Optimizing 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 power from renewable energy systems directly and avoiding the 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 the "direct-DC house" with respect to today's typical configuration, assuming identical DC-internal loads. The power draws were modeled for houses in 14 U.S. cities using hourly simulated PV-system output and residential loads. The latter were adjusted to reflect a 35% load reduction representative of the most efficient DC-internal technology based on an analysis of 32 electricity end-uses. The model tested the effect of climate, electric vehicle loads, electricity storage, and load shifting on electricity savings; a sensitivity analysis was conducted to determine how future changes in the efficiencies of power system components might affect savings potential. National average direct-DC savings of 5% were estimated for configurations without storage and 14% for configurations with storage. Load shifting did not have a significant positive effect on savings, and the electric vehicle reduced the incremental savings compared to the same house configuration without it. The estimated savings were affected by the power system and appliance conversion efficiencies but were not significantly influenced by climate