http://en.wikipedia.org/wiki/Solar_updraft_tower
It's a big tower surrounded by glass. The air under the glass gets heated by the sun and goes up trough the tower spinning the generators
This technology is very simple, almost perfect I say, one such tower could work for hundreds of years if maintained
Australia plans to build one with a collection area of 7km in diameter.
Spain built one with an area of 244 m diameter, it worked for 8 years and generated some 50kW at it's maximum, until it was closed due to "structural problems"
I would like to see these towers wherever there is space for them, their simplicity is inspiring