Visitors tour the U.S. Department of Energy Solar Decathlon 2011 in Washington, D.C., Sept. 30, 2011, with Arlington, Va., left, and the Lincoln Memorial, right, in the background. (Photo credit: Stefano Paltera/U.S. Department of Energy Solar Decathlon.)

More than 4,000 students from universities around the world have descended on the National Mall’s West Potomac Park to showcase the highly energy efficient solar-powered houses they created for the DOE Solar Decathlon 2011, which kicked off Sept. 22 and runs through Oct. 2. Basically, this is an educational opportunity for future engineers and architects to design, build and operate solar houses that are not only energy efficient, but also attractive and easy to live in. It’s also an opportunity for the thousands of people expected to tour the 10 homes over 10 days.

While solar PV is usually the star of the show, many of the teams included solar hot water systems in their homes. And new this year is an affordability contest, which rewards teams that build houses with estimated costs at or below $250,000. The teams have to perform everyday tasks - such as cooking, laundry and washing dishes - to test the energy efficiency of their houses.

The contest results are not in yet - you can check the website