Studi Pengaruh Pemasangan Battery Energy Storage System (BESS) Secara Terdistribusi Sebagai Ancillary Services untuk Memaksimalkan Penetrasi PLTS pada Jaringan Distribusi Tegangan Menengah = Study on the Impact of Distributed Installation of Battery Energy Storage Systems (BESS) as Ancillary Services to Maximize Solar Photovoltaic Penetration in Medium Voltage Distribution Networks