The extended lifespan is decisive for the quality, economy and sustainability of batteries – as well as for the use of storage systems in virtual power plants. In its own tests, sonnen has now achieved significantly longer lifetimes than previously assumed.
Wildpoldsried, July 14, 2021 - How long do batteries actually last? This question is crucial for the use of batteries in energy storage systems. The longer the service life, the more economical and sustainable their use is.
Since there has been little long-term data on the life of batteries in energy storage systems, sonnen has, for many years, operated its own battery laboratory at its headquarters in Wildpoldsried. To really find out if a battery can deliver on its promises, it has to be charged and discharged again and again for years. In the lab, batteries from different manufacturers are tested over long periods of time and their service life is measured.
A performance test, running for almost 8 years now, has now shown that a lithium iron phosphate (LFP) battery type used in the sonnenBatterie has exceeded 28,000 charging cycles already. This means that a single battery cell was fully charged and discharged 28,000 times – without reaching the end of its service life. ¹ In fact, the battery still retained 65 percent of its original capacity.
In sonnen's battery lab, the LFP battery cell was subjected to much harsher conditions than would be usual for a household power storage unit. It was fully charged and discharged several times a day, which puts more strain on the battery. The test was also carried out with a C-rate of 1 and 100 percent depth of discharge (DOD), meaning the was fully charged within one hour and fully discharged again within one hour.
In everyday life, however, less than one complete charge and discharge per day is usual - in Germany, a home storage battery completes around 250 charge cycles in a year – less than 1% of the cycles now measured in the lab.
"The test results achieved so far exceed the lifetime predictions of the battery technology we use. This is an important confirmation of quality for our customers. And those who have a long-lasting battery also benefit from it for longer economically," says sonnen CEO Oliver Koch and adds: "This also allows us to prove that this is the right technology for our virtual power plant, which charges and discharges the batteries in addition to self-consumption."
Parallel to the individual battery cell, sonnen is also testing battery modules for long terms. A sonnen battery module consisting of over 200 battery cells of the same type has already achieved over 10,000 charging cycles.
The longer a battery lasts, the more efficient it is. A battery that can be charged and discharged 10,000 or 20,000 times can provide much more energy with the same use of resources than less durable batteries.
Although the test of a single battery cell or module cannot be generalized for every sonnen product, it is an important proof point for the quality of its storage systems.
¹ The end of life for lithium-ion batteries occurs when the available capacity drops rapidly.