The short answer: Expect a home battery in a temperate climate with typical use to last 15 – 17 years. Solar batteries exposed to higher temperatures, and worked hard every day, could have an effective life of 12 – 14 years.
The longer answer:
Treat your solar battery with the care you’d give to a newborn in nappies, and it’ll still be powering when the kid asks you to borrow the car keys. Neglect it, and the lights might be out before that child finishes primary school.
Unlike your children though, your home battery comes with a guidebook to secure its longevity. With that guidebook and the help of some scientific research with hands-on experience, this article will attempt to provide some insights to extend your battery’s lifespan, which won’t be anywhere near as demanding as your firstborn.
Defining End-Of-Life For A Solar Battery
Off-Grid
In off-grid solar battery systems, the concept of ‘end-of-life’ is better defined compared to grid-tied systems. In off-grid setups, the battery serves as the primary energy source, and there will come a point where its capacity and performance have degraded to a level where it can no longer support the load. Then it’s lights out.
Grid-Tied
For grid-tied systems with backup capabilities, the definition of end-of-life is less straightforward, as the battery can still be useful for backup purposes even if its capacity has significantly degraded, as long as it can meet the essential backup load requirements during power outages.
If the main function of a grid-tied battery system is for peak demand management to reduce electricity bills, it can be even more challenging to precisely determine the end of life. Unlike an off-grid system, the grid invisibly steps in to provide power when needed.
Manufacturer’s Warranty Period
The end of the manufacturer’s warranty period, typically 10 years1, and/or exceeding the warranted number of cycles, is often considered the end-of-life when justifying a solar battery’s economics.
However, in reality, the lifespan might be longer if treated well, because manufacturers typically design their warranties with a degree of conservatism. The SoH (State of Health) designated under the warranty is set to ensure a reasonable level of battery performance, as long as it’s operated within the manufacturer’s specifications.
GOODWE Limited Warranty for Lynx Series LX F Battery System shows a 10-year product and performance warranty of 70% useable energy and a minimum throughput based on battery size. Image: GoodWe
What Are The Symptoms Of A Degraded Solar Battery?
The symptoms can vary depending on chemistry, design, and usage. Here are some common signs that might indicate an end-of-life battery in a home solar storage system:
Reduced Capacity: One of the primary indicators of an aging solar battery is reduced capacity. You may notice that it holds less energy than it used to, leading to shorter discharge times.
Frequent Recharging: As the battery’s capacity decreases, it may require more frequent recharging to maintain the same level of performance. You might find yourself needing to charge it more often than before.
Decreased Performance: The battery’s ability to deliver power might diminish. This would become more conspicuous when the system is in backup mode or in an off-grid configuration.
Increased Heating: Ageing batteries can experience increased internal resistance, generating more heat during charging and discharging. If you notice it becoming unusually hot during normal operations, it could be a sign of degradation.
Unexpected Shutdowns: An end-of-life battery might experience unexpected shutdowns or interruptions in power delivery, particularly noticeable during periods of high demand when it struggles to provide the required energy.
BMS Warnings: Many modern systems have a Battery Management System (BMS) that monitors the battery’s health. If the BMS consistently alerts you to issues, it could be a sign that it is reaching the end of its useful life.
Factors That Affect The Lifespan Of A Battery: The Big Three
#1 Temperature Extremes
Like you and me, a battery works more efficiently when not subjected to extreme temperatures. The sweet spot is similar to ours, too – around 20 to 25ºC. The large temperature variations in many parts of Australia don’t do solar batteries any favours, so expect them to last longer in temperate zones or temperature-controlled environments.
Exposure to temperatures above the recommended range accelerates chemical reactions within the battery, leading to faster degradation of its components. High temperatures also cause capacity to decline rapidly, resulting in a shorter usable lifespan.
Frequent exposure to extreme cold can also decrease a battery’s efficiency and contribute to long-term degradation of its capacity and overall lifespan. Severe cold can even lead to mechanical stress on the battery, potentially impacting its structural integrity.
Optimal operating temperature zones and characteristics for lithium-ion batteries. Image: Researchgate
#2 Number Of Charge/Discharge Cycles
It’s not by accident that many manufacturer’s warranties are linked to the number of charge/discharge cycles in a solar battery’s life. Each cycle contributes to gradual wear and chemical changes, leading to capacity degradation over time.
