German energy company Uniper SE (<a href="https://www.boerse-frankfurt.de/equity/uniper-se-na-o-n-1" target="_blank">ETR:UN0</a>) on Monday said it will build a 50-MW/100-MWh battery energy storage system at the Heyden power plant site in Petershagen in the northwestern German state of North Rhine-Westphalia in partnership with Slovenian battery system provider NGEN.