Solar updraft tower

This article is about a type of power plant. For other uses, see Solar tower (disambiguation).

Schematic presentation of a Solar updraft tower

The solar updraft tower is a renewable-energy power plant. It combines the chimney effect, the greenhouse effect and the wind turbine. Air is heated by sunshine and contained in a very large greenhouse-like structure around the base of a tall chimney, and the resulting convection causes air to rise up the updraft tower. This airflow drives turbines, which produce electricity.

Description

The generating ability of a solar updraft power plant depends primarily on two factors: the collector area and the chimney height. With a larger collector area, a greater volume of air is warmed to flow up the chimney; collector areas as large as 7 kilometres (4.3 mi) in diameter have been considered. With a larger chimney height, the pressure difference increases the stack effect; chimneys as tall as 1,000 metres (3,281 ft) have been considered.

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.^[1]

Turbines can be installed in a ring around the base of the tower, with a horizontal axis, as formerly 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^{[citation needed]} 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.^[1]

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 degraded land.

A small-scale solar updraft tower may be an attractive option for remote regions in developing countries.^[2][3] The relatively low-tech approach could allow local resources and labour to be used for its construction and maintenance.

History

In 1903, Isidoro Cabanyes, a colonel in the Spanish army, proposed a solar chimney power plant in the magazine La energía eléctrica.^[4] One of the next earliest descriptions of a solar chimney power plant was written in 1931 by a German author, Hanns Günther.^[5] Beginning in 1975, Robert E. Lucier applied for patents on a solar chimney electric power generator; between 1978 and 1981 these patents (since expired) were granted in Australia,^[6] Canada,^[7] Israel,^[8] and the USA.^[9]

First Prototype in Spain

SUT as seen from La Solana

SUT powerplant prototype in Manzanares, Spain, seen from a point 8 km to the South

Solar Chimney Manzanares view through the polyester collector roof

Solar Chimney Manzanares-view of the tower through the collector glass roof

View from the tower on the roof with blackened ground below the collector. One can see the different test materials for canopy cover, and 12 large fields of unblackened ground for agricultural test area.

In 1982, a small-scale experimental model of a solar draft tower^[10] was built in Manzanares, Ciudad Real, 150 km south of Madrid, Spain at 39°02′34.45″N 3°15′12.21″W / 39.0429028°N 3.2533917°W / 39.0429028; -3.2533917 (Manzanares Solar Updraft Tower). The power plant operated for approximately eight years. The draft tower's guy-wires, which were not protected against corrosion, failed due to rust and broke in a storm. This caused the tower to fall over. The plant was decommissioned in 1989.^[11]

Inexpensive materials were used in order to evaluate their performance. The solar tower was built of iron plating only 1.25 mm thick under the direction of a German engineer, Jörg Schlaich. The project was funded by the German government.^[12][13]

The chimney had a height of 195 metres and a diameter of 10 metres with a collection area (greenhouse) of 46,000 square metres (11 acres), 244 m diameter, obtaining a maximum power output of about 50 kW. 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 its operation, optimization data was collected on a second-by-second basis with 180 sensors measuring inside and outside temperature, humidity and wind speed.^[14] This was an experimental setup that did not sell energy to produce income.

Jinshawan Updraft Tower

In December 2010, a solar updraft tower in Jinshawan in Inner Mongolia, China started operation, producing 200-kilowatts of electric power.^[15][16] The 1.38 billion RMB (USD 208 million) project was started in May 2009 and its aim is to build a facility covering 277 hectares and producing 27.5 MW by 2013. The greenhouses will also improve the climate by covering moving sand, restraining sandstorms.^[17]

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^[18] and would stand 750 metres tall^[19] – nearly twice as tall as the current tallest structure in the EU, the Belmont TV Mast^[20] – covering an area of 350 hectares (about 865 acres).^[21] It is expected to put out 40 MW of electricity.^[22]

