Photos: Groups Show Off Green Initiatives

A simple solution to high heating bills just may be in your recycling bin.

It's the argument three sixth graders from made on Thursday night at the Fourth Annual Vienna Green Expo, where they showed off the solar thermal heater they built and designed using 130 recycled aluminum cans.

They were among the 35 vendors, businesses and community organizations who filled the , trading trips for more green, sustainable living and showcasing projects and products.

Margaret Covey, Ellie Renshaw and Ani Kalousdian started building the heater in December as part of the Siemens "We Can Change The World Challenge," a national competition for young scientists. They named it "STEP": Solar Thermal Energy Panel.

Renshaw said after soaking and painting the cans black to absorb more heat, the group put the cans in an insulated wooden box, covering it with glass from a re-purposed storm door.

They connected it to a trailer outside their school over several weekends in March, pulling air from the trailer through a pipe and pushing it through the columns of cans with a used computer fan, powered by a solar photovoltaic panel.

The air is warmed by the sun through the cans and pushed back into the trailer.

On their most successful trial run, they had raised the temperature inside the trailer by seven degrees, Covey said. If used consistently, the group said, it could save buildings hundreds on heating bills.

The students were one stop on a trail of tables and booths kids at the expo could visit for a stamp on their Green Passport. Vendors checked off boxes after kids and teens learned something new; students dropped the passports in a raffle bin to win prizes.

Among the other stops that drew a crowd: the Vienna Farmers Market table, which rewarded correct answers to trivia questions with fresh apples, and a Town of Vienna table that explained the town's new recycling and trash collection procedures and showed off plants grown in its own greenhouse. The plants -- including edible plants like basil -- will be sold during a plant sale in May.

For more photos from the event, click through the gallery in the media player above