solar updraft tower: How small a working unit can be made? My reason to ask this question is: I think that if a commercial unit is ever to be built, first the concept must be widely established. One or two working examples of a size similar to the prototype built in Spain won't likely prove commercial usability. The huge billion dollar concepts are way too much money to sink into a radical concept. Small inexpensive home electrical generation projects may actually be built. So how small a chimney will work? Could multiple chimneys be arrayed together? How many in an array? Could the chimneys be built around a house or barn? Could the array of chimneys be a structure wider than it is high? How inexpensively could this type of power generation system be built when scaled for a single average home? Could the tower height be kept within suburban housing bylaws limits? I don't know about you, but I would rather see a photo of somebody's working backyard ugly kludge, than the most beautiful digital animated movie of a solar thermal updraft tower mega-project.