Google and IEEE announced today that Belgium's Red Electrical Devils, a team from CE+T Power, has won the Little Box Challenge, a competition to invent a much smaller inverter for interconnecting solar power systems to the power grid. The success earned the team a $1 million prize while proving that inverters can be the size of a tablet or smaller rather than the size of a picnic cooler, more than a factor of 10 reduction in size. The Energy Department's National Renewable Energy Laboratory (NREL) provided critical analysis of the 18 finalists teams' inverters to help determine the winner.
On Oct. 21, 2015, each of the finalists brought their inverters to the Energy Systems Integration Facility (ESIF) on the NREL campus in Golden, Colorado, for testing. "The overall idea was to test these inverters in a similar fashion to how they would be used out in the field," said Blake Lundstrom, the NREL project lead.
The first step was to verify that the inverters met all critical safety-related specifications and then to simply turn the inverters on and see if they functioned. Next, was a three-hour procedure to operate the inverters at a number of different operating points and to verify that key specifications were met throughout the three hours. After these challenges, the field of eighteen finalists was narrowed to the remaining inverters that would proceed to the third round.
Those final inverters were subjected to a 100-hour simulation of real-life conditions, including a direct-current source of electricity that emulated a solar power system, with rapid ramp-ups and ramp-downs in power typical of an intermittently cloudy day, as well as a realistic, changing load typical of a residence that the inverter needed to supply. Each inverter had to meet most of the same specifications required of commercially-available inverters.
"We were checking that all the specifications were met, under realistic conditions that a similar solar inverter in the field would experience, and evaluating their thermal performance over the long term-those are the key things that we were looking for over those 100 hours," said Lundstrom.
The teams also presented the highlights of their designs and lessons learned from the design process to a team of researchers and engineers from Google, IEEE, NREL, and others in the power electronics industry.
Teams from Schneider Electric and the Virginia Tech Future Energy Electronics Center won honorable mentions. The winners were announced at the ARPA-E Energy Innovation Summit in Washington, D.C., which aims to move transformational energy technologies out of the lab and into the market.
The Red Electrical Devils were declared the winner by a consensus of judges from Google, the IEEE Power Electronics Society, and NREL. Their inverter had a power density of 143 W/in3-far greater than the minimum requirement of 50 W/in3 and 50% higher than the nearest competitor-and a volume of only 14 cubic inches, smaller in volume than a cube measuring 2.5 inches on each side. The winning inverter also performed better on measurements of electromagnetic compliance (the amount of electrical noise emitted from the unit).
Shrinking inverters by an order of magnitude and making them cheaper to produce and install will enable more solar-powered homes and more efficient distribution grids, while helping bring electricity to remote areas. A key factor in the winning inverters was the use of wide bandgap semiconductors, a technology that enables power electronics to operate at higher voltages and temperatures, allowing them to transmit more energy through a smaller volume.
"Wide bandgaps offer a lot of advantages over traditional silicon that enabled teams to hit some of the miniaturization and efficiency targets that were needed to be successful in the competition," said Lundstrom. "Not every single team used wide-bandgap devices, but the vast majority did."
Leading teams were also innovative in their cooling designs and packaging techniques, including efficient integration of their designs onto printed circuit boards, said Lundstrom.
"The Little Box Challenge actually forced people to try to optimize space, and a nice outcome of that is that some of the techniques to do that are going to be pretty helpful for other aspects of inverter development," said Lundstrom. "For example, once you have a device that is almost entirely integrated onto a printed circuit board, it's easier to manufacture. Plus, some of the teams were able to incorporate all this innovation without adding any additional cost to the inverter and in some cases these designs may result in reduced inverter cost when mass-produced."
ESIF is the newest Energy Department user facility and the only one in the nation focused on integration of clean energy resources into the electric grid at utility scale. At ESIF, NREL offers industry partners access to award-winning, state-of-the art lab space, and a team of specialized scientists and engineers who provide advanced capabilities for research, development, and demonstration of key components of future energy systems.
NREL's contribution was supported, in part, by funding from the Energy Department's Office of Energy Efficiency and Renewable Energy in support of its SunShot Initiative. The SunShot Initiative is a collaborative national effort that aggressively drives innovation to make solar energy fully cost-competitive with traditional energy sources before the end of the decade. Through SunShot, the department supports efforts by private companies, universities, and national laboratories to drive down the cost of solar electricity to $0.06 per kilowatt-hour. Learn more at energy.gov/sunshot.
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NREL is the U.S. Department of Energy's primary national laboratory for renewable energy and energy efficiency research and development. NREL is operated for the Energy Department by The Alliance for Sustainable Energy, LLC.
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