View source for Testwiki:Mediation Cabal/Cases/2006-07-12 Solar Updraft Tower/Version1

{{about|Solar Towers and Solar Chimneys and similar [[Solar power]] plants using the convective motion of heated air in a chimney for [[electric power generation]]|various other meanings of the term "Solar Tower", including the astronomical instrument and other uses of the term|solar tower (disambiguation)|the use of solar energy for ventilation|Solar chimney}}

The '''Solar updraft tower''' is a type of [[renewable energy|renewable-energy]] [[power plant]] based on the [[Solar chimney]] concept. Air is heated in a wide [[greenhouse]]; [[convection]] causes the air to rise inside a tall chimney. The moving air spins [[turbines]] that produce [[electricity]].<br>
There are no Solar updraft towers in operation at present. A research [[prototype]] operated in [[Spain]] in the [[1980s]]. 
[[Image:Solar Updraft Tower.png|thumb|right|400px|Schematic of a Solar updraft tower]]
==Description==
The '''Solar updraft tower''' is a proposed kind of [[power station]] that harnesses [[solar energy]] by [[convection]] of heated air within a large [[chimney]]. Inside a very large circular [[greenhouse]] (up to 8 [[kilometer]]s in diameter), air is heated by the sun and travels up a chimney located at its center where it rises naturally, thereby driving [[wind turbine]]s which generate [[electricity]].

Either horizontal axis [[Wind turbine|turbines]] can be installed on the ground in a circle around the foot of the tower as proposed for [[Public utility|utility]]-scale power plants, or (as in the prototype in Spain) a vertical axis turbine at the lower end of the chimney.

Apart from the intensity of the solar radiation the generating [[Power (physics)|capacity]] of a Solar updraft power plant depends 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, while the pressure difference on the ground and therefore updraft increases with chimney height ([[stack effect]]). Therefore, an increase of the collector area and the chimney height both lead to a larger capacity of the power plant. 

The soil underneath the collector stores heat during the day and releases it again during the night, allowing the system to operate for 24 hours a day. Water filled hoses may be placed under the collector to increase heat storage capacity.<ref name="Schlaich">{{cite journal |vauthors=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=[[Portable Document Format|PDF]] |doi=10.1115/1.1823493}}</ref>

===History=== 
In [[1903]], Spanish Colonel Isidoro Cabanyes first proposed a solar chimney power plant in the magazine "La energía eléctrica" <ref>{{cite paper |author=Lorenzo |language=Spanish |url=http://www.fotovoltaica.com/chimenea.pdf |format=[[Portable Document 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}} (Spanish)</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 the USA, <ref>{{cite web |url=http://patft.uspto.gov/netacgi/nph-Parser?Sect2=PTO1&amp;Sect2=HITOFF&amp;p=1&amp;u=%2Fnetahtml%2Fsearch-bool.html&amp;r=1&amp;f=G&amp;l=50&amp;d=PALL&amp;RefSrch=yes&amp;Query=PN%2F4275309 |title= System for converting solar heat to electrical energy |date=1981-06-23 |work=USPTO Patent Full-Text and Image Database |publisher=[[United States Patent and Trademark Office]] }}</ref> Canada,<ref>{{cite web |url=http://patents1.ic.gc.ca/details?patent_number=1023564&amp;language=EN_CA |title=Utilization of Solar Energy |publisher=[[Canadian Intellectual Property Office]] |work=Canadian Patents Database}}</ref> Australia<ref>{{cite web |url=http://v3.espacenet.com/textdoc?DB=EPODOC&IDX=AU499934B&F=0 |publisher=[[European Patent Office]] |work=esp@cenet |title=Apparatus for converting Solar to Electrical Energy |date=1979-05-03}}</ref> and Israel.<ref>{{cite web |url=http://l2.espacenet.com/espacenet/viewer?PN=IL50721&amp;CY=es&amp;LG=en&amp;DB=EPD |publisher=[[European Patent Office]] |work=esp@cenet |title=System and Apparatus for Converting Solar Heat to Electrical Energy |id=IL50721 |date=1979-12-30}}</ref>

