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Interlock House


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Adobe Flash Video: This video shows the placement of the house's electrical components, photovoltiac array, and inverters.

This presentation contains no sound.

Photovoltaic modules, or solar panels, convert sunlight into direct current electricity. After attaching an array of photovoltaics to an inverter, which converts direct current to alternating current, the electricity can be used to power household devices or fed into the power grid.

Our main photovoltaic array consists of Sayno HIT modules that each produce 205 watts. Once all of the panels are connected, our array will produce a total of 7.8 kilowatts—roughly double what the Interlock House needs to operate.

In past competitions, each house stood alone and stored its excess energy in an array of batteries. In the 2009 competition, houses will be grid-tied, meaning that excess energy will be fed into the Washington, D.C., power grid. As a net producer of energy the power meter on our house will actually run in reverse during daylight hours.

Our 7.8 kilowatt array cost $40,000 in January 2009. The modules have an efficiency of 18 percent (meaning that 18 percent of the sunlight that strikes them is converted into electricity). The panels have a life span of 20 years. Dividing the total cost by energy savings per year, our array will generate a return on investment (ROI) in 18 years. This estimate does not take into account any incentive packages or utility company rebates for feeding energy back into the grid. Depending on the incentives available to a community, the time frame for an ROI could be considerably shorter.

Find out more about grid connection and incentive programs in your area:

Thin Film Photovoltaics

PowerFilm can be mounted onto a flexible backing

In addition to a conventional photovoltaic array, the Interlock House features a smaller array composed of PowerFilm thin film modules.

Thin film photovoltaics are a cheaper alternative to the silicon wafers that account for 40-50% percent of a conventional photovoltaic panel’s cost. The materials used in thin film absorb more light than their traditional silicon cells and therefore can much thinner than their traditional counterparts (1 micron vs. 200 microns)—so thin, in fact, that thin film cells can be printed or laser inscribed onto a flexible backing. The combination of smaller size and lower price have made it possible to begin incorporating thin film into building materials themselves, or building integrated photovoltaics (BIPV).

Thin film is still an emerging technology, and though it has great potential, products currently available on the market have maximum efficiencies of around nine percent.

On the Interlock House, thin film solar cells will be integrated with window louvers on the eastern and southern sides of the house, as well as with the tracking louvers above the sun porch. The Interlock House thin film array is rated at 270 watts.

Find out more about thin film and its applications:

Passive Tracking Louvers

Directly above the sunspace, the Interlock House will feature a system of tracking louvers. Covered in thin film, these student-designed, prototype louvers will utilize a system of shades, balancing fluids, and movement dampers to follow the sun as it moves across the sky. The systems is passive because it does not rely on motors or electrical devices to function.

On the sides of each louver are two tubes filled with balancing fluid (a gas which expands and contracts based on temperature). As the sun moves across the sky, sunlight strikes one of the two tubes, causing the fluid inside to expand. Connected by a flexible hose, the expanding fluid can move freely between tubes, causing one side of the louver to become heavier than the other. The louvers are secured on pivots and can rotate freely based on their weight, resulting in their potential to follow the sun’s movement without human or electronic input. Dampers limit the rate at which the pivots can move, preventing sudden gusts of wind from upsetting the system.

Photovoltaic modules convert the most sunlight into electricity (efficiency) when sunlight hits their surface at a 90 degree angle. Thus, the ability to track the throughout the day can result in significantly increased energy output. Although only a prototype, this system is similar to systems already deployed on large solar arrays, except on a much smaller scale.

Artificial Lighting

The Interlock House has been designed to include a balance of ambient and task lighting. In keeping with our team’s commitment to universal design, special attention was paid to the role of lighting and colored surfaces for individuals with poor or deteriorating vision.

Our design called for a layered approach to lighting. The lights themselves are a combination of compact fluorescent (CFL), halogen, and light emitting diodes (LED). Fluorescent fixtures are used for ambient lighting and are found in both wall-washing and ceiling-mounted pendant fixtures. LED and halogen fixtures provide task direct lighting for increased illumination near the bed, desk, and kitchen counters. Finally, a series of solar-powered LED devices are employed along the edges of exterior planters and benches to provide increased comfort and safety while reducing the house's contribution to light pollution in urban areas. The wide spectrum of fixtures and color warmth allow a resident to modify the house’s ambiance throughout the day, and across seasons.

For more information about lighting fixtures and energy conservation in your home:


The appliances in the Interlock House were chosen for efficiency. Sometimes efficiency means simply having a smaller appliance because it requires less electricity than a larger model. This is especially true in our selection of refrigerator and dishwasher, which are both large enough to meet the needs of the competition but remain relatively small in size. With the exception of the dishwasher, all of our appliances are Energy Star rated meaning they use 20-30% less energy than models that are not Energy Star certified. The appliances we are using are listed below:

  • Refrigerator: Summit CP171SS
  • Dishwasher: Frigidaire FMB330RGC
  • Oven: Whirlpool RBS245
  • Induction Cook Top: Summit SINC2220
  • Washer/Dryer: LG WM3431HS

The induction cook top uses less energy because it more efficiently transfers energy to pots and pans, cooking in about half the time of a conventional electric resistance cook top. The washer and dryer are combined into a single unit, which removes the need to transfer clothes between machines and allows start-to-finish washing and drying control from one dial. During the drying cycle sensors automatically shut off the appliance once the load is dry, preventing unnecessary energy consumption.

To learn more about energy efficient appliances:

Major sponsors Iowa State University U.S. Department of Energy Solar Decathlon U.S. Department of Energy National Renewable Energy Laboratory