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An EPRI White Paper

DC Power Production, Delivery and Utilization

Is the DC-powered house a fantasy or could it be a future reality?, continued

AC voltage to DC and then back again to a variable frequency AC, where the frequency is directly related to the speed of the motor. The VFD inherently uses a DC bus, so why not supply it directly

with DC instead of AC?

Use of VFDs is on the rise, since controlling the speed of the motor to match demand can not only save energy but also optimize func- tion. For example, being able to fine tune the motor speed of an air conditioner, and thus functions such as fan speed and air flow, can make room temperatures and conditions more comfortable.

As motor-operated loads become increasingly controlled through VFDs –very little will remain in a house that really needs AC power. If both electronics and motors operate on DC—the question be- comes just how much can be accomplished by having DC low-volt- age wiring in a house? Some opportunities and issues to consider:

  • Energy savings. If the numerous times AC is converted to DC are reduced, savings of as much as 10% of overall energy consumption are possible.

  • Conversions for varying DC voltages. Elimination of AC to DC conversions does not obviate the need to convert one DC voltage to another.Various devices and components of appliances rely on different DC voltages. This could remain an obstacle, but an option is to stan- dardize on one DC voltage, as we were able to stan- dardize on 120V AC.

  • Interconnection of onsite generation and storage.A ma- jor, and often overlooked, advantage of DC is the ease of interconnecting generating or energy storage resources. Consider the ease of taking two DC batteries and con- necting them together.Then consider trying to do that with two small AC generators from the local hardware store. The Achilles heel of distributed generation is in- terconnection and integration, which can be overcome with DC power delivery.

  • Onsite generation sources. Perhaps the biggest advan- tage of DC powering is that most of the distributed generation and energy storage sources—whether solar panels or fuel cells or microturbines or batteries—are inherently DC sources. You can connect your rooftop solar panel to a home’s DC wiring. And when you can finally buy that plug-in hybrid electric vehicle at the local

dealership—why not plug that in to your DC outlet? Your car can either be charged—or be run as a genera- tor to power the house.

  • DC power delivery from an Intelligent Universal Trans- former. Your friendly utility may someday provide you with DC power as well as AC, using the EPRI Intelli- gent Universal Transformer (IUT). The IUT, which is an emerging, revolutionary technology, can directly provide low-voltage DC from the utility

  • Smart home energy management.As home controls get smarter and digital communication systems advance, we can imagine deployment of an intelligent “gateway” to our house.This central communications and control de- vice could help manage use of all the different power sources (utility power via an IUT, solar panel, batter- ies, plug-in hybrid electric vehicle) and match them to the load to optimize energy efficiency and comfort.This “Consumer Portal” as it is called by EPRI, could also be the central communications hub for the household, us- ing power lines to carry signals.

The DC-powered home pictured in Figure 20 is still a fantasy. How- ever, technologies are within reach to make it both possible and practical. Changing product designs to eliminate conversion of AC to DC power for electronics and VFDs, and emerging technolo- gies such as plug-in hybrid electric vehicles, the Intelligent Universal Transformer (IUT), and the Consumer Portal could make this pic- ture a reality.

The convergence of technologies may enable us to take generators to where we use electricity—and allow us to seamlessly integrate dispersed generation and renewable resources with the central generation backbone of our electric power system.A DC-powered home could become a component of a network that increases the security, quality, reliability, and affordability of the electric power system. Technology can allow this to happen—your “House of To- morrow” may indeed be a DC house. Or at least a “House of To- morrow” where low-voltage AC and DC wiring both are present.

For more information on the Intelligent Universal Trans- former, plug-in hybrid vehicles, and the Consumer Portal, visit www.epri.com.

June 2006

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