The future of energy efficiency may be more than saving energy. It may also be efficient energy capture, storage and delivery. Technologists, engineers and some forward-thinking manufacturers are working to set a bigger table for direct current (DC), and one effort may be all-encompassing. It’s called DC-to-DC power.
The EMerge Alliance, a nonprofit industry coalition headquartered in San Ramon, Calif., wants DC to play a greater role in an alternating current (AC) world. It and other advocates see DC providing deeper adoption of alternative energy, power storage, a smarter grid and a world of microprocessed electronics.
“AC has been the format for 100 years, principally based on its good match with fixed-frequency, coil-wound motors and transformers [as well as] incandescent and magnetic-ballasted fluorescent lighting,” said Brian Patterson, EMerge president. “But is it the best or only choice in a world of increasing solid-state devices and other electronics?”
As examples best served by DC, Patterson cites electronically ballasted fluorescent, light-emitting diode (LED) lighting and controls, variable-frequency AC, and electronically commutated brushless DC motors used in appliances and industrial automation.
“In fact, our use of electricity is rapidly switching to solid-state electronics and actuators that natively run on DC,” he said.
EMerge has developed its Occupied Space Standard Version 1.1 and its Data/Telecom Center Standard. The Institute of Electrical and Electronics Engineers (IEEE) is exploring the adoption of these standards that serve as an open power-distribution platform for the use of safe, low-voltage DC power.
“We simply ask, ‘Why do double—or more—the conversions from DC to AC to DC?’” Patterson said. “The inherent inefficiency of low-current, low-voltage conversions waste power from the single digits to as high as 20 percent, depending on equipment and setup.”
Patterson also said AC 60-hertz (Hz) power significantly complicates source integration (synchronization) and phase control in a digitally controlled world, while DC (commonly 24V) simplifies.
“At this level [24V] the power is touch-safe, so you use exposed busses and eliminate ground wires,” he said. “The wiring is also less expensive and easier to install. DC systems also better accommodate digital electronics. Like we are seeing in lighting, we’d like to see the electrical world go digital.”
Even so, Patterson said AC power has its place.
“With relatively few modifications, traditional AC bulk power [the grid] will continue as a key electricity production and transmission resource,” he said. “Technologies like induction cooking and wireless power charging that use AC [albeit not fixed 60 Hz] will also be important. We need both AC and DC electricity but in the right form for the right job and in the right place.”
Right form, right job and right place influenced how DC/DC factored into the development of a product that served as the germination of the EMerge Alliance and its standards.
“Skidmore, Owings & Merrill LLP [SOM], Philips Lighting and Armstrong World Industries had an idea,” Patterson said. “SOM was saying to Philips, ‘You’re developing LEDs as a broader based lighting source. And, Armstrong, you are doing innovative things with ceilings and other interior architecture. What if we bring them together in an innovative, smart way that delivers lighting and energy dividends?’”
That led to discussion with Nextek Power Systems, Detroit, which designed the new product to run with DC and solar energy. The first standard for “Occupied Space” was modeled after the collective work on the solar-LED-ceiling concept. The resulting product and first EMerge certification was Armstrong’s DC FlexZone, a DC-powered ceiling-suspension-grid system offering plug-and-play flexibility for LED lighting, controls and other building operations. DC main beams run through the grid-ceiling system. Twelve major lighting and controls manufacturers have products compatible with FlexZone.
Today, EMerge is also working on whole-building/campus energy use in nonlighting systems such as data centers/IT; heating, ventilating and air conditioning (HVAC)/air handling; plug loads; desktop IT; and other power consumers.
A DC/DC focus
Nextek’s office is located in the Next Energy Center, called “a living laboratory for advanced energy and transportation technology development.” Working with the center, Nextek helped create the NextHome living lab, which allows companies to develop and commercialize DC technologies. The lab is equipped with Nextek’s Direct Coupling power distribution platform for DC power. The DC modular home features appliances, fast-charging (Level 3) electric vehicle charging stations, energy storage, lighting and photovoltaic HVAC.
In another DC-to-DC project, Nextek had great success without incorporating green energy or storage.
“Our work on an office building for the state of Michigan in Flint consisted of a wireless, low-voltage mesh network featuring 1,200 nodes that provide control for the entire 100,000-square-foot building,” said Paul Savage, Nextek CEO. “This project is all direct current without on-site solar or batteries.”
