Editing Solar updraft tower (section)

== 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 {{convert|7|km|mi|1}} in diameter have been discussed. A larger chimney height increases the pressure difference via the [[stack effect]]; chimneys as tall as {{convert|1000|m|ft|0}} have been discussed.<ref>{{cite book|title=Renewable energy technology, economics, and environment|date=2007|publisher=Springer|location=Berlin|isbn=978-3-540-70949-7|page=223|editor=Martin Kaltschmitt|editor-link=Martin Kaltschmitt|editor2=Wolfgang Streicher|editor3=Andreas Wiese}}</ref>

Heat is stored inside the collector area allowing SUTs to operate 24 hours a day. The ground beneath the solar collector, water in bags or tubes, or a [[solar pond|saltwater thermal sink]] in the collector could add thermal capacity and inertia to the collector. Humidity of the updraft and release of the [[latent heat]] of condensation in the chimney could increase the energy flux of the system.<ref name="Solar pond tower for 5 €ct/kWh">{{cite web|url=http://www.greenidealive.org/110599/466/solar-pond-tower-for-5-ct/kwh.html |title=Solar pond tower for 5 €ct/kWh|publisher=GreenIdeaLive |access-date=2011-09-11}}</ref><ref name="Schlaich">{{cite journal |doi=10.1115/1.1823493 |title=Design of Commercial Solar Updraft Tower Systems—Utilization of Solar Induced Convective Flows for Power Generation |journal=Journal of Solar Energy Engineering |volume=127 |pages=117–24 |year=2005 |last1=Schlaich |first1=Jörg |last2=Bergermann |first2=Rudolf |last3=Schiel |first3=Wolfgang |last4=Weinrebe |first4=Gerhard }}</ref>

[[Wind turbine|Turbines]] with a horizontal axis can be installed in a ring around the base of the tower, 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.

A nearly negligible amount of [[carbon dioxide]] is produced as part of operations, while construction material manufacturing can create emissions.<ref>{{cite conference |last1=Niemann |first1=H.-J. |last2=Lupi |first2=F. |last3=Hoeffer |first3=R. |last4=Hubert |first4=W. |last5=Borri |first5=C. |conference=5th European & African conference on wind engineering |location=Florence Italy |date=July 2009 |title=The Solar Updraft Power Plant: Design and Optimization of the Tower for Wind Effects |publisher=Firenze University Press |url=https://www.iawe.org/Proceedings/5EACWE/136.pdf |doi=10.1400/116481 }}</ref> Net energy payback is estimated to be 2–3 years.<ref name="Schlaich"/>

Since solar collectors occupy significant amounts of land, deserts and other low-value sites are most likely. Improvements in the solar heat collection efficiency by using unglazed [[transpired collector]] can significantly reduce the land required for the solar array.

A small-scale solar updraft tower may be an attractive option for remote regions in developing countries.<ref>{{cite journal |doi=10.1016/j.fuel.2006.04.029 |title=The potential of solar chimney for application in rural areas of developing countries |journal=Fuel |volume=85 |issue=17–18 |pages=2561–6 |year=2006 |last1=Onyango |first1=F |last2=Ochieng |first2=R |bibcode=2006Fuel...85.2561O }}</ref><ref>{{cite journal |doi=10.1016/S0960-1481(02)00227-6 |id={{INIST|14497497}} |title=Case study of solar chimney power plants in Northwestern regions of China |journal=Renewable Energy |volume=28 |issue=8 |pages=1295–304 |year=2003 |last1=Dai |first1=Y.J |last2=Huang |first2=H.B |last3=Wang |first3=R.Z |bibcode=2003REne...28.1295D }}</ref> The relatively low-tech approach could allow local resources and labour to be used for construction and maintenance.

Locating a tower at high latitudes could produce up to 85 percent of the output of a similar plant located closer to the equator, if the collection area is sloped significantly toward the equator. The sloped collector field, which also functions as a chimney, is built on suitable mountainsides, with a short vertical chimney on the mountaintop to accommodate the vertical axis air turbine. The results showed that solar chimney power plants at high latitudes may have satisfactory thermal performance.<ref>{{cite journal |doi=10.1016/j.solener.2005.01.003 |id={{INIST|17275884}} |title=Solar chimney power plants for high latitudes |journal=Solar Energy |volume=79 |issue=5 |pages=449–58 |year=2005 |last1=Bilgen |first1=E. |last2=Rheault |first2=J. |bibcode=2005SoEn...79..449B }}</ref>