Impact of AC vs DC Distribution on System Efficiency in a Nanogrid Office

Abstract

Reunion Island is a French overseas department located in the southwestern part of the Indian Ocean. Due to its geographical location, it needs to develop local sources of energy production, such as solar energy, to achieve energy autonomy. By reducing energy conversion steps, LVDC (Low-Voltage Direct Current) nanogrids can contribute to this objective by reducing the energy consumption of buildings and optimizing electrical installations. This paper proposes a hybrid nanogrid architecture currently deployed in an office building in Réunion island. The hybrid nanogrid includes a PV power plant, a LiFePO4 battery, a LVDC distribution (48VDC loads such as lighting and fans) and an Alternating Current (AC) distribution for experimentation. To evaluate the overall nanogrid efficiency and optimize its lifetime, a method to measure the global efficiency of the system in AC or DC distribution for an identical final load and section cable is presented. Results have shown a total efficiency gain of 18% in DC compared to AC distribution, for certain conditions described in the paper. Voltage drop and battery capacity during discharge have also been measured to complete the results.