World's Tallest Man-made Structure Proposed

"If built, a proposed 200-megawatt "solar chimney" for rural Australia would become the most daring application yet of a quirky form of generating alternative, renewable electricity...A circular greenhouse with an upward sloping roof toward the center would draw heated air through electricity-generating turbines before allowing it to escape through a central 'chimney'...[It] is going to require a circular greenhouse almost 2.5 miles in diameter, enclosing a total area of more than six square miles...That would make it one of the largest man-made structures...ever built. The second engineering challenge is building the chimney that -- at 3,250-feet high -- would be more than twice as tall as the world's highest building, Kuala Lumpur's 1,569-foot high Petronas Tower."