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.

1 aGerber, Daniel, L.1 aVossos, Vagelis1 aBrown, Richard, E.1 aFeng, Wei1 aMarnay, Chris uhttps://china.lbl.gov/publications/energy-and-cost-benefits-dc-power-zne02029nas a2200265 4500008004100000022001300041245011000054210006900164260001200233300001400245490000800259520122500267653002501492653001901517653001501536653001301551653001501564100002301579700002001602700001401622700001801636700001901654700002301673856006701696 2018 eng d a0306261900aA simulation-based efficiency comparison of AC and DC power distribution networks in commercial buildings0 asimulationbased efficiency comparison of AC and DC power distrib c01/2018 a1167-11870 v2103 aDirect 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.

10acommercial buildings10adirect current10aefficiency10amodelica10asimulation1 aGerber, Daniel, L.1 aVossos, Vagelis1 aFeng, Wei1 aMarnay, Chris1 aNordman, Bruce1 aBrown, Richard, E. uhttps://china.lbl.gov/publications/simulation-based-efficiency02504nas a2200253 4500008004100000022001300041245007800054210006900132260001200201300001400213490000800227520172000235653002401955653002001979653001701999653001902016653002902035100002002064700002302084700002902107700002302136700001802159856007302177 2018 eng d a0306261900aTechno-economic analysis of DC power distribution in commercial buildings0 aTechnoeconomic analysis of DC power distribution in commercial b c11/2018 a663 - 6780 v2303 aImprovements 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% 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.

A techno-economic analysis framework based on commercially available products that evaluates the cost-effectiveness of DC systems is presented. The analysis is conducted for three commercial building types in two California climate zones and for various PV and battery storage capacities. Monte Carlo simulation is used to compute the payback period and lifecycle cost savings of DC versus AC distribution systems. A future-market scenario is also examined, which evaluates how future efficiency improvements in power converters and changes in electricity tariffs may affect cost 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.

10acommercial building10aDC distribution10aDC microgrid10adirect current10aTechno-Economic Analysis1 aVossos, Vagelis1 aGerber, Daniel, L.1 aSmires, Youness, Bennani1 aBrown, Richard, E.1 aMarnay, Chris uhttps://china.lbl.gov/publications/techno-economic-analysis-dc-power