Twenty teams will show off their futuristic creations at the third edition of "Solar Decathlon 2007" between October 12-20 in the US capital's vast Mall esplanade, and 125,000 people are expected to visit the homes.
Construction and engineering experts will judge the homes using 10 criteria including architecture, engineering, market viability, interior comfort and whether the sun actually powers appliances and produces hot water.
The solar power going through the homes must also be able to charge an electric car.
The Energy Department says it organizes the contest to encourage students to pursue science and engineering careers, raise awareness about renewable energy and "help move solar energy technologies to the marketplace faster."
The young homebuilders, most of them 20-23 years old, watched gingerly as cranes deposited their creations on the Mall more than a week ahead of the competition.
The architecture, engineering, mechanics and electricity students come from German, Spanish, Canadian and American universities.
"They have to design, build, operate the most liveable, energy efficient, completely solar-powered house," Energy Department spokesman Chris Powers told AFP.
The department gave each team 100,000 dollars, which Powers admitted is not enough to build a house but helps the contestants get their projects started. It is up to the students to find sponsors to pay for the construction.
The winner's prize: "nothing but prestige," said Powers.
Most teams, consisting of 20 to 40 students, began their projects two years ago.
Students of Germany's Darmstadt University of Technology built a 38-tonne house made entirely of glass. They began designing it in May 2006 and started construction a year later.
After a tricky ocean voyage from Germany to Baltimore, a port city north of Washington, the house made it to the Mall.
"Now it's there, perfectly on time," said Darmstadt student Christian Stumpf.
Nearby, University of Texas students don hardhats in the shape of cowboy hats. Their house features an orange bowl-shaped, solar-heated hot tub.
"The plus of our house is the fun of it," boasted Texas student Sutton Giese.
Sixteen US universities are participating in the contest, including the prestigious Massachusetts Institute of Technology, Carnegie Mellon, Cornell, Penn State and the winner of the 2002 and 2005 Solar Decathlon, the University of Colorado.
In addition to Darmstad, Europe is represented by Polytechnic University of Madrid. Canada features Team Montreal, which includes McGill University, University of Montreal and Ecole de Technologie Superieure.
This year, Powers said, "We have to hope for the sun. Last time it rained the entire time of the contest."