Australian proposal

EnviroMission in 2001,^[23] proposed to build a solar updraft tower power generating station known as Solar Tower Buronga near Buronga, New South Wales.^[24] The company did not complete the project and now plans a similar plant in Arizona. ^[25]

Botswana test facility

Based on the need for plans for long-term energy strategies, Botswana's Ministry of Science and Technology designed and built a small-scale solar chimney system for research. This experiment ran from 7 October to 22 November 2005. It had an inside diameter of 2 m and a height of 22m and was manufactured from glass-reinforced polyester material, with a collection base area of approximately 160 m². The roof was made of a 5 mm thick clear glass that was supported by a steel framework.^[26]

Namibian proposal

In mid 2008, the Namibian government approved a proposal for the construction of a 400 MW solar chimney called the 'Greentower'. The tower is planned to be 1.5 km tall and 280 m in diameter, and the base will consist of a 37 km² greenhouse in which cash crops can be grown.^[27]

Turkish model

A model solar updraft tower was constructed in Turkey as a civil engineering project.^[28] Functionality and outcomes are obscure.^[29][30]

Arizona projects

In October 2010, EnviroMission announced further plans to build two 200 MW Solar Updraft Towers in Western Arizona. Southern California Public Power Authority (SCPPA) has agreed to negotiate a power-purchase agreement with EnviroMission for electricity from its Arizona power plants, should they get built, and the project has been listed by the SCPPA.^[31] As of January 2011, the company has secured $29.8 million in debt and equity from AGS Capital Group.^[32] In August 2011, United States construction services contractor, Hensel Phelps Construction Co. was engaged for delivery of a construction schedule and cost estimate of a 200 MW - producing tower for Enviromission in Arizona.^[33]

Conversion rate of solar energy to electrical energy

The solar updraft tower has power conversion rate considerably lower than many other designs in the (high temperature) solar thermal group of collectors. The low conversion rate of the Solar Tower is balanced to some extent by the low investment cost per square metre of solar collection.^[34]

According to model calculations, it was estimated that a 100 MW plant would require a 1000 m tower and a greenhouse of 20 km². A 200 MW power plant with the same 1000-metre-high tower would need a collector 7 kilometres in diameter (total area of about 38 km²).^[1] 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 km² collecting area is expected to extract about 0.5 percent, or 5 W/m² of 1 kW/m², of the solar power that falls upon it. Note that in comparison, concentrating thermal (CSP) or photovoltaic (CPV) solar power plants have an efficiency ranging between 20% to 31.25% (dish Stirling), although these approaches do not attain 100% utilization of land area which should be considered when contemplating efficiency versus foot print. Because no data is available to test these models on a large-scale updraft tower there remains uncertainty about the reliability of these calculations.^[35]

The performance of an updraft tower may be degraded by factors such as atmospheric winds,^[36][37] by drag induced by the bracings used for supporting the chimney,^[38] and by reflection off the top of the greenhouse canopy.

Using Carnot's theorem, the upper limit of efficiency can be found:

$\eta_{\text{max}} = \eta_{\text{Carnot}} = 1 - \frac{T_C}{T_H}$

For example, if the air entering the base of the tower was 353 K (80 °C; 176 °F) and the surrounding air at the top of the tower was 283 K (10 °C; 50 °F), which matched the exhaust temperature of the tower, then the maximum efficiency would be ~20%. However, if the above 100 MW plant requiring 20 km², and the peak solar radiation falling on the ground was ~1 kWm^-2, the efficiency would be 0.5% as there would be 5 Wm^-2. Thus, 39 units of potentially available energy are consumed for every single unit captured. For perspective, PV panels providing the same amount of energy (assuming they operate at a quite feasible ~20%), would occupy a 40th of the land. Conversely, in the case of the 100 MW system, the same land usage with PV panels could produce 4,000 MW. If the PV panels were operating at the maximum theoretical efficiency of 29%, the power output would be increased to 5800 MW. However, PV panels do not work at night as they have no inbuilt energy storage, perhaps making a tower more suitable for baseline power generation.

