It’s been a soggy start to the Solar Decathlon 2011 on the National Mall's West Potomac Park in Washington, D.C. With two to four inches of rain threatened, there is little chance of sunny skies this weekend for the 19 collegiate teams participating in the event. So far the University of Maryland is ahead in the competition that challenges teams to build solar homes that are cost-effective, energy-efficient and attractive.

Rounding out the top three are Team China and Purdue University. The teams arrived at the park 10 days ago to start constructing their homes. They are open to the public starting today and continuing through Sunday October 2. Scoring will continue all week.

When the sun is shining, the solar panels on the houses produce electricity that is used to power appliances, lights, mechanical systems and electronics. Any excess energy flows from the houses through a small village power grid, or microgrid and to the Washington, D.C., community. When there is little or no sunshine, the utility delivers energy back to the solar village without an interruption in service. So far, the homes have consumed more energy than they’ve produced but the energy balance may switch later in the week when the skies brighten.

Sponsored by the Department of Energy, the Solar Decathlon has been held every two years since 2005. Teams earn points on 10 tasks in three ways: Completing household tasks such as cooking, washing dishes and doing laundry; meeting specified criteria, such as maintaining a comfortable (71 to 76 degrees F) indoor temperature and earning points from judges on features that can’t be measured such as aesthetics and design inspiration.

Since 2002, 72 houses have competed in the Solar Decathlon. After the competition, the houses are rebuilt and used for research or put on exhibit or even used as private homes. Silo House, which was built by a team from Cornell University in 2009, was sold to a private buyer and is now used as a residence on Martha’s Vineyard. Penn State sold its 2009 Natural Fusion house to a sponsor and it’s now being used as a conference center. Ohio State’s Solar House I was rebuilt at the Columbus Zoo and now welcomes visitors to the Polar Frontier exhibit, which features two polar bears—Anana and Aurora.