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Energy geeks compete for coolest solar home

Upcoming Solar Decathlon contest will judge 20 solar-powered homes built by college students. MIT's entry is already under construction. Photos: MIT's solar house

CAMBRIDGE, Mass.--Right behind the solar car on every environmentalist's wish list is a home powered entirely by the sun.

This summer, teams from 20 universities are busy building enough homes to make an entire "solar village." The off-grid, self-powering homes will be on display for 10 days in October on the National Mall in Washington D.C., competing in the Department of Energy's 2007 Solar Decathlon.

A group from the Massachusetts Institute of Technology has already begun construction of its off-grid solar-powered home, called MIT Solar 7 and drawing in students and advisers with expertise in everything from electrical storage to mechanical engineering. It's part of an MIT-wide commitment to energy-related research to address climate change.

The team's 800-square-foot home, going up in a crumbling parking lot near the MIT campus, combines energy-efficient design with the latest in solar technology: a passive solar-heating system and a photovoltaic array big enough to not only operate the house but also power an electric car.

The project's student leader, Corey Fucetola, is an electrical engineering graduate student whose thesis is in nano-material fabrication--a topic that has little to do with sustainable architecture. But Fucetola says he is learning a lot of valuable information that can benefit himself, the community and providers of green-building products.

"I'd like to be knowledgeable on the subject (of sustainable building) because I know that energy and pollution are intrinsically linked with population growth. Inevitably, I'll be part of the problem when I build a house," he said.

The point of the competition is not to create new building technologies. On the contrary, entrants have to use commercially available products to demonstrate that a sun-powered home can be commercially reproduced. For a university like MIT with access to high-efficiency, NASA-grade solar electric panels, that was an unwelcome constraint.

"You can't yank something out of the lab and throw it onto your roof. You have to use commercial, production-grade products," said Kurt Keville, the project's faculty adviser and a researcher at MIT's Institute for Soldier Nanotechnologies. "I was heartbroken."

Still, the MIT group, which is made up of about 20 volunteers, was able to tap into its own heritage: it is using energy-efficient windows originally developed at MIT that use krypton gas as an insulator between three panes of glass.

Speeds and feeds
For any passive solar home, thermal mass--material that retains heat from sunlight--is critical. MIT Solar 7 (named because it is the seventh solar home built by MIT since 1939) will use a wall made of 1-foot-thick multi-layered tiles that will hold water and a high-tech insulator called an aerogel. When finished, the wall will hold about 60 gallons of water which, along with the aerogel, will retain heat and cold air while letting in light, said Keville.

That south-facing wall will also hold 60 evacuated tubes, which will heat water that is circulated through a radiant heating system using Warmboards, a subfloor system made up of insulated plastic water tubes. This system is far more efficient than traditional home heating systems and more comfortable to people because the heat rises evenly from the floor, Keville said.

"We're getting maximum use out of the BTUs that we are generating from the hot water. This will be a hot product soon because it's so efficient," he said.

During the homes' installation on the National Mall, participants are judged on how well their house performs by hosting a dinner party and doing loads of laundry with hot water.

To power the Solar 7, the MIT crew is installing a 9-kilowatt solar array--much bigger than what houses of this size would typically need. The electricity will be stored in 24 batteries capable of holding 70 kilowatt-hours, which can run the home in the absence of sun and be recharged in two days.

The excess power is essential to the competition, as Solar Decathlon contestants are judged on how far they can drive their DOE-provided electric car.

The building will also be wired with sensors to measure the fluctuations in temperature, which is a way for judges to gauge the builders' ability to maintain a comfortable indoor climate. That information can also serve prospective owners looking to track their energy consumption, noted Fucetola.

Sustainable design
But for all its high-tech components, good architectural design is perhaps the most challenging aspect of the project. That's in addition to making it a livable space with room for a bedroom, full bathroom, dining area and living room.

For starters, the house needs to be modular and assembled by nonprofessional builders because contestants need to transport and reassemble their creations on the National Mall. The initial design, which originally came out of a sustainable architectural workshop, needed to be substantially altered to make dismantling and reassembly easier, said Keville, adding that the entire house will be held together by screws, not nails.

Design choice can also substantially reduce the amount of energy required to run a home. For example, the house's roof will maximize the amount of daylight that comes in, thereby cutting down on electricity requirements. At the same time, the roof is angled so light doesn't pour in during the hottest part of the day.

Similarly, MIT Solar 7 will have a front awning and windows on the opposite side of the house to maximize air flow through the home, which provides clean air and helps cool it.

"One of the guiding principles is that we would be using daylighting and natural ventilation as much as possible," Fucetola said.

Also planned is a water-reclamation feature that will collect runoff water and store it for landscaping, and a roof that the designers hope will prevent ice buildup.

As the student lead on the project, Fucetola, who spends four days a week at the site, has become something of an evangelist, recruiting volunteers by asking interested passersby to get involved. "I tell people in elevators about this," he said.

The team hopes to sell off its creation as a way to fund MIT's entry in the next Solar Decathlon competition in two years. (Realtors have expressed interest.)

So will MIT Solar 7 live up to its billing and be a "net zero energy" solar home? Keville says the home will generate more electricity than it consumes for most of the year.

"We know for nine months of the year that we'll be net energy positive," he said. "We may be break-even in January and February. We'll find out when we bring it back to Cambridge."