Energy savings from direct-DC in U.S. residential buildings

An increasing number of energy-efficient appliances operate on direct current (DC) internally, offering the potential to use DC directly from renewable energy systems, thereby avoiding the energy losses inherent in converting power to alternating current (AC) and back. This paper investigates that potential for net-metered residences with on-site photovoltaics (PV) by modeling the net power draw of a 'direct-DC house' compared to that of a typical net-metered house with AC distribution, assuming identical DC-internal loads. The model comparisons were run for 14 cities in the United States, using hourly, simulated PV-system output and residential loads. The model tested the effects of climate and battery storage. A sensitivity analysis was conducted to determine how future changes in the efficiencies of power system components might affect potential energy savings. Based on this work, we estimate that net-metered PV residences could save 5% of their total electricity load for houses without storage and 14% for houses with storage. Direct-DC energy savings are sensitive to power system and appliance conversion efficiencies but are not significantly influenced by climate.