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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?

Will the “House of Tomorrow” feature DC low-voltage wiring? In- stead of relying on the standard AC system with 120V outlets for general use or 240V power for larger loads like air conditioners or ovens, will DC wiring become standard? And will it enable greater efficiency and convenience? Some believe it can and offer argu- ments that the DC-powered house (or at least a hybrid DC/AC house) can be a future reality.

Consider the electronic equipment and devices in a typical home— in how many places are there inefficient AC-DC conversions?

To charge your iPod, personal digital assistants (PDA), cell phone, or the myriad other items that run on DC power, you may have 9V or 12V outlets.The cell phone’s microprocessor needs only single-digit DC voltage, so wouldn’t it make sense to get it from a DC outlet?

But before getting too carried away with electronics,remember that the bulk of your electricity bill is not for running your computer. “Energy hogs” in the household such as the air conditioner, heat pump, refrigerator and other motor-operated equipment, account for the greatest share of energy consumption. And these motors run on AC.

Instead of plugging in your computer at a 120V AC outlet you could plug it in directly to, say, a 48V DC outlet, thus reducing the need for an AC to DC conversion in the computer.

Are motors a stumbling block for DC power? Not necessarily. In fact, motors could be the ideal load to power with DC. The rea- son is a revolution in use of motor speed control using electron- ic variable frequency drives (VFDs). VFDs operate by converting

Figure 22.

AC source

DC source

120 / 240 V AC

170 / 340 V DC




Adjustable speed drive

Current configuration

Tomorrow’s configuration

The voltage shown here might be 48 V instead. Either 48 V and/or 170/340 V DC could be used.The right DC voltage is a question that is still being addressed by researchers.

June 2006

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