Solar updraft tower 213555 224813642 2008-07-10T15:10:01Z Gh5046 1666666 /* Prototype in Spain */ Adding link for [[guy-wire|guy ropes]] [[Image:Solar updraft tower.svg|thumb|right|400px|Schematic presentation of a Solar updraft tower]] :''This article is about a type of power plant. For other uses of the term "Solar Tower", see [[solar tower (disambiguation)]]. For the use of solar energy for ventilation, see [[Solar chimney]].'' The '''solar updraft tower''' is a proposed type of [[renewable energy|renewable-energy]] [[power plant]]. Air is heated in a very large circular [[greenhouse]]-like structure, and the resulting [[convection]] causes the air to rise and escape through a tall tower. The moving air drives [[turbines]], which produce [[electricity]]. A research prototype operated in [[Spain]] in the 1980s. ==Description== The generating ability of a solar updraft power plant depends primarily on two factors: the size of the collector area and chimney height. With a larger collector area, more volume of air is warmed up to flow up the chimney; collector areas as large as 7 km in diameter have been considered. With a larger chimney height, the pressure difference increases the [[stack effect]]; chimneys as tall as 1000 m have been considered. Further, a combined increase of the collector area and the chimney height leads to massively larger productivity of the power plant. Heat can be stored inside the collector area greenhouse, to be used to warm the air later on. [[Water]], with its relatively high [[specific heat capacity]], can be filled in tubes placed under the collector increasing the energy storage as needed.<ref name="Schlaich">{{cite journal | author=Schlaich J, Bergermann R, Schiel W, Weinrebe G | 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 | issue=1 | year=2005 | pages=117–124 |url=http://www.sbp.de/de/html/contact/download/The_Solar_Updraft.pdf |format=PDF |doi=10.1115/1.1823493}}</ref> [[Wind turbine|Turbines]] can be installed in a ring around the base of the tower, with a horizontal axis, as planned for the 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 while operating, but is emitted more significantly during manufacture of its construction materials, particularly [[cement]]. Net energy payback is estimated to be 2-3 years.<ref name="Schlaich"/> A solar updraft tower power station would consume a significant area of land if it were designed to generate as much electricity as is produced by modern power stations using conventional technology. Construction would be most likely in hot areas with large amounts of very low-value land, such as deserts, or otherwise [[Land degradation|degraded]] land. A small-scale solar updraft tower may be an attractive option for remote regions in developing countries.<ref>{{cite journal | author=Onyangoa FN, Ochieng RM | title=The potential of solar chimney for application in rural areas of developing countries | journal= Fuel | volume=00 | issue=0 | year=0000 | pages=000–000 |doi=10.1016/j.fuel.2006.04.029}}</ref><ref>{{cite journal | author=Dai YJ, Huang HB, Wang RZ | title=Case study of solar chimney power plants in Northwestern regions of China | journal=Renewable Energy | volume=28 | issue=8 | year=2003 | pages=1295–1304 |doi=10.1016/S0960-1481(02)00227-6}}</ref> The relatively low-tech approach could allow local resources and labour to be used for its construction and maintenance. == History == In 1903, Spanish Colonel Isidoro Cabanyes first proposed a solar chimney power plant in the magazine ''La energía eléctrica''.<ref>{{sp icon}} {{cite paper |author=Lorenzo |language=Spanish |url=http://www.fotovoltaica.com/chimenea.pdf |format=PDF |title=Las chimeneas solares:De una propuesta española en 1903 a la Central de Manzanares |publisher=De Los Archivos Históricos De La Energía Solar}}</ref> One of the earliest descriptions of a solar chimney power plant was written in [[1931]] by a German author, [[Hanns Günther]]. Beginning in [[1975]], Robert E. Lucier applied for [[patent]]s on a solar chimney electric power generator; between 1978 and 1981 these patents (since expired) were granted in Australia,<ref>{{Cite patent|AU|499934B}}, "Apparatus for converting Solar to Electrical Energy"</ref> Canada,<ref>{{Cite patent|CA|1023564}}, "Utilization of Solar Energy"</ref> Israel,<ref>{{Cite patent|IL|50721}}, "System and Apparatus for Converting Solar Heat to Electrical Energy"</ref> and the USA.