, we’ll also go over what you can do to slow down your battery’s ageing, which is thankfully easier than slowing down our own ageing.
Factors Affecting the Lifespan of a Solar Battery
Batteries are simple things — the more you put them to use, the faster they degrade. The worse their operating conditions, the shorter they last. Let’s understand this better:
Number of cycles
A battery will approach its end of life faster if you subject it to more charging and discharging cycles, just as a car with more kilometres will degrade faster than one with a low odometer reading. With each charging and discharging cycle, the battery’s capacity drops slightly. While the capacity decrease is not noticeable over a single cycle, the tiny difference adds up over the years. This is the main reason why manufacturer warranties are also linked to the number of cycles (again, just as a car warranty is linked to both years and kilometres).
Environmental conditions
Just like us, batteries exhaust faster in hot, humid conditions. A solar battery will perform best in 20-25 degrees Celsius, and consistently operating it in hot conditions will reduce its lifespan significantly.
State of Charge
Although it feels oddly satisfying to see a ‘100% charged’ status on your battery, regularly charging it to its maximum capacity can adversely affect its capacity. The technical term for this effect is ‘trickle charging’, wherein the battery is charged from 90% to 100% capacity. These last few percent of charge can elevate the battery’s temperature and affect its lifespan and performance. Oh, and here’s a pro tip: this applies to your smartphone batteries as well, since they use the same chemistry as your solar battery.
Depth of Discharge
A battery’s depth of discharge is the measure of how much of its stored energy you can extract. Modern lithium batteries are superior to older technologies as they have a much higher depth of discharge, often touching the 100% mark. However, draining a battery to a 0% charge takes a toll on its capacity. Again, batteries are like us in this sense — if someone works till they faint and fall each day, they’re probably not going to have a long and healthy life. Here’s a graph by Saft, a leading battery maker, showing the correlation between depth of discharge and available number of cycles, AKA lifespan.
Note that a battery that’s only discharged by 30% in each cycle will last over four times longer compared to a battery that’s fully discharged in each cycle.
Overcharging
If you ever had one of those seemingly indestructible Nokia mobile phones, you know that charging them overnight was a bad idea, as the battery then swelled like it was stung by bees. While your solar battery won’t change shape from overcharging, its performance and capacity will definitely be affected if you regularly overcharge it.
Battery Warranty: The Minimum Lifespan
A great way to predict the lifespan of a solar battery, or anything for that matter, is to look at its warranty. Most reputable battery brands today offer a 10-year product warranty. Needless to say, manufacturers are generally conservative when setting a warranty period. This means you can expect your battery to last well beyond the warranty duration. Most experts will tell you that with the ideal usage conditions and care, batteries can last up to 20 years.
Here’s a snapshot from the warranty document for the Tesla Powerwall, a popular battery choice:
How to Tell if a Solar Battery is Nearing its End of Life?
End-of-life can mean different things to different people. But with solar batteries, end of life can be defined as a point when the battery capacity and performance drop so drastically that it barely serves its purpose. Here are a few signs that your battery is starting to say goodbye!
Decreased Capacity
The most obvious and most common indicator that a battery’s life is coming to an end is a significant decrease in its storage capacity. For grid-tied batteries, reduced capacity may not require discarding your battery if you only need it for a few minutes of backup every now and then. For off-grid systems, however, severely decreased capacity may mean game over as the battery is likely the only thing providing you with solar energy at night.
Malfunctioning
If your solar battery is well beyond its warranty period and regularly malfunctions, it may be a sign that it is trying to quit. For instance, if a battery shuts down abruptly, particularly during high demand, it may be time for it to go to the recycling centre.
BMS Alerts
A battery’s BMS (battery management system) monitors all of its functions and alerts you if something seems wrong. If your battery is nearing its life’s end, it probably won’t perform properly, resulting in frequent BMS alerts.
Overheating
Overheating is a common indicator of significant degradation in any electrical or electronic device, and this applies to solar batteries too. Each battery has a cooling system, either using a fan or a cooling liquid. Older batteries will heat up faster, and their cooling systems will be less effective.
Ways to Prolong Your Solar Battery’s Life
As you’ll have gathered from one of the previous sections, the best way to maximize your battery’s lifespan is to avoid all the things that accelerate its ageing. Here’s a quick summary:
Don’t Overcharge
As mentioned earlier, overcharging can lead to decreased capacity and shortened life. Thankfully, most modern batteries have a smart BMS (battery management system), which keeps checking the state of charge and shuts off power flow when it is fully charged.
Nevertheless, if you have an off-grid system that can’t export excess solar power, you may want to use a “dump load” such as a water heater to divert the solar energy from the battery and prevent your battery from overcharging.
Don’t Fully Drain Your Battery
Even if your battery has a depth of discharge of over 90%, it is best not to regularly test it. The best way to do this is to size your battery in a way that it has more capacity than your daily needs. Also, if you expect an outage that may drain your battery fully, plan in advance and use minimal energy so that your battery isn’t at zero charge when the grid power is back. You can also make alternative arrangements, such as a petrol or diesel generator, to aid your solar battery during blackouts.
Install In a Cool Place
Solar batteries generate enough heat on their own, and keeping them in a hot area will mean even more heating, severely affecting their lifespan. Most manufacturers recommend installing your battery in a shaded, cool place such as a garage.
Summing It Up
Once considered an expensive and optional upgrade, solar batteries are now becoming a default choice with solar power systems. The Solar Energy Association of New Zealand (SEANZ) estimates that 30% of all solar power systems installed in the country over the last years have lithium-ion batteries. The Ministry of Business, Innovation and Employment (MBIE) considers that in a ‘disruptive scenario’, we can expect every solar power system to include a solar battery by 2030.
With such a rapid rise in the adoption of solar batteries, their lifespan becomes an important factor for consideration. Thankfully, solar batteries are now smarter, more compact, and much more long-lasting than their ancestors. Most solar batteries come with a 10-year warranty, and can last almost twice that duration if used properly.
Lastly, different batteries offer different features and specs, and if you are looking to install a new solar battery, we recommend comparing different models before making a choice. It is also a good idea to get multiple battery quotes and choose an installer that suits your needs best.
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