EnviroMission of Australia couldn't get their solar updraft tower done in Australia, so they have turned to Arizona to build their tower. The concept is simple. A large (5500 acre) circular greenhouse has a slight slope from 10 feet at the edge to 50 feet in the center in a low cone shape. A 2500 foot plus hollow concrete cylindrical tower is placed at the center. The greenhouse heats the air around the edge of the tower and it rushes towards the center as it rises. Hot air rises. The taller the tower, the faster the air rises due to the suction created by the chimney effect. A series of wind turbines placed at the base of the tower harness the energy of the wind that is created. Also, the change in temperature between day and night would actually allow the tower to operate, albeit at a lower capacity, when the sun sets. The temperature of the ground is almost never the same as the air temperature. Also, after the tower is built it will not have a negative impact on the environment since the same amount of heat will fall on the site whether it is built or not, so it won't contribute to global warming after it is built!
They already have a 200 MW power purchase agreement with the Southern California Public Power Authority and they say that they will have a final design between March and June of 2012.
Follow the link for the article.
http://www.enviromission.com.au/irm/.../TallVisionary
There is also a Wikipedia article on the company and the project.
http://en.wikipedia.org/wiki/Enviromission
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