WASHINGTON - A tidy village dedicated to the future of green, solar-powered living has taken over the heart of the National Mall, where 20 teams of college students are vying to see who can build the most appealing energy-efficient home.

The teams, from universities in North America and Europe, including Penn State, are competing in the Department of Energy's biennial Solar Decathlon, which runs through Oct. 18. The challenge: Design and build a prototype house that can provide the comforts of home while generating all the energy residents need from the sun's rays. Teams get bonus points if they can produce surplus electricity and sell it back to the power company.

Starting Sept. 30, student-led teams built sleek pyramids, rusty silos, reclaimed-water gardens, glassy boxes, and shaded porches. And each house sports an electric meter that can run in reverse, giving the team credit for each kilowatt it can sell into the local electric grid.

A decathlon, of course, consists of 10 events. These houses are being judged for their architecture, market viability, engineering, comfortable temperature and humidity, hot-water production, appliances, entertainment, communication with the public, lighting design, and ability to produce at least as much energy as they consume.

The competition is meant to push solar technology forward - and to train the next generation of architects, engineers, and design pros, said Richard King, who runs the project for the Energy Department.

One example of the cutting-edge approach would be Team Spain's entry, built by Universidad Politecnica de Madrid. Unabashedly modern, the house sits under a large inverted pyramid that contains solar-electric panels and solar-heating water collectors. The pyramid is attached to the roof with a ball-and-socket mechanism that pivots the pyramid to track the sun.

Virginia Tech's house incorporates sliding-glass walls on the north and south faces. The walls can be opened and closed automatically by an in-house computer linked to indoor climate sensors and an outdoor weather station. The walls can also be operated by iPhone.

The house designed by Technische Universitat Darmstadt in Germany - the school that took top honors in the last decathlon, in 2007 - is outfitted with an 11.1-kilowatt photovoltaic system designed to produce twice as much energy as the house consumes. The shiny, black, two-story structure is covered with single-crystal silicon solar panels on the roof and abut 250 thin-film solar panels on all four sides.