The tower in Berlin. Image: Vattenfall. Swedish public utility Vattenfall is about to start filling a 45m-high, 200MW-rated thermal energy storage facility with water in Berlin, Germany. The heat storage tank can hold 56 million litres of water which will be heated at 98 degrees celsius and will be combined with the existing power-to-heat system of Vattenfall’s adjoining Reuter West power plant.