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The students from Universidad Politecnica de Madrid had one of the longest journeys to reach the Solar Decathlon competition in Washington, D.C., transporting their "Black and White" house 3,800 miles by truck and boat. But the logistics didn't deter the team from developing and building one of the competition's most talked-about technologies: a self-orienting solar roof that tracks the sun throughout the day.

By far the showpiece of the Team Spain house, the 11-kW roof sits on a central ball joint which, along with a series of cables, allows the roof to pivot with the sun for maximum collection efficiency throughout the day. According to the team, the tracking brings an additional 10.3% power versus a stationary setup. The solar tracking is fully automated, as is a safety mechanism that brings the roof to a horizontal position in a high-wind or power outage event.

Additional photovoltaic modules are positioned on walls around the house's exterior façade; the mobile walls can be manually oriented to the sun throughout the day, a feature the team says will one day also be automated.

"Our main concept was to maximize solar capacity through active systems ... but also maximize passive solar design," says Irene Garrido, an architecture student and the team's communications leader.

Indeed, behind the movable exterior solar facades is a building envelope of double walls made of windows and doors that create a passive greenhouse for interior temperature regulation: during winter days, not only does radiant heat enter the interior of the home, but warmth created within the greenhouse radiates in during the night by opening internal doors; in summer, the large, commercial Kommerling windows and doors open for ventilation in the morning and evening, then close, along with blinds, during the afternoon.

Along the perimeter of the roof and within part of the "greenhouse" resides the dwelling's solar thermal system.

Beyond technology, the interior was designed to promote the livability of compact minimalism. "We wanted to show this could be a fine arrangement for two people," said one student of the home's multipurpose living space. With white walls and plenty of light from the windows and skylight, the interior has an open feel.

Rather than having a bedroom separate from the main living area, which includes seating areas and office space, the students incorporated a Murphy bed hidden behind the single room's rolling entertainment cabinet, which also contains a wardrobe and drawers. The remainder of the furniture also was designed with efficiency in mind: A cube unfolds into a dining table; an additional box within the cube houses four folding chairs.

The kitchen, which includes a refrigerator and washer by Miele and a Siemens dryer, dishwasher, and range hood, is separated in the northwest corner; the bath is cordoned off in the northeast corner.

Following the Solar Decathlon, the Black & White house will compete in Europe's own Solar Decathlon competition next year. The team eventually hopes to sell the house, with an asking price of $250,000.

Katy Tomasulo is Deputy Editor for EcoHome.

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