Lead-acid energy storage is more affected by the number of cycles than lithium-ion batteries. Frequent cycling, especially deep discharges, can contribute to sulphate buildup on the battery plates, which reduces capacity and shortens its lifespan.
Lithium-ion batteries can tolerate a higher number of cycles and deeper discharges. Minimizing the frequency of cycles through efficient energy management can help extend the its longevity, no matter the chemistry.
#3 Depth Of Discharge (DoD) And State Of Charge (SOC)
The Depth of Discharge (DoD) is the degree to which a battery is emptied relative to its total capacity. A large DoD significantly impacts lifespan of a battery by affecting the amount of stress placed on its chemistry. Shallower discharges, where it is not fully drained, lead to slower capacity degradation and extended overall battery life.
A manufacturer’s battery warranty often includes stipulations related to the DoD. For example, a manufacturer might specify that a lithium-ion battery should not be regularly discharged beyond a certain percentage of its capacity (e.g., 80% DoD) to maintain warranty coverage. Exceeding these recommended DoD levels can lead to accelerated degradation that some warranties may not cover.
State Of Charge (SoC), on the other hand, indicates the current charge level of a battery as a percentage of its maximum capacity. Manufacturers of Li-ion batteries may recommend avoiding consistently charging it to 100% SoC. While these SoC limits might not be as prominently mentioned as DoD limits, adhering to appropriate SoC levels can help preserve the solar battery’s capacity and lifespan.
Regression curve of Lithium-ion battery cycle life vs DOD. The graph indicates that a shallower discharge will extend the cycle life. Image: Researchgate
Empirical Studies To Determine Solar Battery Lifespan
Empirical research involves collecting data through observation and experimentation to draw conclusions, rather than theoretical analysis. Many such studies have been undertaken in recent years aiming to determine the likely lifespans of batteries.
One study in particular, titled ‘Lifetime Expectancy of Li-Ion Batteries Used for Residential Solar Storage‘, aimed to give a definitive answer to what seems like a rhetorical question. Researchers engaged in hands-on experimentation with 24 lithium-ion batteries, simulating real-world conditions to determine their lifespan. This is what they did:
Temperature Effects: Solar batteries were exposed to a range of temperatures to emulate the various climatic conditions they may be installed in. The study noted those exposed to higher temperatures aged more rapidly, indicating that you might see a bit faster wear in the northern regions of Australia than down south.
Charge/Discharge Cycling: By simulating the daily load profiles of average households, researchers could track the battery charge/discharge cycles to see how it affected them over time. As expected, those that were put through more frequent charge/discharge cycles showed signs of quicker degradation.
Depth of Discharge Impacts: Batteries were subjected to various depths of discharge. Some were shallow cycled, while others were almost entirely drained. No surprises – those subjected to a deeper depth of discharge before recharging degraded faster than those that weren’t.
Degradation evolution throughout 10 years under warranty conditions for two commercial Li-ion battery packs analyzed in the study. Image: MDPI
How Did The Numbers Stack Up?
The outcome of this study suggested you could expect your solar battery to last beyond its 10-year warranty. Researchers found that batteries kept in temperate climates and had average use could last between 15 to 17 years. On the other hand, those exposed to higher temperatures we might see in the hotter regions, and pushed hard every day, could have an effective life of 12 to 14 years.
Bear in mind this is only one such study. In another testing facility, solar batteries haven’t fared so well. The recently closed Canberra Battery Test Centre published a report in which the outcome of 26 batteries tested over 6 years was found wanting. After a good hammering, only 2 out of the 26 were fault-free, although no numbers were given for estimated lifespans.
Testing Times And Insights To Prolong Battery Life
Regardless of any outcomes from studies undertaken, there’s no argument that the lifespan of a solar battery hinges upon just a few key factors – reducing temperature extremes, managing the charge/discharge cycles, and minimizing the depth of discharge being the main ones.
I’m confident that you won’t have to nurture your battery like a baby, and with some common sense, it will happily outlast the 10-year warranty period.
Footnotes
- Props to Enphase & Q-Cells, which warrant their batteries for 15 years, and Zenaji, which offer a 20-year warranty – albeit with lots of carve-outs for temperature exposure. ↩
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