Design
Power output depends primarily on two factors: collector area and chimney height. A larger area collects and warms a greater volume of air to flow up the chimney; collector areas as large as 7 kilometres (4.3 mi) in diameter have been discussed. A larger chimney height increases the pressure difference via the stack effect; chimneys as tall as 1,000 metres (3,281 ft) have been discussed.
Telescopic collapsible features can enable chimneys to be lowered to prevent storm damage.
Heat can be stored inside the collector area. A saltwater thermal sink in the collector could 'flatten' the diurnal variation in energy output, while airflow humidification in the collector and condensation in the updraft could increase the energy flux of the system.
Turbines can be installed in a ring around the base of the tower, with a horizontal axis, as once planned for an Australian project and seen in the diagram above; or—as in the prototype in Spain—a single vertical axis turbine can be installed inside the chimney.
Carbon dioxide is emitted only negligibly as part of operations. Manufacturing and construction require substantial power, particularly to produce cement. Net energy payback is estimated to be 2–3 years.
Since towers occupy significant amounts of land, deserts and other low-value sites are most likely.
A small-scale solar updraft tower may be an attractive option for remote regions in developing countries. The relatively low-tech approach could allow local resources and labour to be used for construction and maintenance.
Solar updraft towers can be combined with other technologies to increase output. Solar thermal collectors or photovoltaics can be arranged inside the collector greenhouse. This could further be combined with agriculture.
Read more about this topic: Solar Updraft Tower
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—Henry David Thoreau (1817–1862)