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Solar Decathlon team builds showcase in China

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By Jonathan Damery, ECE ILLINOIS
September 19, 2013

  • Twenty Illinois students, including five from ECE, built a showcase home for Solar Decathlon China, held last month in the city of Datong. It was the culmination of a two-year collaboration with students at Peking University in Beijing.
  • With 42 solar panels on the rooftop, power production exceeded the consumption requirements of the home, making it more than net-zero.
  • An automation system, designed by an ECE-led team of students, controlled and monitored household utilities on an iPad.
Hundreds of visitors lined up outside the house, waiting patiently, some of them beneath the shade of their brightly colored parasols. The house wasn’t palatial by any means, only large enough to accommodate a family of three, but it was both modular and solar, wired with energy-saving electronics. And like nineteen other houses nearby, it was constructed for the first-ever Solar Decathlon China, held in the city of Datong, during the first two weeks of August. 
 
Etho House: the main entrance is located in the alcove at center. Photo by Zak Helmick.
Etho House: the main entrance is located in the alcove at center. Photo by Zak Helmick.
Before the competition commenced, an orange and blue sign hung on one wall of the house. “Go Illini!” it read. And there, Illinois students were working alongside teammates from Peking University, who had jointly designed the structure during a two-year collaboration. More than sixty Illinois students had participated in the design, with sixteen from the ECE Department.
 
Throughout the two-year preparation, the students communicated with their Chinese teammates via email and Skype, and last summer, twelve Illinois students traveled to China to attend workshops where they met with their teammates face-to-face. Now twenty were on site, giving tours of the completed home. 
 
The line of visitors wound up the gradual entry ramp to an opening in the perforated zinc privacy wall, which covered the front façade. On the upper corner of the wall, the name of the house—Etho—had been subtly written. “The house was very well received by the public,” said Agriculture and Biological Engineering Professor Xinlei Wang, the team’s faculty advisor. 
 
The students ushered the visitors behind the wall, through a narrow corridor, to the side of the home where the main entry was located. The house was designed as a modern interpretation of the traditional homes found in and around Datong and Beijing, with a single roof surface, sloping towards the back, and a central courtyard. The students revamped the style, making it architecturally modern and net-zero (that is, it produces all of the energy it consumes, if not more). The traditional courtyard was enclosed with photovoltaic glass skylights that admitted natural light while simultaneously producing solar power. The sloping roofs were covered with forty-two solar panels. 
 
“The most satisfying moment was when the [photovoltaic] system actually started outputting energy,” said Savan Kadakiya, a recent electrical engineering graduate and the electrical systems sub-team lead. “It confirmed that our house would be net zero.” In fact, the power production exceeded the consumption requirements. 
 
Upon entering the home and gathering around the modern dining table in the central courtyard, one of the first things tour groups noticed was the unusual lighting system, which operated on direct current instead of the standard alternating current. The light fixture hanging over the table utilized LED bulbs. They were rectangular and lacked the standard screw-in attachment associated with incandescent bulbs. Instead, magnets adhered the lights, and they could be easily removed or slid around the fixture to adjust the lighting. 
 
The LED light fixture is controlled using an Illinois-designed automation system. PV skylight above. Photo by Guanxin He.
The LED light fixture is controlled using an Illinois-designed automation system. PV skylight above. Photo by Guanxin He.
A slight hand motion controlled the wireless, battery-less light switches mounted on the wall, and the students also demonstrated the automation system, designed by the Illinois team, which controlled and monitored the household utilities on an iPad. By moving a slider on the touchscreen, the LED lights could be dimmed and the color could be dramatically altered, transforming the interior into vibrant, technicolored space. 
 
“Our system was a lot more custom,” said Dan Murray, a computer engineering student and member of the automation sub-team. “Every other team that attempted an automation system… adapted an industrial system for residential use, which is a bit unreasonable for even the most serious home automation hobbyist.”
 
Water-flow sensors tracked faucet-specific water consumption throughout the house, and using the automation system, the students could compare the kitchen faucet, for example, to the shower or the washing machine. Price points could also be displayed on the iPad, indicating the expenses associated with each water or energy consuming unit: “How much does it cost to run the refrigerator for one week? Is that more or less than the weekly lighting expenses?” The system also monitored photovoltaic production, temperatures and humidity throughout the home, carbon dioxide levels, and the like. 
 