It is possible to combine the land use of a solar updraft tower with other uses, in order to make it more cost effective, and in some cases, to increase its total power output. Examples are the positioning of solar collectors or photovoltaics underneath the updraft tower collector. This could be combined with agricultural use.^{[citation needed]}

Mountainside solar draft tower

In 1926 Prof Engineer Bernard Dubos proposed to the French Academy of Sciences the construction of a Solar Aero-Electric Power Plant in North Africa with its solar chimney on the slope of a large mountain.^[39] A mountainside updraft tower can also function as a vertical greenhouse.

Arctic solar draft tower

A Solar updraft power plant located at high latitudes such as in Canada, could produce up to 85 per cent of the output of a similar plant located closer to the equator, but only if the collection area is sloped significantly southward. The sloped collector field is built at suitable mountain hills, which also functions as a chimney. Then a short vertical chimney is added to install the vertical axis air turbine. The results showed that solar chimney power plants at high latitudes may have satisfactory thermal performance.^[40]

Related ideas and adaptations

• 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.^[41]

• The solar chimney could be constructed up a mountainside using inclined terrain for support; this could draw power from the updraft out of a thermal inversion, and improve urban air quality.^[42]

• The atmospheric vortex proposal^[43] replaces the physical chimney by a controlled or 'anchored' cyclonic updraft vortex. Depending on the column gradient of temperature and pressure, or buoyancy, and stability of the vortex, very high-altitude updraft may be achievable. As an alternate to a solar collector, industrial and urban waste-heat could be used to initiate and sustain the updraft in the vortex.

• 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.^[44]

• Release of humid ground-level air from an atmospheric vortex or solar chimney at altitude could form clouds or precipitation, potentially altering local hydrology.^[45][46][47] Local de-desertification, or afforestation could be achieved if a regional water cycle were established and sustained in an otherwise arid area.

• Fitted with a vortex chimney scrubber, the updraft could be cleaned of particulate air pollution. The solar cyclone distiller^[48] could extract atmospheric water by condensation in the updraft of the chimney.

• This solar cyclonic water distiller with a solar collector pond could adapt the solar collector-chimney system for large-scale desalination of collected brine, brackish- or waste-water pooled in the collector base.^[49]

• A form of solar boiler technology placed directly above the turbine at the base of the tower might increase the up-draught.^{[citation needed]}

• If the chimney updraft is an ionized vortex, then the electro-magnetic field could be tapped for electricity, using the airflow and chimney as a generator.^{[citation needed]}

• Energy production and water desalination^[50] could be used to support carbon-fixing or food-producing local agriculture,^[51] and for intensive aquaculture and horticulture under the solar collector as a greenhouse.

Financial feasibility

This section discusses only the simplest, classical design of a solar updraft tower power plant, and variations are not considered.

A solar updraft power station would require a large initial capital outlay, but would have relatively low operating cost.^[1] However, the capital outlay required is roughly the same as next-generation nuclear plants such as the AP-1000 at roughly $5 per W of capacity. Like other renewable power sources there would be no cost for fuel. 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.^[52]

A disadvantage of a solar updraft tower is the much lower conversion efficiency than concentrating solar power stations have, thus requiring a larger collector area and leading to higher cost of construction^[53] and maintenance.^[11]

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.^{[citation needed]}

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 electrical super grid, incorporating wind farms, hydroelectric, and solar power stations.^[54]

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.^[1] 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.^[55] Compare this to LECs of approximately 3 Euro cents per KWh for a 100 MW wind or natural gas plant.^[56] 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.^[57]

