It’s been more than a century since alternating current (AC) won the battle against direct current (DC) as the technology of choice for distributing electricity across the grid and in buildings. But maybe it’s time to rethink that choice, and convert homes and businesses to DC power for more efficient use of the increasing portion of electricity consumption and generation that runs on direct current.
That’s the idea behind a U.K. Department of Energy and Climate Change project announced last month, aiming to integrate solar power, batteries and LED lighting and home electronics into a single DC-powered system. The goal is to reduce inefficiencies related to converting DC to AC and back again, and bring the control capabilities that come from a core DC power technology -- the USB cable -- to better manage household power loads for grid needs.
That’s how Simon Daniel, founder of U.K. startup Moixa Technology, describes the project’s goals. Moixa has developed DC-powered systems ranging from USB adapters to home energy control systems, and is leading a consortium including KiWi Power, Good Energy, AVC NextGen and Northern Power Grid on the DECC project, one of two awarded £5 million ($8.2 million) in grants last month.
About 300 homes will be equipped with Moixa’s Maslow home energy management system, coupled with batteries that store power from the grid, as well as from small-scale solar PV systems at a subset of homes, Daniel told me in an interview last month. That DC power, in turn, will supply LED lights in the buildings, as well as use USB to power an array of consumer electronics, he said.
Daniel described these as the “above the waist” loads in the home, to contrast them with the “below the waist” appliances, pumps and other systems that will continue to run on grid-supplied, AC power. But while household power demand for these below-the-waist devices isn’t growing that fast, “the stuff above the waist keeps going up exponentially, and nobody knows what it’s going to be like in 2020,” he said.
That’s a problem for utilities struggling to provide peak power to homes and businesses where digital devices make up the fastest-growing share of electricity usage. The U.S. Energy Information Administration (EIA) has projected that household energy use attributable to miscellaneous devices, much of it consumer electronics, is set to nearly double between 2005 and 2015, while most other classes of loads show little projected growth:
All told, using DC power from the battery to power LEDs and digital devices could improve the efficiency of those systems by roughly one-third, compared to the losses that come from converting that power from AC to DC, he said. Allowing solar PV's DC output to go directly to batteries or the home's DC loads could also improve efficiencies on that side, allowing smaller solar systems than would otherwise be practical, he said.
Beyond that, however, “by putting in a very small system,” with roughly 1 to 2 kilowatt-hours of storage matched to LED and electronics loads, “you can take 20 percent off the daytime consumption, and more or less halve the average peak,” he said. “That’s quite significant in a country where half the peak is driven by domestic.”
That’s where Moixa’s partners come into the picture. Good Energy, a U.K. retail energy provider that specializes in selling green and low-carbon energy contracts to customers, will be able to tap the homes’ batteries and solar systems to help meet its promises. KiWi Power, a U.K.-based demand response provider, can manage the homes’ power control capabilities to shift and shape lots of household power loads for grid needs.
AVC NextGen, a U.K. provider of home broadband and IP television services, will be testing the commercial prospects for deploying these DC power systems on a mass scale, Daniel added. The goal is to cover the costs of deploying the technology via a combination of efficiency gains, peak energy reductions and green power premiums, as well as offer competitive differentiation for retail providers in the U.K.’s highly competitive energy market.
Changing a century’s worth of technology development and regulations built around AC systems so that they can carry DC power within buildings won’t be easy, of course. But efforts are underway to create the standards to bring DC power into the mainstream.
In the United States, for instance, the EMerge Alliance, a U.S.-based consortium of lighting and electronics controls manufacturers and construction firms, has been pushing DC power for commercial lighting since 2008. It’s also been promoting standards for DC power in data centers, where technology providers like Validus (now owned by ABB) and data center owners like Facebook have been making some strides.
Last month, EMerge launched a new initiative to develop DC power standards for homes and small businesses, largely aimed at enabling “hybrid” systems that can simultaneously run DC and AC over typical household wiring.
“You’re going to be in a hybrid mode most of the time -- some AC and some DC,” EMerge Chairman Brian Patterson said. “When you’re figuring out how they’re all going to fit together, you have to figure out where all these hybrid interfaces are going to be in the network.”
As for how household electronics will fit into a DC-powered home, EMerge is looking forward to next year’s release of a new USB PD (power delivery) standard, which is meant to boost USB’s power capacity to 100 watts, ten times what’s possible today. That could enable direct DC power for a whole new set of consumer electronics, as long as the standard interfaces are there to power them.
Reducing the inefficiencies inherent in AC-to-DC conversion is “just the beginning of the story,” he said. “It’s more about how we manage that power. We want personal electronics to power down when we’re not using them, and wake up when we need them -- and that’s going to be electronic management.”