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An EPRI White Paper

DC Power Production, Delivery and Utilization

Potential Future Work and Research

the kitchen countertop shown in Figure 19, can charge a host of portable appliances.

In fact, equipment throughout the entire house could be pow- ered by DC, as shown in Figure 20.

ers will alter their products and add DC power ports—or make other changes to their equipment. To document potential and expand markets, additional demonstrations are needed with equipment that holds promise for use with DC power delivery, such as variable frequency drives.

Technology advances suggest that there are significant op- portunities for certain DC-based applications, and promising benefits in terms of energy savings and increased reliability. But many obstacles must be overcome. Additional research, development and demonstration are needed to make DC sys- tems viable. Below, we discuss some of the barriers and re- search needs presented by DC power delivery systems.

The business case for DC power delivery is not yet clear.

Will potential operating cost savings be sufficient to warrant initial capital investment for early adopters? For what appli- cations? To what extent will DC play into new power delivery infrastructure investments? How, for example, can DC power systems enable use of plug-in hybrid vehicles, which may be- come tomorrow’s mobile “mini” power plants? Systems that will accommodate efficient, safe, and reliable power delivery between such vehicles and either energy sources or loads are needed. Whether DC power systems are a practical option must be assessed.

Most equipment is not yet plug ready; demonstrations with

manufacturers are called for.

Even though electronic devices ultimately operate on DC, they have been designed with internal conversion systems to change AC to DC, and do not typically have ports for DC power deliv- ery. Although some specific products are available to accept DC power—such as DC fluorescent lighting ballasts, or server rack distribution systems—for most loads, AC 60-Hz power still must be supplied. Since the electronics market is highly competitive and has relatively low profit margins, a compelling business case is necessary before product designers and manufactur-

For data center applications, more field testing and perfor- mance measurement are required.

Several manufacturers have developed components that en- able DC power delivery in data centers, including rectifiers, storage systems, DC to DC converters, and rack distribution systems. However, the benefits of DC power delivery, such as energy efficiency, have only been estimated, based on vendor claims and rated performance of various components. Mea- sured data on potential energy savings, as well as other perfor- mance metrics such as power reliability and power quality, the lifetime of converters, maintenance needs, and other factors are required.

Safety and protection standards and equipment need to be developed.

Since DC power does not cycle to a current “zero” 120 times per second like 60 Hz AC current does, it is more difficult to interrupt the flow of DC power. Therefore, DC power switches and interrupters employing semiconductors or other technol- ogy are needed for DC delivery systems. Also to be addressed are when and where solid state switches need to be applied, and when an air gap is required. Further, techniques for con- trolling transients, such as spikes from lightning strikes, re- quire additional investigation and testing—as does research for grounding and balancing DC.

Standard practices for design, installation, and maintenance need to be established in the marketplace.

Adoption of any new technology or design procedures can represent a significant hurdle. Designers, technicians, install-

June 2006

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