Using old car batteries for power storage

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Renewables International

German engineering organization VDE has released a comprehensive study on the “second life” of car batteries for grid-attached power storage. The potential is tremendous and affordable.

In a new study (in German), the VDE points out that discarded car batteries still have a residual capacity of 80 percent and would only cost 50 percent as much as new batteries. For primary ancillary services, the value would increase by 26-33 percent.

The tap this potential, however, numerous steps would need to be taken. Batteries from different manufacturers – even using basically the same technology – age differently, and combining them in one storage system is not trivial. The aging processes would therefore need to be carefully tested so that second-life batteries with roughly the same performance could be grouped together. In addition, the further aging of these batteries would need to be delayed to the extent possible during their second life.

Interestingly, although Germany has some 44 million vehicles on the road, all of them with at least one battery, the study focuses on the potential of batteries from electric vehicles and hybrids. Most of the studies investigated in the overview of current literature reveal that Germany is unlikely to reach its goal of 1 million electric cars on the road by 2020, but the situation may look considerably different in 2030. As of August 2015, only 6,456 fully electric cars were on the road in Germany along with 6,493 plug-in hybrids.


One important thing to keep in mind here is that these batteries will not be constantly discharged down to their minimum and fully charged again. Rather, with ancillary services, we are talking about short phases of small charging and discharging – see my previous article on grid-connected battery storage systems from Younicos.

In 2014, 8.14 million conventional vehicles were unregistered in Germany, roughly twice as many as new cars were added, which seems to be a strange development; the German vehicle fleet apparently shrunk by nearly 10 percent. But the number itself shows how many lead batteries are already available. Nonetheless, the study focuses on the lithium batteries used in electric vehicles; apparently, the potential of lead batteries for second-life usage is too limited. The study says that lithium-ion batteries have “considerable advantages” over lead batteries aside from price, so the study is essentially forward-looking: the large number of lithium-ion batteries to come will increase the potential of second-life battery storage. Keep in mind that, while conventional cars only have a single lead battery, an electric car has far more storage capacity, so a single electric vehicle will produce the second-life potential of dozens of conventional cars.


The first life of car batteries reaches around 800 full cycles. By that time it, the battery has reached 80 percent of its original capacity (marked by a gray X in the chart). The second life begins at that point and adds on another roughly 200 full cycles – but keep in mind that the timeframe is longer because the batteries will not at that point be constantly fully charging and discharging, but rather constantly charging and discharging in small increments to provide ancillary services to the grid.

Perhaps the most interesting chart is this overview of and-of-life batteries from 2010. The largest number (in terms of tonnage) was from UPS systems (uninterruptible power supply – USV in the German). But in second place at 29.3 percent comes a vehicle type rarely talked about: forklifts. These machines generally run indoors (so emissions are a huge issue) and do not have to cover long distances (so range and the availability of charging stations are not a problem). Electric railway vehicles only make up 12.3 percent of the total.
The study has 156 pages, so I obviously cannot do it justice here. If you speak German, check it out for yourself!
Source: Renewables International. Reproduced with permission.


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  • Alan S

    Good article. Also we need car and stationary storage batteries that can be restored with minimal waste so the innards are replaced and the casing retained.

    But how does the statement ‘Electric railway vehicles only make up 12.3 percent of the total’ relate to batteries? I know there’s a revival of interest in battery powered railcars going on in Britain at present, Does Germany already have these in operation?.