We are at the inflection point of a new revolution: DC-power infrastructure is set to replace AC-infrastructure in many, if not most, commercial buildings. The case is simple: Almost every device in a modern building uses direct-current (DC), including LED lighting, sensors, variable speed motors, pumps, and so forth. As we move towards greater numbers of net-zero energy buildings, both onsite solar PV and battery storage are intrinsically DC-based. And all digital devices are DC – local data centers and IT infrastructure, plus with the high wattage capacity and rapid adoption of USB-C, all our digital devices will consume power through a standardized DC format.
The big picture is that we can realize 10-15% reductions in power consumption by skipping DC-AC-DC conversions.
Plus, beyond the core energy savings, there are many secondary benefits of migrating to DC-infrastructure: Less equipment, lower cost through simpler architectures, and DC fundamentally marries to digital IoT tech easier than AC, making it easier to build more sophisticated controls and analysis software packages on top.
“BUT WAIT!” you say….”HASN’T THE EMERGE ALLIANCE BEEN TOUTING DC FOR YEARS, TO NO AVAIL???”
Yes, it has (and it has great library of technical resources that you should dig into) and certainly, uptake of DC has been slow. The difference now is that solar PV and battery storage have plummeted in price so much, and continue to do so, that it is becoming cheaper to generate electricity at your building site than to buy it from your coal-belching utility operator. Suddenly, using DC-infrastructure to gain an extra 10-15% efficiency of your onsite power generation and storage makes a compelling ROI story.
Don’t believe the core energy savings? Let’s review three research papers that studied the potential efficiencies:
A detailed paper from the Imperial College of London, sponsored by the Engineering and Physical Sciences Research Council concludes the following:
In particular, the case, where energy is deduced entirely from distributed energy resources (DERs) and new-technology efficient appliances are used, shows to be very promising. In fact, from the efficiency analysis, if we replace AC with DC we will potentially save about 13% of electrical energy consumed in offices in the last years. This figure is only representative of the bare replacement of AC with DC, because other savings derive from the replacement of old appliances with new ones that are naturally DC-suited.Comparison of cost and efficiency of DC versus AC in office buildings, Giuseppe A. Laudani, PhD &
Paul D. Mitcheson, Imperial College London
There is an ongoing U.S. DOE research project titled Direct Current (DC) Buildings and Smart Grid, operated out of Lawrence Berkeley National Laboratory. A summary slide deck can be found here. The first half of the project was a detailed simulation of an office application, which concluded:
…using DC distribution can be considerably more efﬁcient: a medium sized ofﬁce building using DC distribution has an expected baseline of 12% savings, but may also save up to 18%. In these results, the baseline simulation parameters are for a zero net energy (ZNE) building that can island as a microgrid. DC is most advantageous in buildings with large solar capacity, large battery capacity, and high voltage distributionA simulation-based efﬁciency comparison of AC and DC power distribution networks in commercial buildings, Daniel L. Gerber, Vagelis Vossos, Wei Feng, Chris Marnay, Bruce Nordman, Richard Brown
NREL, another US DOE lab, conducted a research project several years ago with Bosch demonstrating the efficiency of DC microgrids. Their introduction:
By transitioning most of the major hard-wired loads in a building to the DC distribution system, customers can expect up to 30% lower total cost of ownership over the life of the system, higher reliability, and optimized use of renewable generation compared to a conventional AC microgrid. At scale, the capital cost is anticipated at 15%–20% lower than a comparable AC system; the operating costs will also be
significantly lower over the 25-year life of the system. The DC system architecture is applicable to a wide variety of commercial buildings, including big-box retail stores, warehouses, distribution centers, and manufacturing facilities.
For a project that used solar PV, lighting and a grid connection (no battery storage), they concluded:
NREL’s simulation study of the DC microgrid concluded that it improves the percentage of PV energy that performs useful work to approximately 97% from a baseline value of 90%, with small variations in response to design parameters, operating conditions, and locationA Comparative Study of DC and AC Microgrids in Commercial Buildings Across Different Climates and Operating Profiles, Daniel Fregosi, Stephen Frank, et al,
The big players like ABB, Bosch, Schneider, etc. know this trend is happening. But they don’t want it to, as all their sunk capital costs are in AC infrastructure (and lately, with complex digital tech slathered on top of old AC tech). They don’t want to have to spend the money developing and launching a fundamental new product line. Small startups like LumaNEXT will be the disruptive pioneers in this next wave of transformation.