Simulation to optimize a DC microgrid in Okinawa

In December, 2014, we installed a DC microgrid system in the campus village at the Okinawa Institute of Science and Technology and the system has been operational continuously for the past 16 months. This microgrid system was designed to exchange energy among houses using DC so as to utilize surplus energy before the rechargeable batteries reach full capacity. Data obtained in this real environment were used to create a simulator that enabled us to determine the optimal configuration of this microgrid based on current PV and battery costs and predicted future costs. The simulation shows optimal structure of this DC microgrid is 4.6 kW PVs and 3.6 kWh battery per house with total installation costs of 0.5 M US$. In the future it should be possible to reduce installation costs based on the predicted PV and batteries price. Cost recovery period should be reduced by 42% while achieving the self-sufficiency ratio of the present DC microgrid. More PVs and batteries are installed, the recovery period will diminish further still.