German firm turns aluminium smelter into a ‘Virtual Battery’

Trimet, Germany’s largest producer of aluminum, is testing technology to turn its smelters into a "virtual battery" capable of delivering 1.12 gigawatt-hours of flexible capacity.

The family-owned business is investing €36 million ($39 million) in a two-year industrial-scale pilot of systems that will allow power use across 120 electrolysis cells to be dialed up or down by 25 percent in either direction, for up to several hours.

The pilot is being carried out on a single production line in Trimet’s Essen aluminum smelter.

The production line will be able to compensate for fluctuations in the power grid, making it easier to manage intermittent renewables. The virtual battery concept relies on adjustable heat exchangers, developed with help from the University of Wuppertal in North Rhine-Westphalia, that can maintain the energy balance in each electrolysis cell irrespective of changing power inputs.

The technology also ensures that power fluctuations do not affect the magnetic fields in the electrolysis cells. The capacity of the test production line alone is comparable to a medium-sized pumped-hydro storage power plant.

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“With an efficiency rate of 90 to 95 percent, the virtual battery is a lot more efficient than technologies such as power-to-gas or compressed-air reservoirs,” said a source within the company. “Furthermore, no new power lines are needed, as the smelter is already integrated in the high-voltage grid."

As a major industrial power user, Trimet already participates in German demand response programs, taking its aluminum smelters offline for short periods when required to stabilize the grid in the face of load surges.

According to a 2014 Bloomberg report, the company uses 14 megawatt-hours of energy to make each ton of aluminum.