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Simultaneous distribution of AC and DC power

National Renewable Energy Laboratory

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Technology Marketing Summary

According to the U.S. Energy Information Administration’s 2010 International Energy Outlook, solar energy is expected to grow globally by 12.7% per year until 2035; more than any other renewable energy source. The growth of on-site DC (Direct Current) power in new and existing buildings has significant energy savings potential through the elimination of inverters necessary to convert DC source power into AC (Alternating Current) as well as the elimination of equipment normally used to reconvert AC back to DC for components of HVAC systems, and most Miscellaneous Electrical and Electronic Loads (MEELs). The inefficiencies introduced by this unnecessary double power conversion (inverters and the subsequent AC to DC converters for DC power supply) could be eliminated through the introduction of an additional dedicated DC only wiring infrastructure. However, this solution adds significant capital costs introduced by the need to basically double the electrical wiring, moreover it is only applicable to the design of new buildings.


This invention makes use of Pulse-Width Modulation (PWM), Time-Division Multiplexing (TDM), and Power Multiplexing and Demultiplexing (MUX/DEMUX) concepts to chop, combine, transport, separate and reconstruct both AC and DC power over a single existing wire.

PWM is an electronic power switching technique for regulation of AC and DC power in a efficient way. The AC power’s sine wave is chopped into many slices through fast electronic on/off switching (tens of thousands of on/off cycles per second). The chopped wave is filtered and the resulting sine wave is applied to the electrical load.

TDM is a concept where multiple signals are simultaneously transmitted over a single information medium such as a wire. The physical medium is time-shared amongst all signals through the allocation of cyclical timeslots of fixed length that are exclusively dedicated to each respective signal. The building blocks of TDM buses are the MUX and DEMUX devices. A MUX selects one of many input signals and forwards the selected input into a single output line. A DEMUX performs the inverse, by separating the signals at the input and forwarding them on to separate output lines.

AC and DC power sources are each individually supplied to the system and chopped at the same frequencies. The AC “off” periods correspond to the DC “on” periods. The power sources are then multiplexed through a high frequency power MUX and applied to an existing building wiring infrastructure (the TDM power bus). At utilization a device separates the DC from the AC via a high frequency power DEMUX. The resulting separated AC and DC signals are reconstructed at voltages roughly half of the source voltages. To compensate for this lower voltage at the load, a transformer can be inserted at the AC source before it is combined with the DC power at the MUX, allowing for the delivery of the required nominal voltage. The DC voltage at the source must be at least double the level of the highest planned load voltage at the utilization load.

Patents and Patent Applications
ID Number
Title and Abstract
Primary Lab
Patent 9,136,708
Simultaneous distribution of AC and DC power
A system and method for the transport and distribution of both AC (alternating current) power and DC (direct current) power over wiring infrastructure normally used for distributing AC power only, for example, residential and/or commercial buildings' electrical wires is disclosed and taught. The system and method permits the combining of AC and DC power sources and the simultaneous distribution of the resulting power over the same wiring. At the utilization site a complementary device permits the separation of the DC power from the AC power and their reconstruction, for use in conventional AC-only and DC-only devices.
National Renewable Energy Laboratory 09/15/2015
Technology Status
Technology IDDevelopment StageAvailabilityPublishedLast Updated
NREL 10-35 U.S. Issued Patent 9,136,708DevelopmentAvailable06/24/201106/28/2011

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To: Erin Beaumont<>