Nearly 25,000 people visited the Solar Decathlon on the National Mall in Washington, D.C., Oct. 9, 2005. Photo by Steven A. Novy, AIA, Green Line Architects.

In fall 2007, the teams will transport their 700-square-foot solar houses to the National Mall, where they will form a solar village. The teams then compete in 10 contests to determine an overall winner. Using only energy from the sun, the teams generate enough electricity to run a modern household.

The 2005 competition featured a number of new and customized energy-producing and energy-efficient technologies. They included two new kinds of structural insulated wall panels (SIPs), a customized “solar chimney,” a fuel cell energized by solar-produced hydrogen, and an energy recovery ventilator.

The University of Colorado’s 2005 entry was chosen Overall Competition Winner and featured a unique “take” on the traditional SIP. For the walls, the team combined two off-the-shelf green building components into one newly patented SIP. The Colorado team’s “BioSIP” was like a giant ice cream sandwich made of two panels of Sonoboard - a strong but lightweight board made of recycled materials by Sonoco Co. - that are filled with BioBase 501, a lightweight foam insulation made from soybean oil by BioBased Systems.

To increase the energy efficiency of its competition home, the Washington State University team showcased a new type of SIP designed by an architect in Spokane. In the team’s version, a corrugated steel frame was encased by polystyrene material. This innovation allowed electrical wiring and plumbing to be run through the SIP without compromising its structural integrity.

The solar chimney concept was based on the simple principle that warm air, being less dense than cooler air, rises. In some solar chimney designs, warm air moves up a very tall, narrow tower through a turbine to generate electricity.

The University of Michigan team decided to adapt a much smaller version to provide passive solar heating and cooling to its Solar Decathlon home. In this solar chimney, sunlight heated the air in glass spaces at the base of the home’s south wall. The heated air would then rise along the curve of the roof and be either directed into the house by means of specially placed louvers for heating in winter, or released outside to cool the home in summer. The layer of air in the chimney provided convective and radiant heating control and added insulation.

The team from the New York Institute of Technology also customized solar and renewable energy technologies for its 2005 competition home. The team used some of the electricity generated by its roof-mounted photovoltaic system to separate the hydrogen and oxygen in water through a process known as “electrolysis.” The hydrogen was then stored and used later to power a fuel cell that produces electricity and heat on demand. Fuel cells, like batteries, convert the energy produced by a chemical reaction into usable electric power.

Cornell University’s team customized an energy recovery ventilator (ERV) to provide heating and cooling to its 2005 competition home. The ERV housed a silica gel wheel, also known as a desiccant dehumidifier, which transferred heat and humidity between the home’s intake and exhaust airstreams. The Cornell team’s ERV was coupled with an electric heat pump and an air handler. A fully automatic computerized control system was able to operate the ERV, as well as the rest of the heating and cooling system.

The Solar Decathlon is a competition sponsored by the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy in partnership with its National Renewable Energy Laboratory. The American Institute of Architects; American Society of Heating, Refrigerating and Air-Conditioning Engineers; the National Association of Home Builders; BP; and Sprint are partnering with DOE as title sponsors.

For more information on the 2007 event, visit http://www.eere.energy.gov/solar_decathlon/.