Savage said his firm works to achieve a 10–42 percent energy savings on all of its DC-to-DC projects.
EMerge has more than 100 organizations, including universities and national labs (e.g., Lawrence Berkeley National Labs), assisting in research and development. Lawrence Berkeley’s interest in DC-to-DC has led to a collaboration with the Electrical Training Institute.
“Berkeley Labs received a DC-to-DC grant,” said Brent Moss, training director for the Electrical Training Institute, a joint venture of the International Brotherhood of Electrical Workers Local No. 11 and Los Angeles County Chapter of the National Electrical Contractors Association. “We are now partnering with them using our the Net Zero Plus Electrical Training Institute as a setting for what DC-to-DC power could provide in terms of additional energy efficiency. Right now the project is in the talking-and-planning phase.”
Moss described how five of the training center’s classrooms would be retrofitted for DC power.
“We want to find how DC-to-DC pencils out as we use it for our LED lighting and other straight DC loads, including classroom computers, audiovisual and projection systems,” he said. “We would draw from the solar inverter as our solar panels already produce DC energy. The inverter will smooth and condition the power. We would compare against five classrooms operating on AC.
“DC-to-DC is certainly evolving. If the industry moves this way, we should be prepared. On the energy side, it’s another way to do more with less,” Moss said.
Other DC explorers
EMerge has worked to network with national organizations such as the U.S. Green Building Council and local ones like the Alliance for Sustainable Colorado. Sustainable Colorado is interested in transforming its 40,000-square-foot Alliance Center into its own solar-powered DC microgrid. The effort has been named the “dcProject.”
The center underwent a major redesign two years ago in an effort to make the office building as energy efficient as possible. Its energy use intensity was reduced from 89 kBtu per sq. ft. per year to 37 kBtu per sq. ft. per year using passive lighting and other tactics before adding alternative energy and storage. Sustainable Colorado’s founder, John Powers, advanced the idea of adding DC-to-DC power.
“We’re now experimenting with what energy reduction we can gain through DC power based on where can presently apply it,” said Mark Reiner of Non Sequitur, a consultant for the Alliance. “We’ve increased efficiency with our solid-state, electronic-based operation in much of our equipment, eliminating a 7 percent energy loss at each point they would normally be fed AC power. This helps as we attempt to create a local distribution of power within the building.”
“Our DC power is first delivered from a battery bank of solar-power storage,” said Sandy Vanderstoep, special projects director, Alliance for Sustainable Colorado. “We also still connect to the AC power grid, but optimized our power through this hybrid approach. DC-to-DC loads we can tackle today include heating and air conditioning demand, lighting and plug loads.”
Other efforts to improve building performance include high levels of daylighting and energy-management controls working with occupancy sensors.
“We don’t view ourselves so much as a demo project but a laboratory for DC-to-DC,” Vanderstoep said. “The dcProject is proof of feasibility. Instead of projecting energy saving, we are measuring. Our goal is to establish that DC-to-DC really works but with refinement.”
The dcProject is expected to switch more mechanicals to DC-to-DC over the next two years. Increasing the amount solar power for a viable solar/DC microgrid is also at work. Vertical PV panel arrays have been installed to the building’s exterior walls. Photovoltaic cabling is also being used.
Also, the alliance is investigating the performance of used storage batteries, which are cheaper to purchase. The building’s current 60-kilowatt battery storage unit uses advanced lithium-ion. Other batteries being tested include nickel-metal hydride, aqueous hybrid ion and super-charge ion.
In the end, market adoption of DC-to-DC will need public policy affirmation to take off.
“A DC-to-DC market seems ridiculous until it’s ubiquitous,” Savage said. “It’s a cross-cutting technology that can also play in the electrical generation and delivery industry. We need to build support at the federal, state and local levels. Large developers are coming to the NextHome to see what it is, what’s there and who’s involved. That’s encouraging. It will take someone with the big order to take this concept to the next level in marketability and exposure.”
Savage is encouraged by finding DC-to-DC referenced as an energy tactic within the U.S. Department of Energy’s quad-rennial report. He also emphasized IEEE’s consideration of EMerge standards is a major milestone for the DC-to-DC movement. For its part, Sustainable Colorado has won local and state code backing for its use of DC and solar-energy storage in its building renovation.