<ref>{{Cite patent|US|4275309}}, "System for converting solar heat to electrical energy"</ref> === Prototype in Spain === <!-- a picture is needed, they are available but i do not know how to do it --> In [[1982]], a small-scale experimental model of a solar chimney power plant was built under the direction of German engineer [[Jörg Schlaich]] in [[Manzanares, Ciudad Real]], 150&nbsp;km south of [[Madrid]], [[Spain]]; the project was funded by the German government.<ref>{{cite journal | author=Haaf W, Friedrich K, Mayr G, Schlaich J | title=Solar Chimneys. Part 1: Principle and Construction of the Pilot Plant in Manzanares | journal=International Journal of Solar Energy | volume=2 | issue=1 | year=1983 | pages=3–20}}</ref><ref>{{cite journal | author=Haaf W | title=Solar Chimneys - Part II: Preliminary Test Results from the Manzanares Pilot Plant | journal=International Journal of Solar Energy | volume=2 | issue=2 | year=1984 | pages=141–161}}</ref> The chimney had a height of 195 metres and a diameter of 10 metres, with a collection area (greenhouse) of 46,000&nbsp;m² (about 11 acres, or 244&nbsp;m diameter) obtaining a maximum power output of about 50&nbsp;[[kW]]. However, this was an experimental setup that was not intended for power generation. Instead, different materials were used for testing, such as single or double glazing or plastic (which turned out not to be durable enough) and one section was used as an actual greenhouse, growing plants under the glass. During operation, optimisation data was collected on a second-by-second basis with 180 sensors measuring inside and outside temperature, humidity and wind speed. <ref>Schlaich J, Schiel W (2001), "Solar Chimneys", in RA Meyers (ed), ''Encyclopedia of Physical Science and Technology, 3rd Edition'', Academic Press, London. ISBN 0-12-227410-5 {{PDF|[http://www.solarmillennium.de/pdf/SolarCh.pdf download]|180&nbsp;KB}} </ref> In the choice of materials, it was taken into consideration that such an inefficient but cheap plant would be ideal for third world countries with lots of space - the method is inefficient in land use, but very efficient economically because of the low operating cost. So cheap materials were used on purpose, to see how they would perform, such as a chimney built with iron plating only 1.25 mm thin and held up with [[guy-wire|guy ropes]]. For a commercial plant, a reinforced concrete tower would be a better choice. This pilot power plant operated for approximately eight years, but the chimney guy rods were not protected against corrosion and not expected to last longer than the intended test period of three years. So, not surprisingly, after eight years they had rusted through and broke in a storm, causing the tower to fall over and the plant was decommissioned in 1989. <ref name="Mills">{{cite journal | author=Mills D | title=Advances in solar thermal electricity technology | journal= Solar Energy | volume=76 | issue=1-3 | year=2004 | pages=19–31 | doi=10.1016/S0038-092X(03)00102-6}}</ref> Based on the test results, it was estimated that a 100 MW plant would require a 1000 m tower and a greenhouse of 20 km<sup>2</sup>. Because the costs lie mainly in construction and not in operation (free 'fuel', little maintenance and only 7 personnel), the cost per energy is largely determined by interest rates and years of operation, varying from 5 eurocent per kWh for 4% and 20 years to 15 eurocent per kWh for 12% and 40 years.<ref>"The Solar Chimney" by Jörg Schlaich, 1995</ref> === ''Ciudad Real Torre Solar'' === There is a proposal to construct a solar updraft tower in [[Ciudad Real]], [[Spain]] entitled ''Ciudad Real Torre Solar''. If built, it would be the first of its kind in the [[European Union]]<ref>{{sp icon}} {{cite news |first=J.V. |last=Muñoz-Lacuna |title=Ciudad Real tendrá una torre solar que doblará en alturaa las Torres Gemelas |url=http://www.lasprovincias.es/valencia/pg060213/prensa/noticias/Espana/200602/13/VAL-ESP-051.html |work=lasprovincias.es |date=[[2006-02-13]] |accessdate=2007-03-26}}</ref> and would stand 750 metres tall<ref>{{cite web |url=http://skyscraperpage.com/diagrams/?26629863 |title=Diagrams - SkyscraperPage.com |accessdate=2007-03-27 |year=2007 |work=SkyscraperPage.com}}</ref> – nearly twice as tall as the current tallest structure in the [[European Union|EU]], the [[Belmont transmitting station|Belmont TV Mast]]<ref>{{cite web |url=http://www.aerialsandtv.com/belmonttx.html |title=Belmont Transmitter |accessdate=2007-03-26 |work=A.T.V (Aerials and Television)}}</ref> – covering an area of 350 [[hectare]]s.