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Solar Decathlon solar house competition heats up

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October 12, 2009

Students from the Cornell Hotel School cook in their “Silo House” for members of competing...

Students from the Cornell Hotel School cook in their “Silo House” for members of competing teams (Photo: Stefano Paltera/U.S. Department of Energy Solar Decathlon)

Competition is underway in the Department of Energy's (DoE) Solar Decathlon, in which 20 teams of college and university students compete to design, build, and operate the most attractive, effective, and energy-efficient solar-powered house. The house designs entered in the competition not only capture heat and light from the sun, but also integrate design features to take advantage of cooling breezes and shading. By combining these proven energy efficient designs with the latest off-the-shelf technology, the teams aim to create homes that reduce utility bills and meet all their energy needs, while providing all the comforts of home.

Water wall

Among the innovative designs on show is the University of Arizona's (UA) Project Sage house, featuring a water-filled Trombe wall that forms a solar thermal collector. The principle of the wall is that a piece of glazing is put over something with high density, so that when sunlight comes through the glass and the radiant heat is absorbed by the mass, it warms the air between the glass and the wall. At nighttime, when the temperature drops, the heat can't get back out through the glass and the warm air rises in the cavity and can be directed into the house through louvers in winter, or vented outside in summer.

The walls are made from vacuum-sealed panels constructed from the same material as recyclable plastic water bottles. It contains football-shaped cavities that are filled with water. In total the system holds 215 gallons of water (just over 2,000 pounds) and every cubic foot of water can hold 64 Btu's for every degree Fahrenheit of temperature change. This makes the system three times more efficient than concrete and it's also much lighter to ship because the water can be added at its destination. Plus, the team says living next to a water wall provide, "some really neat optical effects and lighting effects."

The wall is the brainchild of Eddie Hall, who cautions that, like many things in the experimental house, it is a prototype, but it has been refined after a year and a half of experimentation.

Living in a Silo

In contrast to some of the more traditional looking designs on display, Cornell University's "Silo House" stands out with a trio of interconnected rust-colored cylinders positioned under floating solar panels. The cylinders house three interconnecting cylindrical rooms, which sit around a square courtyard shaded by the photovoltaic (PV) panels above. Each silo is 16 ft (4.9 m) in diameter, with about 130 ft2 (12.1 m2) of floor space and serves a different function - kitchen, bedroom and living room.

The modules are joined on the southern side, but the northern side is left open. The exterior is covered with Cor-Ten, a corrugated, steel cladding whose outer layer oxidizes to a weather-proof rusty coating that gives the Silo House its distinctive coloring. Solar heat absorbed by the Cor-Ten steel siding on the southwest side of the house is transferred to fluid running through copper pipes hidden underneath the corrugated steel skin. This preheats water entering the domestic hot water tank before the primary heating is done by an Apricus evacuated tube solar thermal system.

Acting together, these systems allow 15 gallons of hot water to be supplied to the showers in ten minutes with the 120-gallon tank able to store heat for days without sun. If the heating mechanism doesn't provide enough hot water, a backup electric resistance heater in the how water tank can finish the job.

Photovoltaic panels on the move

Unsurprisingly, PV cells play a big part in all the house designs entered in the 2009 Solar Decathlon and a couple of entries have come up with ways to maximize the energy captured by their respective rooftop arrays.

Virginia Tech's Lumenhaus sports a single array of bifacial panels that capture energy on both sides to increase energy output by 15 percent. Using an electric actuator, the entire PV array can be tilted to the optimal angle for each season (from zero degrees to a 17-degree angle in summer and to a 35-degree angle in winter), to allow for maximum solar energy collection.

Even more impressive in its sun following capabilities though, is the Black & White House from Spain's Universidad Politécnica de Madrid (UPM) with a self-orienting solar roof. The solar roof pivots on a single point, courtesy of a ball-and-socket joint, which enables it to capture the maximum solar energy throughout the day, anywhere in the world, by having the roof follow the path of the sun.

And it's not just the roof that features PV cells to capture energy from the sun - each façade of the Black and White House is clad with photovoltaic modules. These glass-glass photovoltaic modules have Polycrystalline Silicon cells that allow 45 percent of the light to pass through, thereby optimizing the capture of solar energy and also creating shade protection for the interior spaces. They are positioned at the corners of the house, pivoting on the corner point to follow the sun throughout the day and again maximize solar energy capture.

Although the team must currently manipulate the PV panels manually, they say that in the future the panels would be automated to achieve constant self-orientation of both the roof and façades.

Just to name a few

We've only taken a brief look at some of the more innovative designs the Solar Decathlon entries have thrown up, since a detailed examination of all the various technologies employed by the 20 entries would probably take nearly as long as the week long competition itself. One thing is for sure though - competition is definitely a healthy thing and looks like offering some real health benefits for the environment.

Anyone looking for a more in depth examination of all the entries can check out the Solar Decathlon website or, if you're in the neighborhood, get along to the competition site located at the National Mall in Washington, D.C., which is open for public tours. The houses are open to the public until October 13 and will be closed for competition monitoring on October 14, before reopening to the public from October 15 to 18.

About the Author
Darren Quick Darren's love of technology started in primary school with a Nintendo Game & Watch Donkey Kong (still functioning) and a Commodore VIC 20 computer (not still functioning). In high school he upgraded to a 286 PC, and he's been following Moore's law ever since. This love of technology continued through a number of university courses and crappy jobs until 2008, when his interests found a home at Gizmag.   All articles by Darren Quick
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