Battery Energy Storage System for Frequency Control and Fast Peak Shaving - Case Helsinki - Pirjo Heine; Atte Pihkala; Hannu-Pekka Hellman; Kristiina Siilin; Suvi Takala; Pia Ruokolainen; Minna Laasonen (2019 IEEE PES Innovative Smart Grid Technologies Europe, ISGT-Europe 2019, Bucharest, Romania, September 29 - October 2, 2019, 2019)