Energy and Cost Benefits of DC Power in ZNE Buildings

Improvements in building end-use efficiency have significantly reduced the energy intensity of new buildings, but diminishing returns make costeffective zero-net energy (ZNE) buildings a challenge. 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. Previous literature suggests up to 15% energy savings in DC ZNE buildings with onsite generation and battery storage. Nonetheless, DC faces a market disadvantage against AC, and the benefits of DC distribution must be compellingly demonstrated before wide adoption. This paper presents recent modeling of DC vs. AC distribution in buildings, based on detailed load and generation profiles, wire losses, and power conversion efficiency curves. Our analysis shows that annual energy savings can range from approximately 8% of baseline electricity use in an office with PV and no battery, to approximately 15% in a building with a large PV array and battery. This paper also presents a techno-economic analysis framework that evaluates the cost-effectiveness of DC systems in several commercial buildings based on commercially available products. Based on a Monte Carlo analysis, we find that DC systems can be cost effective in all scenarios that include battery storage and onsite solar, whereas for systems without storage, DC distribution is not cost effective.