Understanding the potential for electricity savings and assessing feasibility of a transition towards DC powered buildings

Panel: 5. Energy use in buildings: projects, technologies and innovation

This is a peer-reviewed paper.

Authors:
Brock Glasgo, Carnegie Mellon University
Ines Azevedo, Carnegie Mellon University, USA
Chris Hendrickson, Carnegie Mellon University, USA

Abstract

Advances in semiconductor power electronics and growing direct current loads in buildings have lead researchers to reconsider whether buildings should be wired with DC circuits to reduce power conversions and facilitate a transition to efficient DC appliances. The feasibility, energy savings, and economics of such systems have been assessed and proven in data centers and commercial buildings, but the outcomes are still uncertain for the residential sector.

In this work, we assess the technical and economic feasibility of DC circuits using data for approximately 600 homes in Austin, Texas to understand the effect of highly variable demand profiles on DC-powered residences. With appliance-level use and solar generation data, we use Monte Carlo simulation to quantify costs and benefits of this technology.

Preliminary results show energy savings between 0.2-2.2% by reducing conversion loss when solar PV is distributed as DC. With battery storage, savings increase to 0.5-4.3%. These results are significantly less than similar studies using simulated loads, potentially indicating that previous models overestimate savings by not accounting for the variability of actual home loads. When efficient DC appliances are modeled, savings increase to 7.1-17% of home consumption. Additional cost reductions of appliances and PV systems due to reduced power electronics have not yet been estimated, but the scale of early energy cost savings suggest a transition to DC may only be cost-effective in new construction.

The AC circuits in today’s buildings took over 120 years to develop, so a transition to DC will not be without challenges. Voltage standards that safely and efficiently serve variable loads have to be established. Installation and maintenance procedures have to be adapted to DC. Utility billing and incentive programs have to be designed for new standards. Manufacturers have to respond with output to establish economies of scale. And electrical codes will have to account for all of this. By assessing these factors and quantifying their effects on the monitored homes, an improved understanding of a transition to increased use of DC power will be gained.