How Long Does a Solar Battery Last?

Solar batteries are becoming more popular ' and beneficial ' as utility providers adopt time-of-use rates, grid outages increase, and homeowners increase their appetite for clean energy.

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But as a new technology, there are a number of questions surrounding home battery storage. One of the bigger questions is how long solar batteries will last before they need to be replaced. After all, it's only natural (and wise) to want a sense of how long your multi-thousand-dollar battery investment is going to last.

In this article, we'll explore:

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How many years does a solar battery last?

The lithium-ion solar batteries being made today have an expected operational lifespan of 10 to 15 years, depending on the model, chemistry, usage, and the average temperature of the unit.

However, home battery storage doesn't simply shut down after a certain length of time. Like solar panels, battery performance naturally degrades over time until it reaches a point where it is no longer useful or recommended to continue operating. For example, modern solar battery warranties typically guarantee 70% of nameplate capacity after 10-12 years or a certain number of cycles or throughput. That means a 10 kWh battery should still have 7 kWh of usable capacity when the warranty expires ' which is still a substantial amount of storage, but not quite the 10 kWh you originally decided upon.

Historically, manufacturer's warranties tend to be on the conservative side, so it's plausible that today's solar batteries will last longer than expected (as EV batteries have been), but we simply won't know until real-world results roll in over the next 10-15 years.

Factors Impacting Solar Battery Lifespan

There are five main factors that influence the lifespan of a lithium-ion solar battery. These are:

• Battery type
• Usage
• Ambient temperature
• Manufacturer/model of the battery
• Maintenance

Let's take a closer look at each factor.

Battery Type

Perhaps the biggest factor in determining the lifespan of a solar battery is its chemical composition. For example, the lithium-ion batteries that make up a majority of today's residential solar battery market have an expected operational lifespan of 10-15 years, while the lead-acid batteries that dominated the market in previous decades were expected to last around 5 years.

Looking ahead, emerging flow battery technologies that have yet to hit the residential market may have lifespans of up to 30 years.

Battery type Cycles before degradation Operational lifespan Lithium-ion (non-LFP) 500 to 1,000 10+ years Lithium iron phosphate (LFP) 1,000 to 10,000 10-15 Lead-acid 500 to 1,000 ~5 years

Since lithium-ion batteries dominate today's market, let's take a closer look at how long they last.

Related reading: Types of Solar Batteries A Comprehensive Guide

How long do lithium batteries last?

In general, lithium-ion solar batteries have an expected operational lifespan of 10-15 years. However, there are lifespan differences within the greater category of 'lithium-ion' batteries.

For example, a National Renewable Energy Laboratory (NREL) study published in Applied Energy found that the lifespan of lithium iron phosphate (LFP) batteries is less affected by high temperature and depth of discharge (how far you drain the battery's capacity at one time) than lithium nickel manganese cobalt oxide (NMC) batteries. Meanwhile, the lifespan of NMC batteries is less impacted by a high average state of charge (keeping your battery fully charged for prolonged periods of time) than LFP batteries.

All of that is to say that the type of battery you choose ' even within the category of lithium-ion ' has a substantial impact on how long it will last.

 

 

Battery Usage

Another major factor in battery lifespan is how you use it. This includes how often you charge and discharge your battery, the depth of discharge, and the average state of charge.

There are three basic battery usage modes ' self-consumption, time-of-use, and backup ' each with a unique impact on battery life. The table below provides a summary of each mode and its impact on battery life.

Battery mode Features Impact on NMC lifespan Impact on LFP lifespan Self-consumption

• Deep & frequent discharge cycles
• Low average state of discharge

Substantial capacity degradation, especially in smaller batteries Minimal capacity degradation Time-of-use

• Deep & frequent discharge cycles
• High average state of charge

Severe capacity degradation, especially in smaller batteries Moderate capacity degradation Backup

• Infrequent charge and discharge cycles
• High average state of charge

Minimal capacity degradation Moderate capacity degradation

Self-consumption mode

Self-consumption mode is when battery storage is used exclusively to store power from a home solar system and discharge it to power the home itself, with the goal of avoiding interaction with the grid altogether. The battery starts the day with a minimum charge, charges to 100% using excess solar generation throughout the day, and then discharges as much as possible during the evening and night.

Given the frequent and deep discharge cycles, self-consumption mode can substantially reduce the lifespan of an NMC lithium-ion battery but has minimal effect on the lifespan of LFP batteries that tolerate greater depth of discharge (often 100%).

Time-of-use (TOU) mode

Time-of-use mode is similar to self-consumption mode, however, instead of leaving the battery at a low state of charge overnight, the battery is charged using grid electricity during off-peak rate periods and therefore maintains a high average state of charge.

According to the NREL analysis of residential batteries, the high average state of charge in time-of-use mode contributes to faster degradation and shorter lifespans, especially in small NMC batteries.

Backup mode

In backup mode, the battery's primary purpose is to power essential systems when the grid goes down. As such, batteries in backup mode remain at a relatively high average state of charge, perform infrequent charge and discharge cycles, and enjoy longer lifespans than batteries in self-consumption and time-of-use modes.

According to the NREL study, NMC lithium-ion batteries fare especially well in backup mode given their tolerance to maintaining a high state of charge.

To recap, how you use your solar battery is a major factor in how long it lasts. Connect with an Energy Advisor to discuss the best battery option for your goals.

