Direct Current as an Integrating and Enabling Platform for Zero-Net Energy Buildings

There is increased interest in using direct current power distribution within zero-net energy buildings to connect very efficient end-use equipment, such as solid-state lighting and variable speed motors, with on-site solar generation and energy storage. While the potential benefits of direct current technology – such as reduced energy conversion losses and improved power quality – are attractive, there is a lack of information and experience with implementing direct current systems in buildings. This report addresses this information gap, presenting the results of a scoping study of direct current in very efficient, or zero-net energy, buildings. The study assessed the current state of technology and markets for direct current power to identify barriers and opportunities for adoption of this technology in the building sector. The assessment found a general consensus in the literature that direct current can save energy, while the key barriers to adoption are higher cost, a lack of direct-current compatible products, and relative inexperience among building designers, engineers, and contractors. The study team then used the information compiled through the market and technology assessment to develop a set of guidelines and templates for “early adopter” building owners and designers to use in implementing direct current in buildings today. The design templates reflect that direct current options are available for nearly all building end uses, particularly lighting and electronics. The whole-building guidelines developed in this study reflect best practice power architectures for direct current distribution in buildings, based on energy modeling and life-cycle cost analysis. The energy modeling showed potential energy savings of zero to 15 percent of baseline electrical energy use, with higher savings for buildings with photovoltaics and large battery storage, and when on-site solar production is coincident with power demand. This study shows good potential for direct current in commercial buildings, with a need for more demonstrations and standardization to ease barriers and speed adoption.