Direct current (DC) power distribution has recently gained traction in buildings research due to the proliferation of on-site electricity generation and battery storage, and an increasing prevalence of internal DC loads. The research discussed in this paper uses Modelica-based simulation to compare the efficiency of DC building power distribution with an equivalent alternating current (AC) distribution. The buildings are all modeled with solar generation, battery storage, and loads that are representative of the most efficient building technology. A variety of parametric simulations determine how and when DC distribution proves advantageous. These simulations also validate previous studies that use simpler approaches and arithmetic efficiency models.This work shows that using DC distribution can be considerably more efficient: a medium sized office building using DC distribution has an expected baseline of 12% savings, but may also save up to 18%. In these results, the baseline simulation parameters are for a zero net energy (ZNE) building that can island as a microgrid. DC is most advantageous in buildings with large solar capacity, large battery capacity, and high voltage distribution.
Improvements in building end-use efficiency have significantly reduced the energy intensity of new buildings, but diminishing returns make it a challenge to build very-low energy buildings cost-effectively. A largely untapped efficiency strategy is to improve the efficiency of power distribution within buildings. Direct current (DC) distribution with modern power electronics has the potential to eliminate much of the power conversion loss in alternating current (AC) building distribution networks that include photovoltaics and DC end uses. Previous literature suggests up to 15 percent energy savings from DC power distribution in very energy efficient buildings with onsite generation and battery storage. This paper extends prior energy modeling of DC versus AC distribution in buildings, to consider the cost of implementing DC systems on a life-cycle basis. We present a techno-economic analysis framework that evaluates the cost-effectiveness of DC systems in U.S. commercial buildings, based on commercially available products for various PV and battery storage capacities. We use Monte Carlo simulation to account for uncertainty and variability in the cost inputs, and compute the payback period (PBP) and lifecycle cost (LCC) savings of DC versus AC distribution systems. We also conduct a sensitivity analysis to evaluate how future efficiency improvements in power converters and changes in electricity tariffs may affect LCC savings. This analysis shows that DC systems can be cost-effective in all scenarios that include large capacities of battery storage and onsite solar, whereas for systems without storage, DC distribution is generally not cost-effective due to lower energy bill savings.
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