===Design===
[[:Image:SolarTower.jpg]]
In [[1982]] a small scale working model of a solar updraft power plant was built in [[Manzanares, Ciudad Real|Manzanares]], [[Ciudad Real]], 150 km south of [[Madrid]] in Spain, under the direction of [[Germany|German]] engineer [[Jörg Schlaich]]. This pilot plant, funded by the German Government,<ref>{{cite journal |vauthors=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> operated for approximately 8 years until 1989. The chimney had a diameter of 10 meters and a height of 195 meters, with a collector (greenhouse) diameter of 244 meters and an area of 46,000 m² (about 11 acres). The power plant achieved a maximum generated electricity output of about 50 [[kW]]. During operation, optimization data was collected on a second-by-second basis;<ref>Schlaich J, Schiel W (2001), "Solar Chimneys", in RA Meyers (ed), ''Encyclopedia of Physical Science and Technology, 3rd Edition'', Academic Press, London. {{ISBN|0122274105}} [http://www.solarmillennium.de/pdf/SolarCh.pdf download] (<small>[[Portable Document Format|PDF]]</small>) </ref> these data are the basis for the design of a utility-scale Solar updraft power plant. 

According to model calculations based upon the data obtained at Manzanares it has been estimated that an updraft power plant with an output of 200 MW would need a collector 7 kilometers in diameter (total area of about 38 km²) and a 1000-meter high chimney.<ref name="Schlaich" /> These model calculations indicate that the solar to electricity conversion efficiency improves with size; therefore, a solar updraft power plant needs to be large for it to be cost-effective. [[EnviroMission]] proposes to construct a 50 [[MW]] power station with a 400 m high chimney for Australia.

Because no data are available to test these models on a large-scale updraft power plant there remains uncertainty about the reliability of these calculations.<ref>{{cite journal |vauthors=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}}</ref> or by drag induced by bracings used for supporting the chimney.<ref name="von Backström">{{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>

===Advantages===
Like other sources of  [[renewable energy]] a Solar updraft power plant would contribute to reducing CO<sub>2</sub> [[greenhouse gas]] emissions by producing sustainable electricity. 

One of the strengths of the Solar updraft power plant is that the system can be configured to operate for 24 hours a day.

A small-scale Solar updraft tower may be an attractive option for remote regions in developing countries.<ref>{{cite journal |vauthors=Onyangoa FN, Ochieng RM | title=The potential of solar chimney for application in rural areas of developing countries | journal= Fuel | volume= | issue= | year= | pages= |doi=10.1016/j.fuel.2006.04.029}}</ref><ref>{{cite journal |vauthors=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 labor to be used for its construction and maintenance.

It has been suggested that a Solar updraft power plant located at high latitudes such as in Canada may produce up to 85% of a similar plant at southern locations.<ref>{{cite journal |vauthors=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>

==Solar to electricity conversion efficiency==
The Solar updraft tower is part of the [[solar thermal]] group of solar conversion technologies. There are several other designs that work in a similar way. The first is the [[Trough concentrator|solar trough]] design and another is the [[Stirling engine|solar dish/stirling]] design. Of these technologies the solar dish/stirling has the highest [[energy efficiency]] (the current record is a conversion efficiency of 30% of solar energy).<ref> {{cite web | url=http://www1.eere.energy.gov/ba/pdfs/solar_overview.pdf | title=Overview of Solar Thermal Technologies | accessdate= 2006-07-26  |format=[[Portable Document Format|PDF]] }} </ref> Solar trough plants have been built with efficiencies of about 20%.

