Review of DC Power Distribution in Buildings: A Technology and Market Assessment

California's energy policy envisions a future energy landscape that can best be realized through a highly integrated and interoperable grid with very energy efficient end uses combined with on-site energy generation and storage. Direct current (DC) power distribution architectures have been proposed as a way to integrate the various electrical components within buildings that are needed to realize this vision, at a lower cost than traditional alternating current (AC) power systems. This report's purpose is to summarize the current state of knowledge about the feasibility, cost effectiveness, market barriers, customer needs, and savings potential for DC or hybrid DC-AC systems to power zero net energy (ZNE) residences and commercial buildings, subdivisions, and communities. Particular focus is on residential and light-commercial building applications.

The all-AC power systems in use today were developed during a time when nearly all power generation and end-use devices were natively designed for AC power. Increasingly, however, our power systems need to integrate resources and loads that are natively DC: distributed generation, storage (batteries), and end-use devices (electronics, DC motors with variable-speed drives, etc.). DC offers an ideal integrating platform for these modern power components; offering energy savings and improved reliability with potential for lower first cost. Furthermore, the efficiency, reliability, and ease of control of DC power distribution could be a low-cost element to achieving ZNE buildings, thus helping California meet its ZNE and global climate change goals.

Various aspects of DC electrical systems—including DC microgrids, data centers, residential appliances, batteries, fuel cells, lighting, electronics, communications, and renewable sources—have been studied or promoted by industry. These studies and other industry efforts generally conclude that DC power offers energy savings, potential for lower capital cost, and power quality and reliability improvements. These results are similar to those found with high-voltage DC (HVDC) transmission systems used in the United States, Europe, and Asia. However, there is very little performance information on DC systems in U.S. residential or commercial buildings.

This report first starts with a review of existing academic and market literature on the design, availability, and performance of DC distribution systems and equipment in buildings. It then summarizes new information collected during the course of this study through a stakeholder workshop, and a survey and in-depth interviews conducted with power system researchers, designers, and manufacturers. The report concludes with a summary of the findings and suggested next steps based on all the information compiled and collected.