Australia plans to build the world's tallest tower that will actually be a 200 megawatt power plant. The structure will be one kilometer high and sit in a 4 mile diameter glass magnifier that will heat the air beneath it, and via convection, push it to the top, spinning turbines to generate the power. The cost? $1 Billion. The cost to build a natural gas fired 200 MW turbine power plant is about $100 Million. The big benefit is obviously the renewable fuel source and its inherent non-polluting characteristics. The downsides are: <li>It only works during daylight <li>The huge real estate investment (admittedly not a problem in New South Wales) <li>The 10X install cost <li>Maintenance and fragility of the optics <li>It makes a for a very inviting target My question would be, is this a cost effective endeavor? How much value can be placed on its green characteristics?