Cost. That was it. The project in Spain was significantly cheaper to build and was only a 50kw tower. The EnviroMission tower was going to be 200 MW facility. The benefits of the solar updraft tower are huge: Able to be built using readily available materials (concrete, glass, etc.) If a terrorist blows it up, just build another one. Tremendous tourism potential. The skirt/greenhouse could grow crops making the air denser and more efficient, and with a LOT of open land Australia would've been the perfect choice. Unfortunately it just came down to building cost.

A 1000m tower is expensive and long to build. We have never built something as high so far (tallest building so far is 828m).

Crazy thought - could a mountain be converted? Build two tunnels, one vertical, one horizontal. Probably crazily expensive, but known engineering...

Not sure if we have experience building such vertical tunnels in mountains though? This would have to be much, much larger than your regular mine.

I like the way you think!!!