Each of the homes on the tour boasted a different and impressive technique.

Bob Grossman and his wife have dedicated the last three years to building an architecturally stunning and outlandishly efficient straw-bale home outside of Golden, Colo.

The Grossmans considered dozens of different materials when they decided to construct their own home, Bob said. They knew they wanted to use an alternative material.

The straw bales turned out to be the perfect material because they naturally insulate and are definitely a renewable resource.

“And I like round walls and smooth corners,” Bob said. “It just makes me feel good.”

The straw bales allowed the Grossmans to construct their home in whatever shape they pleased.

They have used passive solar, with huge floor-to-ceiling windows on the south side of the home and almost no windows on the north side.

“You don’t just take one technology, one thing, and have it work,” Bob said. “You have to have a whole system.”

The 5,700 square-foot home is equipped with several hydrothermal panels to heat water and six crystalline-Silicone photovoltaic panels on the roof. The home, which still isn’t occupied, will produce about 6.8 kilowatts of power once it’s connected to the grid and flipped on, Bob said. That’s more than enough for the home now while it’s mostly empty, he said. It uses only about 1.8 kilowatts. Whether or not the Grossmans will have net-zero power usage remains to be seen though, Bob said.

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Pictured: Bob Grossman shows the "brains" of his 5,700 square-foot straw bale home in Golden, Colo. to visitors on the solar tour. He used these plastic tubes to plum the entire home. He did it himself in two days, he said. The red ones will efficiently carry hot water heated by hydrothermal solar panels on the home's roof.