In Indonesia, QSG has successfully built and developed the 10 MW operated Isimu Solar Power Plant Photovoltaic (PLTS Isimu) since January 2020; located in Isimu region, Gorontalo Province, Indonesia. In the future, QSG planned to develop and built more renewable energy power plant by expanding the existing PV Plant for the same capacity and location as the previously built PLTS Isimu. By expanding the project, Isimu SPP PV expansion (PLTS Isimu Expansi) will be connected to Isimu Switchgear as well as Isimu SPP PV connection. Another issue is intermittency: one of the main challenges in PV farm operation. Its power fluctuation can disrupt the grid frequency, which has been proven to be a problematic case for a safe and reliable grid operation. To ensure a smooth operation of PLTS Isimu Expansion Project, the optimal BESS design need to be determined in order to make sure that the equipped BESS will be able perform its function as ramp rate control/ smoothing properly to help mitigate the intermittent nature of the PV Farm that depends on solar irradiation. This BESS utilization will also provide additional comfort for PLN as the system operator.