<ref>{{sp icon}} {{cite news |first=Julio |last=Plaza |title=La Torre Solar |url=http://www.hispalibertas.com/noticias/2006/02/28/la-torre-solar.html |work=HispaLibertas |date=[[2006-02-28]] |accessdate=2007-03-26}}</ref> It is expected to output 40 [[megawatt|MW]] of electricity.<ref>{{sp icon}} {{cite web |url=http://urbanity.blogsome.com/2006/02/13/torre-solar-de-750-metros-en-ciudad-real/ |title=Torre Solar de 750 metros en Ciudad Real |accessdate=2007-03-27 |date=[[2006-02-13]] |work=Urbanity.es}}</ref> === Australian proposal === [[EnviroMission]] has since 2001<ref>{{cite web | last = Davey | first = R | title =New Green energy technology launches | publisher = Australian Securities Exchange | date = [[2001-08-06]] | url = http://www.asx.com.au/asx/statistics/showSignalgDetail.do?issuerId=4715&announcementId=414439 | accessdate = 2007-03-31 }}</ref> proposed to build a solar updraft tower power generating station known as ''Solar Tower Buronga'' at a [http://maps.google.com/?ie=UTF8&ll=-34.036515,142.331228&spn=0.029304,0.057163&t=h&z=14&om=1 location] near [[Buronga, New South Wales]].<ref>{{cite news | last = Woody | first = Todd | coauthors = | title = Tower of Power | work = | pages = | language = | publisher = CNN | date = [[2006-10-02]] | url = http://money.cnn.com/magazines/business2/business2_archive/2006/08/01/8382232/index.htm | accessdate = 2007-03-09 }}</ref> Technical details of the project are difficult to obtain<ref>Diesendorf, Mark (2007). ''Greenhouse Solutions with Sustainable Energy'', UNSW Press, p.176.</ref> and the present status of the project is uncertain.<ref> {{cite news | last = Woody | first = Todd | authorlink = | coauthors = | title = What's Next for the Aussie Solar Tower? | work = | publisher = [http://blogs.business2.com/ Business 2.0 Beta] | date = [[2006-10-26]] | url = http://blogs.business2.com/greenwombat/2006/10/whats_next_for_.html | format = | doi = | accessdate = 2007-03-09 }}</ref> On 18 March 2007, the company board announced a merger with the US-based [[SolarMission Technologies, Inc.]] SolarMission is now the official Solar Tower developer.<ref>{{cite web |url=http://www.solarmissiontechnologies.com/announcements/EVM_CA_Merger_Announcement.pdf |title= Merger to Build Solar Tower Opportunities |accessdate=2007-10-31 |date=2007-03-18 |format=PDF |work=EnvrioMission Ltd. }}</ref> November 1, 2007- Mutual termination of the merger between EnviroMission and SolarMission. They will evaluate the possibility of future alliances when they serve the interests of both parties. == Conversion rate of solar energy to electrical energy == The solar updraft tower does not convert all the incoming solar energy into electrical energy. Many designs in the (high temperature) [[solar thermal]] group of collectors have higher conversion rates. The low conversion rate of the Solar Tower is balanced to some extent by the low investment cost per square metre of solar collection.<ref>{{PDF|[http://www.eere.energy.gov/troughnet/pdfs/status-part1.pdf 3. Solar Energy Systems]|1.24&nbsp;MB}} Status Report on Solar Trough Power Plants (1996)</ref> According to model calculations, a simple updraft power plant with an output of 200&nbsp;MW would need a collector 7 kilometres in diameter (total area of about 38&nbsp;km²) and a 1000-metre-high chimney.<ref name="Schlaich" /> One 200MW 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 38&nbsp;km² collecting area is expected to extract about 0.5 percent, or 5&nbsp;[[W]]/m² of 1&nbsp;[[kW]]/m², of the solar power that falls upon it. Note that in comparison, concentrating thermal [[Concentrated Solar Power#Concentrated solar power (CSP) plants|(CSP)]] or photovoltaic [[Solar cells#Concentrating photovoltaics (CPV)|(CPV)]] solar power plants have an [[Concentrated Solar Power#Conversion rates from solar energy to electrical energy|efficiency ranging from 20-40%]]. Because no data is available to test these models on a large-scale updraft tower there remains uncertainty about the reliability of these calculations.