New tasks for old electric-car batteries

Old electric-car batteries must be taken back and recycled by the manufacturers. In this process, many materials are still lost. A pilot project organised by Vattenfall, BMW and Bosch in Hamburg is therefore testing the use of such materials after removal from electric cars.

A basic component for electromobility is the electric-car battery. But like all accumulators, the electric-car battery also loses charge capacity as the years pass. After six to eight years, the power drops below 80 per cent, and can therefore no longer be used for e-mobility, in which range plays an important role. But must it therefore be immediately disposed of?

No, says battery expert Daniel Hustadt. With its replacement, the used battery starts its second life. Instead of being recycled at considerable expense or ending up on the rubbish heap, it can still be used meaningfully and economically with its almost 80 per cent charge capacity. Hustadt should know. He is a project manager at Vattenfall Innovation GmbH and responsible for large battery power stores. There is such a large power store in the port of Hamburg, where the energy company Vattenfall, in cooperation with the car manufacturer BMW and the technology company Bosch, is testing the scope for reuse of electric-car batteries. 

Keeping the power supply stable

In a 26-metre-long and roughly six-metre-wide concrete low-rise building, the battery modules from around 100 electric cars are linked together. Converters convert the direct current of the batteries into alternating current, which can then be fed into the electricity grid, as electricity that does not serve for direct consumption, but is intended to maintain the voltage in the power supply at a stable level.

This so-called control energy is always required when there is either too much or too little electricity in the grid. The magic line is at around 50 Hertz. Only minimal deviations from this supply frequency are permissible. 

"It's like a bath-tub that must constantly maintain the same level. The tap's running and the plug's open. And the water level must be kept constant, otherwise there's the risk of the supply collapsing," says Hustadt. 

It's easy as long as the quantity of electricity produced corresponds to the amount used. But as soon as a power plant drops out of service, or the renewable energy sources deliver less electricity, for example because the wind has dropped, the balance must be recovered by other power generators. In face of all the challenges, the power supply must remain stable, in every second the overcapacities are compensated or increasing demand is met.

Rethinking electricity management

Until now, the large power stations have compensated for these fluctuations. But in future there will be fewer and fewer of them, and the changeover to a renewable energy supply is a matter of political will. 600 to 700 megawatts of primary control power are currently required to compensate for the daily fluctuations in the German electricity grid. Two megawatts can be supplied or compensated for by the small pilot system. "Larger battery power store systems can also compensate for or provide more electricity," says Hustadt. However, he continues, there are not yet enough electric cars and old batteries to already allow the economical use for bigger 2nd-life large battery power stores. We cannot yet envisage when this will be the case.

But so much is clear: The change to alternative energy sources, to renewable energy, is also a rethinking of electricity management. Sun, wind and water do not provide a constant amount of power, and a wind power station, for example, cannot simply react to fluctuations in demand. In future, this will mean for the energy companies the increased need of power stores, as in the port of Hamburg. And a new task for old electric-car batteries.

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