Battery Temperature

Environmental conditions ' specifically temperature ' play a crucial role in determining how long a solar battery will last. The NREL studied the effect of ambient temperature on residential solar batteries in and found:

'In all the simulation cases ' a lower cell temperature improves battery life to varying degrees, whereas a higher temperature degrades the cell much faster. For example, the lower Minneapolis temperature allows the (smaller nickel manganese cobalt oxide battery) to operate for more than 10 years before reaching 80% of its initial capacity.'

Image via NREL.

Key takeaways regarding temperature and solar battery life:

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• High ambient temperatures (Phoenix) can have a substantial impact on battery life, especially for NMC lithium-ion batteries
• LFP batteries withstand cold temperatures (Minneapolis) better than NMC lithium-ion batteries
• NMC batteries, time-of-use mode, and high temperatures are a recipe for a short battery life

Manufacturer, model, and warranty

Another factor in battery life is its manufacturer and model, although this generally has less influence than chemistry, usage, and temperature.

As with most products, you get what you pay for with solar batteries. Name-brand batteries tend to cost a bit more upfront but make up for it with longer lifespans and stronger warranties. The same concept applies to installation. An experienced and certified battery installer may charge a bit more, but a properly installed solar battery will last much longer than a poorly installed one.

The model or generation of the battery also makes a difference (much like the battery life of iPhones improving with each new model).

For example, Enphase offers a 10-year warranty on its second-generation IQ 3's and 10's and a 15-year warranty on its third-generation IQ 5P. So, in a matter of one generation and a few years, Enphase felt comfortable increasing its warranty length by 5 years and 2,000 cycles.

Solar battery warranties

And that brings us to the next indicator of solar battery life: Manufacturer warranties. Battery warranties guarantee a certain level of usable capacity after a specific time period, number of cycles, or total energy throughput.

While these are not hard-and-fast indicators of battery life, they provide hints as to which batteries are expected to last the longest.

Warranty terms for popular solar batteries

Make/Model Initial usable capacity Warranty Franklin Home Power 13.6 kWh 70% capacity after 12 years or 43MWh throughput LG ESS Home 8 14.4 kWh 70% capacity after 10 years or 59.8 MWh throughput sonnenCore+ 8.6 kWh 70% capacity after 10 years or 10,000 cycles LG RESU 10H PRIME 9.6 kWh 70% capacity after 10 years or 32MWh throughput Enphase IQ Battery 3/10 3.36kWh / 10.08 kWh 70% capacity after 10 years or 4,000 cycles Enphase IQ 5P 5 kWh 60% capacity after 15 years or 6,000 cycles Tesla Powerwall 2 13.5 kWh 70% capacity after 10 years (unlimited cycles) SunPower SunVault 13 kWh / 19.5 kWh 70% capacity after 10 years (unlimited cycles)

Of course, it's always a good idea to read the entire warranty agreement so you know exactly what is covered. For example, Tesla offers an unlimited cycle warranty on its Powerwall 2, however, the warranty states:

'If you only use your Powerwall for self-consumption of solar energy generated by an onsite array and for storing that solar energy for use as backup power, there is no limit on the number of times that you can cycle your battery in this ten year period.'

This seems to imply that charging a Powerwall 2 from the grid in time-of-use mode (which the NREL found to substantially decrease capacity in NMC batteries like the Powerwall) is not covered by the unlimited cycles warranty ' which is important to know before you finalize your battery purchase.

Solar Battery Maintenance

Lithium-ion solar batteries famously require very little maintenance. In fact, there's virtually no hands-on maintenance required unless you notice an issue with the battery's appearance or performance, in which case all repairs should be done by a trained and certified technician.

However, as a homeowner, you can contribute to a long battery life by keeping an eye on your battery's health.

• Monitor your battery's state of charge (SOC) and depth of discharge (DOD) to ensure they are within the manufacturer's recommendations
• Monitor charge and discharge performance to ensure the battery is working as intended
• Maintain a cool, dry, and unclutter environment around your battery

The sooner you can identify and correct battery issues, the longer your battery will last.

 

 

Maximizing Solar Battery Lifespan

There are a few ways to extend the life of your solar battery, most of which take place before the battery is even installed.

First, choose the right size and type of battery for your intended use. For example, the NREL found that LFP batteries maintain capacity longer in self-consumption and time-of-use modes, while NMC lithium-ion batteries maintain capacity longer in backup mode.

The NREL also found that 'battery life can be extended by oversizing the battery and cycling it within a narrower (state of charge) window.' So, a 10 kWh battery that regularly discharges 60% can be expected to last longer than a 6 kWh battery that regularly discharges 100%.

Next, site your battery in a temperature-controlled environment. Extreme heat and cold (but especially heat) can substantially impact battery life. At a minimum, have your battery installed out of direct sunlight if you live in a warmer climate.

Third, adhere to manufacturer recommendations for depth of discharge. If your manufacturer lists a 90% maximum depth of discharge, then always keep your battery charged to at least 10% capacity.

Finally, regularly monitor your battery's performance. Most lithium-ion batteries are Wi-Fi enabled and come with mobile apps to monitor performance. Get comfortable with this software and your battery's typical performance so you can quickly identify and correct issues.

When do you need to replace a solar battery?

With solar panels warrantied for 25-30 years and batteries warrantied for 10-15, there will likely come a time when you need to supplement or replace your battery storage.

Exactly when this day comes depends on your energy needs and the factors described above. However, one thing is certain: When it's time to supplement your energy storage in 10-15 years, solar batteries will be a fraction of the price they are today. And the more you maximize the lifespan of your current battery, the less money your next battery will cost.

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