motivation - principle - [technology] - energy production costs
		Solar updraft towers are large-scale power plants with an output of 5 to 200 MW each. For that the glass roof has to be several kilometers in diameter and the tube has to be as high as possible to achieve a large annual output. A 100 MW plant will produce about 750 GWh/year at 2.300 kWh/m2 global horizontal radiation. Fig. 5: The tower tube of a solar updraft tower during construction   For the chimney we thoroughly compared various types of construction and materials and discovered that for all desert -countries in question reinforced concrete tubes promise the longest life-span at least costs. Technologically speaking they are nothing but cylindrical natural draught cooling towers. For a 100 or 200 MW plant a suitable height would be 1.000 m with a diameter of 130 m. In this case the wall thickness decreases from 99 cm to 25 cm, and stiffening spoked wheels are placed on the inside. (Fig. 5)			The glass roof is constructed simply of square suspended roof segments say 9m x 9m (Fig. 6). We successfully tested this type at a prototype in Spain for several years and also managed to control the costs rather well. The shrouded turbines are basically more closely related to the pressure-staged hydroelectric turbines than to the speed-stepped wind turbines. Therefore we developed and designed them in collaboration with hydroelectric power plant manufacturers. Either a large number of small turbines with horizontal axes may be arranged around the base of the chimney, or to be more cost-efficient, one large, say a 100 MW turbine with a vertical axis is placed in the chimney’s cross-section. Fig. 6: The glass collector roof of a solar updraft tower.