<ref>{{cite journal | author=Pretorius JP, Kröger DG | title=Critical evaluation of solar chimney power plant performance | journal= Solar Energy | volume=80 | issue=5 | year=2006 | pages=535–544 | doi=10.1016/j.solener.2005.04.001}}</ref> The performance of an updraft tower may be degraded by factors such as atmospheric winds,<ref>{{cite journal | author=Serag-Eldin MA | title=Computing flow in a solar chimney plant subject to atmospheric winds | journal=Proceedings of the ASME Heat Transfer/Fluids Engineering Summer Conference 2004 | volume=2 B | year=2004 | pages=1153–1162}}</ref><ref>{{cite journal | author=El-Haroun AA | 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 | year=2002 | pages=9–18 |doi=10.1080/0142591021000003336 | doi_brokendate=2008-06-28}}</ref> by drag induced by bracings used for supporting the chimney,<ref>{{cite journal | author=von Backström TW | title=Calculation of Pressure and Density in Solar Power Plant Chimneys | journal=Journal of Solar Energy Engineering | volume=125 | issue= 1 | year=2003 | pages=127–129 |doi=10.1115/1.1530198}}</ref> and by reflection off the top of the greenhouse canopy. Location is also a factor. A Solar updraft power plant located at high latitudes such as in Canada, only if sloped towards the south, would produce up to 85 per cent of the output of a similar plant located closer to the equator.<ref>{{cite journal | author=Bilgen E, Rheault J | title=Solar chimney power plants for high latitudes | journal= Solar Energy | volume=79 | issue=5 | year=2005 | pages=449–458 |doi=10.1016/j.solener.2005.01.003}}</ref><!-- clearly, by simple geometry, high latitude locations make a considerably larger reduction in output than is implied by the reference! --> ==Related and adapted ideas== * The [[Vortex engine]] proposal replaces the physical chimney by a vortex of twisting air. * ''Floating Solar Chimney Technology'' proposes to keep a lightweight chimney aloft using rings of lifting balloons filled with a lighter-than-air gas. * The chimney could be constructed up a mountainside, using the terrain for support.<ref>{{Cite patent|US|7026723}}, "Air filtering chimney to clean pollution from a city and generate electric power"</ref> * The inverse of the solar updraft tower is the downdraft-driven [[energy tower]]. Evaporation of sprayed water at the top of the tower would cause a downdraft by cooling the air and driving wind turbines at the bottom of the tower. * The SCAF, Solar City Air Filtre, proposes to use the same principle but on a smaller scale with the addition of filters to help clean the air of a city. * It has been proposed to use the greenhouse for food production (except near the tower where the winds would be too strong). == Financial feasibility == This section discusses only the classical design of a Solar updraft tower: more ''exotic variations'' are not considered. A solar updraft power station would require a very large initial capital outlay, which may be offset{{Fact|date=December 2007}}<!-- cite does not mention offset, only gives annuity of 43.7 and operation costs of 2.8 million Euros yieding a LEC of 7 cents per kWh, so any offsetting would appear irrelevant --> by relatively low operating cost.<ref name="Schlaich"/> Like other renewable power sources there would be no cost for fuel. A disadvantage of a solar updraft tower is the much lower conversion efficiency than [[Solar power tower|concentrating solar power stations]] have, thus requiring a larger collector area and leading to higher cost of construction<ref>{{cite journal | last = Trieb | first = Franz | coauthors = Ole Langniß and Helmut Klaiß | title = Solar electricity generation—A comparative view of technologies, costs and environmental impact | journal = Solar Energy | volume = 59 | issue = 1-3 | pages = 89–99 | publisher = Elsevier Science Ltd | date= January-March 1997 | url = http://jgalvez.web.cern.ch/jgalvez/Solar/Articles/TRIE0179.pdf | doi = 10.1016/S0038-092X(97)80946-2 | accessdate = 2007-03-30 }}</ref> and maintenance.<ref name="Mills"/> {{Confusing|date=December 2007}}<!