The 50kW Mantazares plant achieved a conversion efficiency of 0.53%, but [[Schlaich Bergermann & Partner|SBP]] believe that this could be increased to 1.3% in a large and improved 100MW unit.<ref>{{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> For comparison, a single solar dish-[[Stirling engine]] installed at [[Sandia National Laboratories]]’ National Solar Thermal Test Facility produces as much as 25 kW, but its footprint is a hundred times smaller than the Mantazares pilot plant. <ref>{{cite press release |url=http://www.sandia.gov/news/resources/releases/2004/renew-energy-batt/Stirling.html |title=Sandia, Stirling to build solar dish engine power plant |date=2004-11-09 |publisher=[[Sandia National Laboratories]] }}</ref> The low efficiency of the Solar Tower is somewhat balanced by the rather low investment cost per m² of [[aperture]]. <ref>{{cite web | publisher=Pilkington Solar International GmbH | url=http://www.eere.energy.gov/troughnet/pdfs/status-part1.pdf | title=3. Solar Energy Systems  Status Report on Solar Trough Power Plants| accessdate= 2006-07-26  |format=[[Portable Document Format|PDF]] }} </ref>

One reason for the low conversion efficiency of the solar updraft tower concept is the relatively small difference in temperature between the highest and lowest temperatures and/or pressure gradients in the system. [[Carnot heat engine#Carnot's theorem|Carnot's theorem]] greatly restricts the efficiency of conversion in these circumstances, with an upper [[Carnot cycle]] [[Carnot cycle#The Carnot cycle 2|extractable efficiency]] of about 15% (assuming <math>T_H</math> ≈ 80°C and <math>T_C</math> ≈ 20°C). Other losses contribute to account for the measured conversion efficiency of 0.53%, such as reflection of light off the top of the canopy, heat loss through the roof of the collector, drag in the chimney,<ref name="von Backström" /> and turbine losses.<ref>{{cite journal |vauthors=Gannon AJ, Von Backström TW | title=Solar chimney turbine performance | journal=Journal of Solar Energy Engineering, Transactions of the ASME | volume=125 | issue= 1 | year=2003 | pages=101-106 | doi=10.1115/1.1530195}}</ref> 

Solar updraft towers would impact a significant area of land to generate as much electricity as is produced by modern power stations using other technology. Because of the low conversion efficiency the proposed Solar updraft power plant in Australia would take a 5x larger area of land than the Solar thermal systems planned for California or Spain to generate the same amount of electrical power. The 500-megawatt (MW) SCE/SES plant planned for California covers 4,500-acres or 18.2 km² (or 36.4 m²/kW) <ref name = "SCE-SES"> {{cite press release | url=http://www.hydrogennow.org/HNews/PressReleases/SCE/SCE-SES-Project.htm | title=Major New Solar Energy Project | publisher=Southern California Edison and Stirling Energy Systems, Inc. | date = 2006-07-26 }} </ref> and the 50MW AndaSol Power Plant that is being built in Spain has a total area of 1.95 km² (39 m²/kW), <ref> {{cite web | url=http://www.solarpaces.org/ANDASOL.HTM | title=2x50MW AndaSol Power Plant Projects in Spain | accessdate = 2006-07-26 }} </ref> as compared to 38 km² for the 200MW Solar Tower design (190 m²/kW).

===Competition===
Over the past several years there has been substantial investments and commitments towards Solar thermal power plants of different design. The [[Solar thermal energy#Concentrated solar power (CSP) plants|Concentrated Solar Power (CSP) Plant]] using the [[Trough concentrator|parabolic trough]] principle called the [[Solar Energy Generating Systems|SEGS]] system, in [[California]] in the [[United States]], <ref> {{cite web | url=http://www.fplenergy.com/portfolio/contents/segs_viii.shtml | accessdate=2006-07-26 | publisher= FLP Energy | title=SEGS III, IV, V, VI, VII, VIII & IX }}</ref> produces 330 MW, and it is currently the largest solar thermal energy system in operation. Furthermore, [[Southern California Edison]] announced an agreement to purchase solar powered [[Stirling engine]]s from [[Stirling Energy Systems]] over a twenty-year period and in quantities (20,000 units) sufficient to generate 500 megawatts of electricity. <ref name = "SCE-SES" /> Stirling Energy Systems announced another agreement with [[Sempra Energy|San Diego Gas & Electric]] to provide between 300 and 900 megawatts of electricity.<ref> {{ cite press release | url = http://www.stirlingenergy.com/breaking_news.htm | accessdate = 2006-07-26 | title = World's Largest Solar Energy Farm to be built in Southern California | publisher = Stirling Energy Systems | date = 2005-10-27 }} </ref>

