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 idea here is to maximize the value of the home’s solar system. And, some batteries are optimized to integrate an electric vehicle charger.
Although deployment of energy storage is on a steady climb, attachment rates of batteries remain low: in 2020 8.1% of residential solar systems attached batteries, according to Lawrence Berkeley National Laboratory (LBL).
Many options exist with multiple battery chemistries available for home energy storage. Bottom line, however, is that in the United States two brands dominate the space. More than 90% of the market is served by LG Chem and Tesla Powerwall, which are lithium-ion batteries, according to LBL. Tesla has more than 60% of the entire market share.
The Tesla PowerWall has a limited warranty that says the device will be free from defects for 10 years following installation. It also warrants that the PowerWall will start its life with a capacity of 13.5 kWh, and will retain energy capacity based on a degradation schedule.
LG warrants that its system will retain at least 60% of its nominal energy capacity (9.8 kWh) for 10 years. The battery must operate between -10 degrees Celsius and 45 degrees Celsius to remain warranted. Total throughput of energy within the warranty is limited to 27.4 MWh.
Life of a battery
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.
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.
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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I like the NREL’s idea of how to determine you need a bigger battery bank. From my experience I can offer a simplified version. Whatever you calculate will be an adequate battery bank, double it. It won’t be enough, but you won’t be as disappointed as you otherwise would have been!
First everyone should know they have little clue how long any lithium battery will last as none have.
Next the BMS likely will limit battery life.
And no mention of the battery still doing the majority of storage and the best buy now, lead. At $100/kwh golf cart well shopped vs $600/kwh for a Powerwall and lasts 5 yrs the economic choice is clear.
By the time in 5-6 yrs they need replacing lithium will be under $200/kwh saving 50% and 5 more yrs of battery.
A vanadium flow battery lasts an average of 25 years and zero risk of fire. Management is simple and maintain certain is low and monitored, the anode and cathode are both vanadium, which never degrades and power stack can be swapped every 10 years if you want to upgrade. Energy storage capacity can be added at a ratio of 12X capacity to power ratio. Ie. if you need 12x the capacity, simply add tanks of electrolyte not the entire battery every time you want another hour of capacity. Additionally a vanadium battery is climate positive if the vanadium is produced sustainably and as it lasts forever it is also a store of wealth that deceases the cost of energy to virtually nothing over time.
What is the reason thst nobody mentioned ever comment on super capacitors. It will basically last for more than 1 million cycles.
It can be fully recycled a and is environmentally friendly.
Compare that to any other power storage systems, this in my opinion, beats all other competition.
Any comments ?
Hi P Naude,
Super cap are great for exactly the reasons you mentioned but they lack energy density and they are very expensive. Costs have been coming down and power density going up but not anything close to the lithium Ion.
Both the LG and Tesla batteries are Nickel-manganese-cobalt (NMC), used in most electric cars since they have the best energy density by weight. They use expensive materials, including conflict minerals (ie cobalt), they don’t have a great cycle lifetime, and there is a safety risk. But weight is not a big deal for stationary storage, which is why Tesla is now using lithium-iron-phosphate (LFP) for their Megapack utility-scale batteries. LFP uses cheaper materials, is safer, and has a better lifetime. They are starting to show up in residential batteries, and I think we’ll see a lot more of them in time.
Yes, I think that’s the chemistry used in the Enphase batteries btw. They specifically chose that because it is safer and has a better lifetime.
Coremax Powerwall is rated for 15 + years. because lifepo4 battery life is super long
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