How and where does low voltage direct current fit into the sustainability puzzle

Issue 29 – July 2011

This article is summarised from Electroindustry magazine Vol. 16 No. 6 by permission of the National Electrical Manufacturers Association.

What do photovoltaic systems, LEDs, computer power supplies, and digital data centres have in common? All use or generate low voltage direct current (dc). Applications and sources of this alternative technology are expanding. This is a change from the alternating current (ac) that has been powering the digital age. But what's driving this new energy? Does its use fit with the goals of sustainable energy? Where will this resurrected method be in 5 years? 10? Right now, dc powers everything from small digital personal devices to electric vehicles and buildings that house rows of computer servers. Why is the power that Edison 'built' coming back after decades of dominance by Westinghouse's ac?

National Electrical Manufacturers Association (NEMA), Underwriters Laboratories (UL), and National Fire Protection Association (NFPA) sponsored a workshop in April 2011 near Washington, DC, to examine sources, distribution, and applications of low voltage direct current (LVDC). Over 140 attendees heard from industry, government, and utility representatives about the latest developments in achieving higher efficiency and improved reliability for dc systems. Speakers from the nation's stakeholders focussed on where this growing industry is getting its 'power,' what is driving the resurgent interest, and where it may be headed.

In opening remarks, Jack Wells, Pass & Seymour/Legrand Vice President of Corporate Development, said that it appears that the great Westinghouse/Edison battle over ac versus dc is coming full circle. Edison's preference for dc lost and ac became our primary distribution and utilisation current, largely because of dc's inability to be efficiently distributed over long distances.

Today, as we search for new methods to achieve sustainability and convert to renewable energy sources, technologies are developing to generate and store electricity locally. These include solar photovoltaic systems, fuel cells, storage technology, and electric vehicles. Wells paraphrased Donald Rumsfeld. 'There are things we don't know we don't know,' says Wells. 'Our challenge today is to try to identify some of the unknown unknowns.'

Dennis Symanski, Senior Project Manager at Electric Power Research Institute, explained how LVDC fits into Smart Grid and the overall electrical system, and highlighted key applications. These include data centre power, supply power for major residential appliances, rapid charging for electric vehicles, efficient lighting, and powering consumer electronics without the ubiquitous 'black brick.' Challenges for this LVDC Smart Grid initiative will include standardising a set of dc voltages, establishing a set of appropriate Standards to facilitate interoperability, changing the way building power is installed, and expanding the vendor sources for the devices that will be the building blocks for LVDC systems.

Energy storage

Maintaining a level supply of power from renewable distributed energy sources when there is no sun or wind will have to come from storage systems that charge up when excess power is generated and slowly release it when utility-supplied power is too expensive or insufficient.

Kevin Lynn, Acting Lead for Systems Integration of Solar Energy Technologies at the U.S Department of Energy, spoke about the integration of photovoltaic systems into this new energy system.

Walter Culver, PhD, Board Chairman of the Great Lakes Energy Institute at Case Western Reserve University examined a cost benefit analysis of the energy storage component that will be critical to the success of LVDC.

Emeka Okafor spotlighted his company – American Electric Power – as an example of researching new storage technologies and testing them in practical applications, while Christopher Kuhl spoke about the related topic of intelligent distributed energy storage, using SBB Energy Corporation's activities to clarify the concept.

David Geary, Vice President of Engineering for Direct Power Technologies, drew on his experience with developing alternative energy solutions to describe the use and rationale for 380 V dc applied to data centres and other high technology facilities. Reducing the current requirement for powering electronics by increasing voltage achieves an improved efficiency by lowering heat generation and the cooling load for buildings.

Enabling dc grid applications

Brian Patterson, Chairman of the EMerge Alliance, concentrated on the application of a grid system to provide efficient power to space lighting and other applications. By enabling the direct connection of low voltage dc lights to a novel ceiling-based electrical infrastructure, efficiencies are realised through the elimination of multiple power conversion devices, each of which experiences energy loss in the process of that conversion. Patterson also highlighted the concepts of net-zero energy buildings, hybrid dc microgrids in buildings, and the premise for the Enernet, what he calls 'the internet of powered things.'

Alan Manche, Director of Industry Standards for Schneider Electric, addressed many of the issues involved in enabling LVDC to be transported from generation sources to the growing number of applications. These applications will include electric shock protection devices, overvoltage protection, and protection against excessive currents that can cause overheating when faults occur.

Dr Fred C. Lee, Director at the Centre for Power Electronics Systems (CPES) at Virginia Tech, introduced the concept of nanogrids, where individual houses can become a system with generation, distribution, and utilisation of LVDC. Through this concept, being tested at the CPES, a house, groups of houses, individual buildings, or other units can become essentially independent electrical systems, removing some of the power burden from the national electrical grid.

A research scientist with Intel Labs, Guy AlLee, presented information on the move from central computing and central power generation to personal computing and nearly personal power generation. Part of the focus on this movement is to increase the availability of energy from renewable sources and for underserved markets. It could also enable a significant influx of high technology in areas in which the routing of utility power has not taken place.

Michael Stelts, Panasonic Director of the U.S. Standardisation and Collaboration Center, addressed the migration from ac to dc power for home entertainment products and how LVDC systems will improve economy of use and integrate them into electrical systems in the homes of the future.

Tim Mellon, Director of Government Affairs for SAE International, brought the workshop attendees up to date on the developments in the electric vehicle (EV) field. He noted the achievement of a standardised plug and considered how the EV as a source and load will fit into the electrical system.


Wim de Kesel, Group Vice President for Standardisation at Legrand, briefed attendees about the International Electrotechnical Commission (IEC) and its activities in the area of LVDC. He noted the high level of interest, including the assignment of a strategic group reporting to the Standardisation Management Board of the IEC to coordinate work in addressing the standardisation needs for LVDC systems and products.

Ken Gettman, Director of International Standards at NEMA, presented the U.S. efforts to lead and participate in the LVDC work occurring in the IEC. NFPA Chief Electrical Engineer Mark Earley spoke about the National Electrical Code® (NEC), which provides requirements for electrical installations throughout the US and other countries. He highlighted how aspects of LVDC are already included in the body of the NEC and how efforts are being initiated to address any deficiencies in this area.

Ken Boyce, Principal Engineer Manager – Energy at UL, emphasised the need to develop Standards addressing generation, storage, distribution, and use for LVDC to 'address key issues such as safety, interconnection, and interoperability.'

International Association of Electrical Inspectors CEO and Executive Director David Clements discussed how to engage the local authorities responsible for ensuring building safety. He encouraged collaboration among manufacturers, building owners, and inspectors to facilitate safe installations by using inspectors' knowledge and code understanding.

The workshop was filled with positive attitudes and the promise of continued advancements in the use of LVDC. NEMA will be hosting a web-based discussion forum to enable continued exchange of information and ideas. For more information please email Ken Gettman, Director of International Standards at NEMA,

Published in energy.