The largest solar power station in [[Australia]] is the 400 kW array at [[White Cliffs, New South Wales]]. The [[White Cliffs Solar Power Station]] was originally built using solar dish steam boiler technology, but has now been upgraded to photovoltaic to obtain almost twice the electric output from the same dishes. Other significant solar arrays include the 220 kW array on the Anangu Pitjantjatjara Lands in [[South Australia]], the 200 kW array at [[Queen Victoria Market]] in [[Melbourne]] and the 160 kW array at Kogerah Town Square in [[Sydney]]. Numerous smaller arrays have been established, primarily in remote areas where solar power is cost-competitive with diesel power.<ref> {{cite web | url = http://www.ga.gov.au/bin/mapserv40?map=/public/http/www/docs/renewable/ago.map&mode=browse&layer=states&layer=highway&layer=coast&layer=operating&mapext=-2201244.400848+-5190134.542706+2031040.723962+-966224.855040&map_web_template=/public/http/www/docs/renewable/operating/template.html | accessdate = 2006-07-26 | title = Renewable Energy - Power Stations }} </ref>

==Related and adapted ideas==
The [[Vortex engine]] proposal is similar to the solar chimney but replaces the physical chimney by a vortex of twisting air.

Another approach, Floating Solar Chimney Technology,<ref>{{ cite web | url = http://www.floatingsolarchimney.gr/ | title = The innovative Floating Solar Chimney Technology | accessdate = 2006-07-26 }} </ref> proposes to keep a lightweight chimney aloft by lifting balloon rings filled with a lighter than air gas.

Another proposed design would construct the chimney up a mountainside, rather than a freestanding structure in the centre of the solar collector.<ref> {{ cite web | url = http://www.uspto.gov/web/patents/patog/week15/OG/html/1305-2/US07026723-20060411.html | title = Air filtering chimney to clean pollution from a city and generate electric power | accessdate = 2006-07-26 }} </ref>

The inverse of the solar updraft tower is the [[energy tower]], which is driven by spraying water at the top of the tower; evaporation of water causes a downdraft by cooling the air thereby increasing its density, driving wind turbines at the bottom of the tower. This design does not require a large solar collector, but does consume up to 50% of the generated energy operating the water pumps.

==See also==

* [[Active solar]]
* [[Energy conversion]]
* [[Future energy development]]
* [[Passive solar]]
* [[Renewable energy]]
* [[Solar power tower]]
* [[Solar cell]]
* [[Solar chimney]]
* [[Solar panel]]
* [[Solar power]]
* [[Solar thermal energy]]
* [[Solar thermal collector]]
* [[Sustainable energy]]

==References==
<div class="references-small">
<references />
</div>


==External links==
*[http://www.sbp.de Schlaich Bergermann und Partner (SBP)]
*[http://www.enviromission.com.au EnviroMission Limited]
*[http://www.solarmissiontechnologies.com/index.html SolarMission Technologies, Inc.]
*U.S. Department of Energy's [http://www1.eere.energy.gov/solar/index.html Solar Energy Technologies program]
*[http://solarpaces.org SolarPACES]

[[af:Sonskoorsteen]]
[[de:Thermikkraftwerk]]
[[es:Torre solar]]
[[fr:Tour solaire]]
[[nl:Zonnetoren]]
[[fi:Aurinkotorni]]