In Parts 1 and 2 of this series, pv magazine reviewed the productive lifespan of residential solar panels and inverters. Here, we examine home batteries, how well they perform over time, and how long they last.
Residential energy storage has become an increasingly popular feature of home solar. A recent SunPower survey of more than 1,500 households found that about 40% of Americans worry about power outages on a regular basis. Of the survey respondents actively considering solar for their homes, 70% said they planned to include a battery energy storage system.
Besides providing backup power during outages, many batteries are integrated with technology that allows for intelligent scheduling of the import and export of energy. The goal is to maximize the value of the home’s solar system. And, some batteries are optimized to integrate an electric vehicle charger.
The report noted a steep uptick to consumers showing interest in storage in order to self-supply solar generation, suggesting that lowered net metering rates are discouraging export of local, clean electricity. Nearly 40% of consumers reported self-supply as a reason for getting a storage quote, up from less than 20% in 2022. Backup power for outages and savings on utility rates were also listed as top reasons for including energy storage in a quote.
Attachment rates of batteries in residential solar projects have climbed steadily in 2020 8.1% of residential solar systems attached batteries, according to Lawrence Berkeley National Laboratory, and in 2022 that rate climbed over 17%.
Life of a battery
Warranty periods can offer a look in installer and manufacturer expectations of the life of a battery. Common warranty periods are typically around 10 years. The warranty for the Enphase IQ Battery, for instance, ends at 10 years or 7,300 cycles, whatever occurs first.
Solar installer Sunrun said batteries can last anywhere between 5-15 years. That means a replacement likely will be needed during the 20-30 year life of a solar system.
Battery life expectancy is mostly driven by usage cycles. As demonstrated by the LG and Tesla product warranties, thresholds of 60% or 70% capacity are warranted through a certain number of charge cycles.
Image: LG Chem
Two use-scenarios drive this degradation: over charge and trickle charge, said the Faraday Institute. Overcharge is the act of pushing current into a battery that is fully charged. Doing this can cause it to overheat, or even potentially catch fire.
Trickle charge involves a process in which the battery is continually charged up to 100%, and inevitably losses take place. The bounce between 100% and just under 100% can elevate internal temperatures, diminishing capacity and lifetime.
Another cause of degradation over time is the loss of mobile lithium-ions in the battery, said Faraday. Side reactions in the battery can trap free usable lithium, thereby lowering capacity gradually.
While cold temperatures can halt a lithium-ion battery from performing, they do not actually degrade the battery or shorten its effective life. Overall battery lifetime is, however, diminished at high temperatures, said Faraday. This is because the electrolyte that sits between the electrodes breaks down at elevated temperatures, causing the battery to lose its capacity for Li-ion shuttling. This can reduce the number of Li-ions the electrode can accept into its structure, depleting the lithium-ion battery capacity.
Maintenance
It is recommended by the National Renewable Energy Laboratory (NREL) to install a battery in a cool, dry place, preferably a garage, where the impact of a fire (a small, but non-zero threat) may be minimized. Batteries and components around them should have proper spacing to allow cooling, and regular maintenance check-ups can be helpful in ensuring optimal operation.
NREL said that whenever possible, avoid repeated deep discharging of batteries, as the more it is discharged, the shorter the lifetime. If the home battery is discharged deeply every day, it may be time to increase the battery bank’s size.
Batteries in series should be kept at the same charge, said NREL. Though the entire battery bank may display an overall charge of 24 volts, there can be varied voltage among the batteries, which is less beneficial to protecting the entire system over the long run. Additionally, NREL recommended that the correct voltage set points are set for chargers and charge controllers, as determined by the manufacturer.
Inspections should occur frequently, too, said NREL. Some things to look for include leakage (buildup on the outside of the battery), appropriate fluid levels, and equal voltage. NREL said each battery manufacturer may have additional recommendations, so checking maintenance and data sheets on a battery is a best practice.
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wooh having just spent over $20,000 for an inverter system that can only power 5 items,which was eye opening in itself to now reading the batteries might last 10 years is all,well the installers said for another $20,000 I had room to put another battery in the box to power more things just eye opening we have a 926 sg ft house built in 1958 and for all that expensive money they won’t last as long as the solar panels do!
Yeah, no, that’s just not the case. First of all, what “inverter system” costs 20.000 dollars? A 3000VA inverter costs about 1.500 dollars, and that powers more than “5 items”. 10kWh of battery storage are around $3500-4000.
I got 30kWh installed 8 years ago and the system is still going strong, last time I checked I still got over 29kWh out of a full charge (which is probably partly because these rack units have a buffer). The batteries have effectively doubled my PV yield, and the entire system (+PV) paid itself off already. Heating the house with geothermal heatpump and absolutely loving it. But I get that burning stuff was mankinds greatest invention and is so ingrained in our culture that it’s really hard to get away from that.
Thank you for this article, although, in my opinion it falls short of identifying the best way to prolong the health of a battery back up system.
The strong advice of EV manufacturers and even Apple iPhone is to NEVER, OR AT LEAST RARELY WHEN YOU ARE PLANNING A LONG TRIP, CHARGE YOUR LITHIUM ION BATTERY TO 100%!
I have had my LG Chem battery for 4 1/2 years and only charge it to 80%.
I do the same for my Electric Vehicle and my iPhone. Regularly charging these batteries to 100% will shorten their lifespan…PERIOD!
I have tried for years to get responses from the Solar battery industry, and this magazine as to why they fail to educate customers to this fact and have yet to receive a reply?
Oh My!