So there are some issues which make it unlikely that this technology will be competitive. What do I think is the best reason for these not generating electricity in any competitive way? No one has bothered to build any except for prototypes … which have been abandoned. Smart people reinvent variations of these things fairly often. The solar updraft tower was first proposed in 1903. The first patent on the downdraft tower dates from 1975. People get enthused about them, get people to invest, build prototypes which don’t work as hoped. The prototypes get abandoned and hopefully get torn down. There are a few around, and they pop up in speculative fiction occasionally, but they just aren’t economically viable in reality. http://cleantechnica.com/2014/07/03/energy-towers-behind-rd-funding-pleas-hype/