“We by far had the best automation and user interface,” said Anish Chivukula, a recent electrical engineering graduate and leader of the automation and controls sub-team. 
 
Inside the small but packed mechanical room, team members showcased their unique hot water tank. Pipes connected the tank to a portion of the rooftop solar array that utilized solar-thermal panels. “Solar panels are black and obviously make electricity, but they also get hot,” said Mike Wang, the Illinois engineering lead and graduate student in mechanical engineering. Glycol-filled pipes ran within these panels, absorbing the heat, and this heated fluid was then pumped through coiled tubing inside the water tank, creating hot water for domestic use. “It slightly increases the efficiency of the solar panels too,” he added.
 
The solar-thermal system was also integrated with the heating and air conditioning system. In the winter, heat is extracted from the hot water tank, and is pumped through the house as forced-air. In the summer, the system switches to an external cooling tower unit, which provides efficient evaporative cooling. Essentially, the configuration emulates an otherwise geothermal setup for a water-sourced heat pump, but with a much smaller, self-contained design for the sake of the competition.
 
The mechanical room also held an energy recovery ventilator to provide prescribed amounts of fresh air. In the winter, the system removes heat from circulating air before it is exhausted and uses it to preheat incoming cold air. The opposite occurs in the summer. The building design also incorporated several types of insulation, including phase change materials, which absorb and store heat, releasing it only when interior temperatures start to drop. Those reduce the fluctuating demands on the heating and air-conditioning system.
 
There were two bedrooms, one bathroom, and in the mixed-purpose living room, large triple-glazed windows looked out toward the back porch. The visitors could exit onto the porch through a sliding glass door. And there, looking up the rear-sloping roof, the photovoltaic system could be easily viewed.
 
Team members finish work on the rooftop photovoltaic system. Photo by Guanxin He.
Team members finish work on the rooftop photovoltaic system. Photo by Guanxin He.
The system was designed using microinverters, instead of one central power inverter. In situations of partial shading, this allowed the system to adjust more precisely, so that the maximum power was always attained. According to Kadakiya, these microinverters were one of the most innovative features. “Very few teams used it,” he said. “In addition, the microinverters were able to perform under the harsh weather conditions of Datong, China, such as heavy wind and rainfall.” 
 
On-site construction in Datong had taken place over a two-week period prior the opening ceremony on August 2. But in keeping with the modular layout of Etho, the framing and basic assembly had been completed beforehand on the campus of Peking University in Beijing, and it had then been shipped to the competition site, about four hours away. The move required seven tractor-trailers and three consecutive nights of packing. 
 
“We were packers and movers. We were crane guides…we were janitors. We did everything,” said Mike Wang.
 
As for the actual competition, juries of field-specific professionals evaluated the homes on ten categories, including engineering, energy balance, and architecture. Because Peking University had organized the competition, the Illinois-Peking team had been asked to build a showcase home, and was not officially judged in the competition. Overall, the competition, sponsored by the United States Department of Energy and China’s National Energy Administration, brought hundreds of students from thirty-five universities and thirteen countries. Financial support was provided by more than twenty industry and university sponsors, including the ECE Department.
 
On Friday evening, a week into the competition, after everything had wound down for the day, the team gathered around the sleek quartz countertops in the kitchen. It was suppertime. Ginger, scallions, chicken, and tofu came out of the refrigerator in the corner. The wok was heated, the rice noodles cooked, and, yes, all of the appliances and all of the lights were powered by the rooftop solar array. Students from both universities gathered in the central courtyard, as many as could fit at chairs around the dining room table, and they ate.
 
“I would often stop and remind myself how the group of people accompanying me took an empty piece of land and transformed it into such an awesome, livable space,” Eric Johnson, a recent computer science graduate and member of the automation sub-team, said of the meal. “It was probably the best tasting food I had in China.”

Editor's note: media inquiries should be directed to Brad Petersen, Director of Communications, at bradp@illinois.edu or (217) 244-6376.

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