Carnegie Mellon researchers examine economic feasibility of using DC circuits to power lights in commercial buildings

PITTSBURGH, USA: For more than a century, electric power has been produced and distributed using alternating current (AC) technology championed by George Westinghouse and Nikola Tesla.

Carnegie Mellon University researchers report that a competing direct current (DC) electrical power system, pioneered by Thomas A. Edison in the 1880s, may be the most economic way to power lights in commercial buildings, especially in buildings using solar photovoltaics (PV).

In a paper published in Energy Policy, CMU's Brinda Thomas, Ines L. Azevedo and M. Granger Morgan examined the economic feasibility of using dedicated DC circuits to operate lighting in commercial buildings. They considered several lighting technologies and scenarios where the electricity used to power lighting devices in a 48,000-square-foot building came from either a central DC power supply or traditional AC grid electricity.

"We found that if you used DC instead of AC and your building has fluorescent light, the cost is basically the same or slightly higher with DC," said Azevedo, executive director of CMU's Climate and Energy-Decision Making Center and an assistant professor in the Engineering and Public Policy Department (EPP).

But if light emitting diodes (LEDs) were installed instead of fluorescent lamps, CMU researchers found a savings of $24,000 per year using DC instead of AC. If the LEDs were powered with solar PV power augmented with grid electricity, even bigger savings of $5,000 per year could be gained by using DC instead of AC.

And as the cost of LEDs decreases, the savings from transitioning to DC coupled with light emitting diodes will increase, according to CMU researchers. By 2015, projections from the Department of Energy show use of LEDs in a 48,000-square-foot commercial building could see cost savings of $10,000 per year compared to fluorescent lamps. The researchers found that decreasing the capital and operating costs of using LEDs, especially when used with solar PV, are key factors to make a dedicated DC strategy worth considering.

"However, our research shows that current DC wiring still has higher installation charges because it is a relatively new technology," said Thomas, a Ph.D. student in CMU's Engineering and Public Policy Department from Pittsburgh, Pa.

Morgan, CMU University professor and head of EPP, also pointed out that further work is needed to better understand potential safety risks with DC distribution and to remove design, installation, permitting and regulatory barriers.