TRIMET’S “VIRTUAL BATTERY” European aluminium business TRIMET has come up with a novel solution earlier this year, working with Bergishe Universitat Wuppertal to fit controllable heat exchangers to a run of 120 pots at its Essen plant, allowing pot temperatures to hold steady when power is diverted back to the grid.


TRIMET’s “virtual battery” allows it to significantly vary the amount of power used at the Essen smelter by +/-25% for up to 48 hours, releasing approx. 1,120 MWh which can be sold back to the grid on short notice (15mins) at times of peak prices, with a system efficiency of up to 95%.


Depending on time of year and time of day, the German quarterly hour power window typically varies from Euros 10 to 60/MWh, although extremes of Euros -200 to +1000/MWh have also occurred (the negative value occurs if the grid pays to get rid of excess power rather than risk damage).


TRIMET’s clever system helps balance the grid supply and demand, recharging when the price drops.


TRIMET has also lent space at their Hamburg site to wind turbine maker Siemens Gamesa, who are using surplus grid power to heat 1000 Mt of rocks to 600C, with the stored heat used to power a 1.5Mw steam turbine for 24 hours. The focus has been on optimising the shape and insulation of the rock container, with round trip efficiency of 25% expected to increase to 50% as the system is scaled up.


Over the past 20 years, global aluminium production has shifted to areas of cheap baseload power and lower environmental awareness. Under the baseload model, where aluminium smelters were run continuously, competition for power makes the US and Western Europe unlikely locations to build new smelters.


However, in a modern power system where wind and solar power are not consistently available and demand shows significant variation intra-day, the ability of TRIMET’s virtual battery to help balance a volatile market makes this an attractive addition to a modern grid.


Rohan Ziegelaar E: metals.desk@admisi.com T: +44(0) 20 7716 8081


12 | ADMISI - The Ghost In The Machine | September/October 2019


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