A solar updraft tower generates electricity with nothing more than a greenhouse and a tall chimney. A 195 meter tall prototype in Spain cheaply operated at 50 kW for years. Now there are plans to build others, including a 40 MW tower, 750 meters tall (near twice as tall as the current tallest structure in the EU). Two others, a 200 MW tower in Australia (previously discussed) or a 400 MW tower in Namibia could become the tallest structure of any kind if built: 1km and 1.5km tall, respectively. Yet even those are dwarfed by the theoretical super chimney which could stand 5km tall and 1km wide. Such a tower would use the Earth's atmosphere itself as the greenhouse, could cause rain, reduce global warming and generate over 300,000 MW of "green" electricity. [more inside]
A kilometre-high solar tower, to be built in the Australian outback by EnviroMission Ltd, will become the world's tallest structure when completed in 2006. Designed by Jorg Schlaich of Schlaich Bergermann und Partner, the solar tower (or solar chimney) operates like a hydroelectric power plant, but uses hot air instead of water, and it could provide enough electricity for 200,000 homes. Time calls it one of the best inventions of 2002, and I think it's one of the most ingenious ideas I've ever heard. Another solar chimney project was planned in Rajasthan, India, but I haven't found any information on its current status.