See also

• Solar pond

References

1. ^ ^{a b c d e} Schlaich J, Bergermann R, Schiel W, Weinrebe G (2005). "Design of Commercial Solar Updraft Tower Systems—Utilization of Solar Induced Convective Flows for Power Generation" (PDF). Journal of Solar Energy Engineering 127 (1): 117–124. doi:10.1115/1.1823493. http://www.sbp.de/de/html/contact/download/The_Solar_Updraft.pdf. 
2. ^ Onyangoa FN, Ochieng RM (0000). "The potential of solar chimney for application in rural areas of developing countries". Fuel 00 (0): 000–000. doi:10.1016/j.fuel.2006.04.029. 
3. ^ Dai YJ, Huang HB, Wang RZ (2003). "Case study of solar chimney power plants in Northwestern regions of China". Renewable Energy 28 (8): 1295–1304. doi:10.1016/S0960-1481(02)00227-6. 
4. ^ (Spanish) Lorenzo (in Spanish) (PDF). Las chimeneas solares:De una propuesta española en 1903 a la Central de Manzanares. De Los Archivos Históricos De La Energía Solar. http://www.fotovoltaica.com/chimenea.pdf. 
5. ^ Günther, Hanns (1931). In hundert Jahren - Die künftige Energieversorgung der Welt. Stuttgart: Kosmos, Gesellschaft der Naturfreunde. 
6. ^ AU 499934B , "Apparatus for converting Solar to Electrical Energy"
7. ^ CA 1023564 , "Utilization of Solar Energy"
8. ^ IL 50721 , "System and Apparatus for Converting Solar Heat to Electrical Energy"
9. ^ US 4275309 , "System for converting solar heat to electrical energy"
10. ^ "schlaich bergermann und partner". Sbp.de. 2011-08-19. http://www.sbp.de/en#build/show/82-Solar_Chimney_Manzanares. Retrieved 2011-09-11. 
11. ^ ^{a b} Mills D (2004). "Advances in solar thermal electricity technology". Solar Energy 76 (1-3): 19–31. doi:10.1016/S0038-092X(03)00102-6. 
12. ^ Haaf W, Friedrich K, Mayr G, Schlaich J (1983). "Solar Chimneys. Part 1: Principle and Construction of the Pilot Plant in Manzanares". International Journal of Solar Energy 2 (1): 3–20. 
13. ^ Haaf W (1984). "Solar Chimneys - Part II: Preliminary Test Results from the Manzanares Pilot Plant". International Journal of Solar Energy 2 (2): 141–161. 
14. ^ 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 downloadPDF (180 KB)
15. ^ "China's first solar chimney plant starts operating in desert". Gov.cn. 2010-12-28. http://www.gov.cn/english/2010-12/28/content_1773883.htm. Retrieved 2011-09-11. 
16. ^ www.margotweb.net, création sites Internet, développement php - mysql (2010-09-30). "NEW about solar chimney power plants". Solar-chimney.biz. http://www.solar-chimney.biz/new.php?PHPSESSID=160852743538f135a1ef6e9c58c983a4. Retrieved 2011-09-11. 
17. ^ "Xianha: China's first solar chimney plant starts operating in desert". News.xinhuanet.com. 2010-12-27. http://news.xinhuanet.com/english2010/china/2010-12/27/c_13666710.htm. Retrieved 2011-09-11. 
18. ^ (Spanish) Muñoz-Lacuna, J.V. (13 February 2006). "Ciudad Real tendrá una torre solar que doblará en alturaa las Torres Gemelas". lasprovincias.es. http://www.lasprovincias.es/valencia/pg060213/prensa/noticias/Espana/200602/13/VAL-ESP-051.html. Retrieved 26 March 2007. 
19. ^ "Diagrams - SkyscraperPage.com". SkyscraperPage.com. 2007. http://skyscraperpage.com/diagrams/?26629863. Retrieved 27 March 2007. 
20. ^ "Belmont Transmitter". A.T.V (Aerials and Television). http://www.aerialsandtv.com/belmonttx.html. Retrieved 26 March 2007. 
