A no-fuss solar-powered building

The Boston team in the Solar Decathlon competition is shooting for affordability. Apart from the solar panels, they are using almost entirely building materials that can be found at local hardware stores.

Martin LaMonica
Martin LaMonica is a senior writer covering green tech and cutting-edge technologies. He joined CNET in 2002 to cover enterprise IT and Web development and was previously executive editor of IT publication InfoWorld.
Martin LaMonica
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Curio house

The Boston Architecture School and Tufts University are building the Curio House, a home that's designed to run entirely from solar energy. It's the Boston area's entry into the Solar Decathlon, a Department of Energy-run event where student teams from 20 universities compete for the best solar home design. Teams need to take apart and then reassemble their buildings on the National Mall in Washington, D.C., next month where they will be open to the public for 10 days and judged by a panel.

The Boston team has focused its design on affordability, making an 800-square-foot building using almost entirely off-the-shelf products and technologies. It has lined up a buyer for the home in Cape Cod where it is supposed to be the first unit in a green housing development. The projected cost of the building, big enough for two people and a small child, is about $200,000. Students, donors, and school administrators held a ribbon-cutting ceremony at the unfinished building on Thursday at Tufts University in Medford, Mass.

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Solar horsepower

A view of the home's energy source on the roof. On the left are two rows of photovoltaic solar panels--28 in all--that generate electricity and on the right is a row of five solar thermal panels that make hot water. The top-of-the-line SunPower PV panels will be able to generate 6.4 kilowatts of electricity, far more than a building this size would need. However, the designers need to over-engineer the home to feed batteries so the house can keep running even on cloudy days and evenings. Also, students are judged on how much excess electricity they can generate.

The building will have a much lower electrical load than most homes, not only because it's compact. It will be using EnergyStar-rated appliances and LED lamps for all fixed lighting. And the building will be insulated and well-sealed, using foam and tape to cover cracks, and up to R-40 worth of foam and celllose insulation. Because it will be well-insulated, its electrical heating and cooling system will have a lighter load.

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The SunPower panels will be equipped with microinverters, which are about the same size as the black connector boxes seen here. That's a technology that wasn't used heavily during the Solar Decathlon competition two years ago. Inverters are needed with solar electric panels to convert the direct current they generate into household alternating current. Right now, most installations use a few large inverters to do the job. But in the past two years, a number of companies have developed microinverters that convert DC to AC on each individual panel. This has historically added cost to the overall system but microinverters offer some advantages and better efficiency, say proponents. Each panel can be monitored for performance and shading on one panel won't decrease the output of panels wired to it, as happens with centralized inverters. For homeowners, microinverters means that homes can add just a few panels at a time as they are wired individually.

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Radiant heat

The solar thermal panels on the roof will make hot water for the kitchen and bathroom but also to heat the home. Here is a view of the radiant heat system that is under the floor of the structure. Hot water heated by the panels circulates through the tubes which are housed in these foam and metal casings.

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Supplemental heating system

Students from the Boston Architecture School and Tufts University discuss the Curio House after the ribbon-cutting ceremony. From here you can see the innards of the heating and cooling system, including the ducts and the fan mounted on the ceiling.

In addition to using solar-powered radiant floor heating, the building will use an air-source heat pump (similar to a ground-source heat pump) for heating and cooling. The system, made by Fujitsu, is a particularly efficient system because it uses a variable compressor, students explained. That means that the pump can react to changes in the thermostat in a more incremental way, rather than simply turning on or off as many air-source heat pumps work now.

Also note the flexible ducting used on one end of the building. Because this structure has to be taken apart and put back together for the competition, the builders chose materials that make assembly easy.

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Low-tech Blinds

In the spirit of using off-the-shelf components, the Boston team in the Solar Decathlon is using a simple plastic shading system on the south-facing windows. Unlike most blinds, however, they are placed on the outside to save indoor space.

The idea is to keep the shades down to keep heat from the sun out during hot times of the year and to open them to maximize incoming heat (and daylight) during cold times. One planned high-tech touch is the use of a "warm wall," or glass plates filled with two inches of liquid. This will act to retain heat during cold days, releasing heat into the room at night.

The overhang seen here was done deliberately to provide shade when the sun is higher during the summer but maximize incoming sunlight during the winter when light comes in at a lower angle.

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Energy recovery ventilator

A view inside the compartment that houses the building's mechanical systems, which can be accessed from the outside. Very well-insulated homes use a heat-recovery ventilator or an energy-recovery ventilator, which is pictured here. These systems circulate indoor air and bring in fresh outdoor air. They are efficient because they heat the incoming air that is being exhausted outside. An energy-recovery ventilator goes one step further and adjusts the humidity using a dessicant inside the unit.

Also stored in the compartment are the hot-water storage tanks, seen on left, that hold the water heated by the rooftop solar thermal panels.

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Tool box

A wider view of where the mechanical systems of the building are kept. The structure was designed to be modular so that it could be taken apart and put back together again for the competition in Washington, D.C., or, ultimately, for future houses to be built.

The "core" of the building houses the mechanicals, bathroom, and kitchen. Two other segments where the living space attach to that core. The Boston team will be using at least three flat bed trucks to bring the components down to Washington, D.C.

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Water tanks

Buildings in the Solar Decathlon competition are expected to make efficient use of water as well as energy. The Curio House from the Boston team will recycle run-off water and store it in these tanks. The water will be used to feed plantings around the front of the house.

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