-- what is this trying to say? Which comparisons? Cite them. Which structures are simpler? Is a tower plus collector plus turbines simpler than a freestanding wind rotor? Cite the speculation. --> Financial comparisons between solar updraft towers and concentrating solar technologies contrast a larger, simpler structure against a smaller, more complex structure. The "better" of the two methods is the subject of much speculation and debate. A Solar Tower is expected to have less of a requirement for standby capacity from traditional energy sources than [[wind power]] does. Various types of thermal storage mechanisms (such as a heat-absorbing surface material or salt water ponds) could be incorporated to smooth out power yields over the day/night cycle. Most renewable power systems (wind, solar-electrical) are variable, and a typical national electrical grid requires a combination of base, variable and on-demand power sources for stability. However, since [[distributed generation]] by [[intermittent power sources]] provides "smoothing" of the rate of change, this issue of variability can also be addressed by a large interconnected [http://www.technologyreview.com/Energy/16595/ electrical supergrid], incorporating [[wind farms]], [[hydroelectric]], and [[solar power]] stations.<ref>{{cite web | title = Integration of Wind Energy into the Grid | publisher = European Wind Energy Association - EWEA | date= 2005-2007 | url = http://www.ewea.org/index.php?id=196 | accessdate = 2007-05-29 }}</ref> There is still a great amount of uncertainty and debate on what the cost of production for electricity would be for a solar updraft tower and whether a tower (large or small) can be made profitable. Schlaich et al.<ref name="Schlaich"/> estimate a cost of electricity between 7 (for a 200 MW plant) and 21 (for a 5 MW plant) euro cents per kWh, but other estimates indicate that the electricity cannot possibly be cheaper than 25-35 cents per kWh.<ref>{{note|PhysicaPlus}} {{cite journal | last = Zaslavsky | first = Dan | authorlink = | coauthors = | title = Energy Towers | journal = PhysicaPlus - Online magazine of the Israel Physical Society | volume = | issue = 7 | pages = | publisher = Israel Physical Society | date= 2006 | url = http://physicaplus.org.il/zope/home/en/1124811264/1137833043_en | doi = | id = | accessdate = 2007-03-30 }}</ref> Compare this to LECs of approximately 5 US cents per KWh for a 100 MW plant, wind or natural gas.<ref>[http://www.energy.ca.gov/electricity/levelized_cost.html Levelized Costs of Electricity Production by Technology] California Energy Commission, 2003</ref> No reliable electricity cost figures will exist until such time as actual data are available on a utility scale power plant, since cost predictions for a time scale of 25 years or more are unreliable.<ref>{{cite web | last = Groenendaal | first = B.J. | title = Solar Thermal Power Technologies | work = Monograph in the framework of the VLEEM Project | publisher = Energy research Centre of the Netherlands: ECN | date= July 2002 | url = http://www.ecn.nl/docs/library/report/2002/c02062.pdf | format = PDF | accessdate = 2007-03-30 }}</ref> ==References== {{reflist}} ==External links== *[http://money.cnn.com/2006/08/01/technology/towerofpower0802.biz2/index.htm CNN money article] 2006-10-26 *[http://www.sbp.de Schlaich Bergermann und Partner (SBP)] *[http://www.floatingsolarchimney.gr/ The Floating Solar Chimney Technology] *U.S. Department of Energy's [http://www1.eere.energy.gov/solar/index.html Solar Energy Technologies program] *[http://www.scaf.ch SCAF] *[http://www.greentower.net/UNIVERSITY%20STUDY.htm University of Stellenbosch study] *[http://www.solarmissiontechnologies.com/index.html Solar Mission Technologies] *[http://www.globalwarmingsolutions.co.uk/the_solar_nozzle.htm Solar Nozzle] *{{structurae|id=s0004871|title=Mildura Solar Tower}} *[http://www.enviromission.com.au/SolarTower%20Animation%20Metric.wmv Rendered video of possible tower construction and operation] [[Category:Mildura]] [[Category:Building projects]] [[Category:Buildings and structures in Australia]] [[Category:Power station technology]] [[Category:Solar towers]] [[af:Sonskoorsteen]] [[de:Thermikkraftwerk]] [[es:Torre solar]] [[fr:Tour solaire]] [[he:מגדל שמש]] [[ja:太陽熱発電#ソーラーチムニー]] [[nl:Zonnetoren]] [[pl:Wieża słoneczna]] [[fi:Aurinkotorni]]