Editing Solar updraft tower (section)

== Efficiency ==
The traditional solar updraft tower has a power conversion rate considerably lower than many other designs in the (high temperature) [[solar thermal]] group of collectors. The low conversion rate is balanced to some extent by the lower cost per square metre of solar collection.<ref name="Mills"/><ref>{{cite web|url= http://www.eere.energy.gov/troughnet/pdfs/status-part1.pdf |title=3. Solar Energy Systems }}&nbsp;{{small|(1.24&nbsp;MB)}} Status Report on Solar Trough Power Plants (1996)</ref><ref>{{cite journal |doi=10.1016/S0038-092X(97)80946-2 |title=Solar electricity generation—A comparative view of technologies, costs and environmental impact |journal=Solar Energy |volume=59 |issue=1–3 |pages=89–99 |year=1997 |last1=Trieb |first1=Franz |last2=Langniβ |first2=Ole |last3=Klaiβ |first3=Helmut |bibcode=1997SoEn...59...89T }}</ref>

Model calculations estimate that a 100&nbsp;MW plant would require a 1,000&nbsp;m tower and a greenhouse of {{convert|20|km2}}. A 200&nbsp;MW tower of the same height would require a collector 7 kilometres in diameter (total area of about {{cvt|38|sqkm|sqmi}}).<ref name="Schlaich" /> One 200&nbsp;MW power station will provide enough electricity for around 200,000 typical households and will abate over 900,000 tons of greenhouse producing gases from entering the environment annually. The glazed collector area is expected to extract about 0.5 percent, or 5&nbsp;W/m<sup>2</sup> of 1&nbsp;kW/m<sup>2</sup>, of the solar energy that falls upon it. If a transpired solar collector is used in place of the glazed collector, the efficiency is doubled.

Additional efficiency improvements are possible by modifying the turbine and chimney design to increase air speed using a venturi configuration. Concentrating thermal [[Concentrated solar power|(CSP)]] or photovoltaic [[Concentrated photovoltaics|(CPV)]] solar power plants range between 20% and 31.25% efficiency ([[Dish Stirling#Dish designs|dish Stirling]]). Overall CSP/CPV efficiency is reduced because collectors do not cover the entire footprint. Without further tests, the accuracy of these calculations is uncertain.<ref>{{cite journal |doi=10.1016/j.solener.2005.04.001 |id={{INIST|17773321}} |title=Critical evaluation of solar chimney power plant performance |journal=Solar Energy |volume=80 |issue=5 |pages=535–44 |year=2006 |last1=Pretorius |first1=J.P. |last2=Kröger |first2=D.G. |bibcode=2006SoEn...80..535P |doi-access=free }}</ref>  Most of the projections of efficiency, costs and yields are calculated theoretically, rather than empirically derived from demonstrations, and are seen in comparison with other collector or solar heat transducing technologies.<ref>{{cite book |doi=10.1007/978-94-007-7275-5 |title=Harnessing Solar Heat |series=Lecture Notes in Energy |date=2014 |volume=18 |isbn=978-94-007-7274-8 |first1=Brian |last1=Norton }}{{page needed|date=June 2017}}</ref>

An innovative concept recombining a thermal power plant dry cooling tower with a solar chimney was first introduced by Zandian and Ashjaee<ref>{{cite journal |doi=10.1016/j.renene.2012.09.051 |title=The thermal efficiency improvement of a steam Rankine cycle by innovative design of a hybrid cooling tower and a solar chimney concept |journal=Renewable Energy |volume=51 |pages=465–473 |year=2013 |last1=Zandian |first1=A |last2=Ashjaee |first2=M |bibcode=2013REne...51..465Z }}</ref> in 2013 to increase the efficiency of the solar updraft towers. This hybrid cooling-tower-solar-chimney (HCTSC) system was shown to be able to produce an over ten times increase in output power compared to the conventional solar chimney power plants like [[Manzanares, Ciudad Real]], with similar geometrical dimensions. In addition, it was shown that with an increase in chimney diameter, the power generation can reach to MW-graded power output without the necessity of building huge individual solar chimney panels. The results showed a maximum of 3 MW power output from the HCTSC system which resulted in 0.37% increase in the [[thermal efficiency]] of a typical 250 MW [[fossil fuel power station|fossil fuel power plant]], with a chimney diameter of only {{convert|50|m|ft}}. The new hybrid design made the solar updraft tower feasible again, and proved it to be economical in saving much construction cost and time. This concept also recaptures the heat of radiators that are thrown out into the atmosphere without efficient utilization, and prevents generation of excessive greenhouse gasses.

The performance of an updraft tower may be degraded by factors such as atmospheric winds,<ref>{{cite book |doi=10.1115/HT-FED2004-56651 |chapter=Computing Flow in a Solar Chimney Plant Subject to Atmospheric Winds |title=Volume 2, Parts a and B |pages=1153–62 |year=2004 |last1=Serag-Eldin |first1=M. A. |isbn=978-0-7918-4691-9 }}</ref><ref>{{cite journal |doi=10.1080/01425910212851 |title=The effect of wind speed at the top of the tower on the performance and energy generated from _thermosyphon solar turbine |journal=International Journal of Solar Energy |volume=22 |issue=1 |pages=9–18 |year=2002 |last1=El-Haroun |first1=A. A. |bibcode=2002IJSE...22....9E |s2cid=108960377 }}</ref> by drag induced by the bracings used for supporting the chimney,<ref>{{cite journal |doi=10.1115/1.1530198 |title=Calculation of Pressure and Density in Solar Power Plant Chimneys |journal=Journal of Solar Energy Engineering |volume=125 |issue=1 |pages=127–9 |year=2003 |last1=von Backström |first1=Theodor W. }}</ref> and by reflection off the top of the greenhouse canopy.  However, updraft may be enhanced by crosswind at the upper level – creating a low pressure vortex across the top of the chimney would increase updraft.<ref>{{cite journal |last1=Watanabe |first1=Koichi |last2=Fukutomi |first2=Sho |last3=Ohya |first3=Yuji |last4=Uchida |first4=Takanori |title=An Ignored Wind Generates More Electricity: A Solar Updraft Tower to a Wind Solar Tower |journal=International Journal of Photoenergy |date=11 March 2020 |volume=2020 |pages=1–9 |doi=10.1155/2020/4065359 |doi-access=free |hdl=2324/3000484 |hdl-access=free }}</ref>