A second life for old batteries

29. October 2020

Even when lithium-ion batteries become too feeble for use in electric cars, they are still a long way away from having to be scrapped. Before they must be consigned to the recycling plant , they can still be used as a stationary power storage system for several more years. This also serves to make them more environmentally sound.

When the floodlights go on in the evening in the Johan Cruyff Arena in Amsterdam, the sun also plays its part. 4,200 photovoltaic modules have been installed on the roof of the home stadium of Ajax Amsterdam to convert solar energy into electricity. As it is a well-known fact that the sun doesn’t shine at night, the solar energy thus generated also has to be stored. For this purpose, a battery storage system with a capacity of three megawatts has been installed in the arena's car park – enough to power 7.000 Amsterdamer Housholds for a whole hour.

In the event of power outages, the battery storage system kicks in with its emergency supply, reducing the use of diesel generators and relieving the power grid of strain by balancing out the peaks that occur, for example, during concerts. This is made possible by the 85 new and 63 old batteries from Nissan's electric car, the Leaf, which are put to work inside the large store.

When batteries are no longer powerful enough for use in cars, they still have 70 to 80 percent of their original capacity. In this condition, then, it makes neither economic nor ecological sense to break them down into their component parts. At the end of their mobile lives, they can instead continue to offer a valuable service in a static position, as they do in the football arena in Amsterdam. After all, with a fixed energy storage system, unlike in an electric car, it is less important to accommodate as much storage capacity as possible in as small a space as possible. 

In stationary operation, the aged batteries are also significantly less stressed than in an electric car, where they are constantly being pushed to their limits in both acceleration and recuperation – i.e. in the process of energy recovery during braking. Overall, stationary operation is a much more even business. Charging and discharging is slow and therefore much kinder to the battery. This is also good for the service life of the batteries. Laboratory measurements of ageing processes have shown that batteries can continue to be used for a further 10 to 12 years in their “second life”. In other words, a battery which sees average use will not have to go for recycling for over 20 years. 

Anyone who gives these electricity storage systems a second life in this way “will be retroactively improving the environmental balance of electromobility,” Streetscooter founder Achim Kampker from RWTH Aachen University tells the newspaper Die Welt. This is because the additional years of useful life are not currently included in environmental balance sheets.

Automakers are legally obliged to take back their old car batteries. The “second life” idea offers a great deal of potential, economically as well as ecologically, according to a study by consulting firm Berylls Strategy Advisors. As the study has it, by 2032 a battery capacity of at least 1,522 GWh from used batteries is expected to be available for use in stationary operation. So, it’s hardly surprising that there has been such a proliferation of second life projects in recent years: Volvo, for instance, has deployed used batteries from its electric buses in two  residential complexes in Gothenburg. The old batteries are charged here by solar systems installed on the roofs of the various buildings. The stored electricity then supplies electrical energy to washrooms, outdoor lighting and other public areas.

In May last year, Audi installed a storage system with e-tron batteries at the Euref-Campus in Berlin  The 1.9-Mwh storage system serves as a buffer for the on-site fast charging stations where electric cars can recharge their batteries.

Vattenfall, Bosch and BMW installed this type of super battery in the Port of Hamburg back in 2016. This battery storage system made from retired batteries from BMW’s i3 electric car, with its capacity of 2.8 megawatts, could power an average two-person household for seven months. In practice, however, it is primarily used to compensate for fluctuations in the electricity grid.  

Until now, these control services have mainly been provided by pumped storage power plants. The advantage of battery storage systems, however, is that they can absorb energy quickly and release it in milliseconds with very low losses. And they can be installed almost anywhere relatively quickly. However, their capacities are still comparatively low. Whereas Daimler’s  largest battery storage system, which is situated in Lünen near Stuttgart and is the world's largest battery storage facility to date, has a capacity of 13 megawatt hours, the Goldisthal pumped storage plant, for example, boasts more than 8,000 megawatt hours.

One reason for this is the poor availability of old batteries. After all, a battery can power a car for eight to ten years – an age which most of today’s electric vehicles have not yet reached. But that is set to change in the coming years, and the number of used batteries will increase significantly. The old batteries could then also increasingly be pressed into service again in a second life as electricity storage for private households with solar panels. For example, a battery with a capacity of 20 kWh can store more energy than is usually needed as a buffer in a family household – so it follows that a battery from the small VW e-Up with its power rating of 32 kW would be more than sufficient. Retired batteries are also being discussed as an emergency power storage option in hospitals or critical infrastructure.

However, not all old batteries are capable of living a second life. Investigating the state of health of a battery currently takes around three hours and costs a lot of money, because expensive measurement technology is used. The University of Warwick has now developed a method for Nissan which makes it possible to vastly speed up the analysis of the batteries. The method, which takes just three minutes, can be used to determine whether the used battery can still be used as a “spare parts warehouse” for other electric cars or as an alternative for second-life use, or whether it should simply go straight for recycling. The process is now going to be extensively tested in a pilot plant. Thanks to this new procedure, Nissan hopes to be able to reuse the majority of those batteries which are currently in its electric cars in Europe.