@babalaas- I read about those towers. I saw an article about one in Spain that outperformed expectations and has lasted well beyond the expected lifespan of the project. I have also read about a proposed project in Australia that will generate about as much power as a gas fired plant. The article I read stated that the tower would be about 2000 feet tall, and the greenhouse would be about three miles in diameter.
The major drawback was the amount of land space necessary to create the project. Each large project literally requires a few square miles of land, which can make them cost prohibitive in the industrialized world. The height of the tower would also make them an eyesore, possibly riling up the NIMBY crowd.
The benefits however are numerous. The projects have very low operating costs, they work in all climates, they use proven technology, and they could provide large amounts of renewable energy to areas of the world where there are large tracts of marginal land. The towers can also be used to remediate poor quality land by trapping moisture. The greenhouse can then be used to grow cash crops as well as produce power.