21. ^ (Spanish) Plaza, Julio (28 February 2006). "La Torre Solar". HispaLibertas. Archived from the original on 27 April 2007. http://web.archive.org/web/20070427090637/http://www.hispalibertas.com/noticias/2006/02/28/la-torre-solar.html. Retrieved 26 March 2007. 
22. ^ (Spanish) "Torre Solar de 750 metros en Ciudad Real". Urbanity.es. 13 February 2006. http://urbanity.blogsome.com/2006/02/13/torre-solar-de-750-metros-en-ciudad-real/. Retrieved 27 March 2007. 
23. ^ Davey, R (6 August 2001). "New Green energy technology launches". Australian Securities Exchange. Archived from the original on 26 September 2007. http://web.archive.org/web/20070926225534/http://www.asx.com.au/asx/statistics/showSignalgDetail.do?issuerId=4715&announcementId=414439. Retrieved 31 March 2007. 
24. ^ Woody, Todd (2 October 2006). "Tower of Power". CNN. http://money.cnn.com/magazines/business2/business2_archive/2006/08/01/8382232/index.htm. Retrieved 9 March 2007. 
25. ^ http://www.enviromission.com.au/EVM/Company/ShowPage.aspx/PDFs/1273-76736470/OperationalOverviewJuly1December312010
26. ^ Ketlogetswe, C (21 February 2007). "Solar chimney power generation project—The case for Botswana". Renewable and Sustainable Energy Reviews. http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VMY-4NSWTYP-3&_user=2322062&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_version=1&_urlVersion=0&_userid=2322062&md5=2ef56b9798b0b646b437cc8657203a3b. Retrieved 17 October 2008. 
27. ^ Cloete, R (25 July 2008). "Solar tower sheds light on little-used technology". Engineering News Online. http://www.engineeringnews.co.za/article.php?a_id=137580. Retrieved 17 October 2008. 
28. ^ now to post a comment! (2010-08-21). "solar chimney http://www.unienerji.com". YouTube. http://www.youtube.com/watch?v=-j1K1vwPZS8. Retrieved 2011-09-11. 
29. ^ "Güneş Santrali | Güneş Pili". Unienerji.com. http://www.unienerji.com/?p=310#more-310. Retrieved 2011-09-11. 
30. ^ Koyun A, U¨ c¸gu¨ l I, Acar M, S¸enol R. Gu¨ nes¸ Bacası Sisteminin Termal O¨ zet Dizaynı. Tesisat Mu¨ hendislig˘i Dergisi 2007;98:45-50. available at: http:// www.mmoistanbul.org/yayin/tesisat/98/6.
31. ^ "::: Southern California Public Power Authority ::::::::::". Scppa.org. 2010-10-21. http://www.scppa.org/pages/projects/lapaz_solartower.html. Retrieved 2011-09-11. 
32. ^ "EnviroMission Wins $29.8M in Debt/Equity for Solar Updraft Tower". Greentechmedia.com. http://www.greentechmedia.com/articles/read/enviromission-secures-30m-hybrid-debt-equity-facility/. Retrieved 2011-09-11. 
33. ^ http://www.enviromission.com.au/irm/Company/ShowPage.aspx/PDFs/1299-82348792/HenselPhelpsAppointedUSSolarTowerContractor
34. ^ 3. Solar Energy SystemsPDF (1.24 MB) Status Report on Solar Trough Power Plants (1996)
35. ^ Pretorius JP, Kröger DG (2006). "Critical evaluation of solar chimney power plant performance". Solar Energy 80 (5): 535–544. doi:10.1016/j.solener.2005.04.001. 
36. ^ Serag-Eldin MA (2004). "Computing flow in a solar chimney plant subject to atmospheric winds". Proceedings of the ASME Heat Transfer/Fluids Engineering Summer Conference 2004. 2 B: 1153–1162. 
37. ^ El-Haroun AA (2002). "The effect of wind speed at the top of the tower on the performance and energy generated from thermosyphon solar turbine". International Journal of Solar Energy 22 (1): 9–18. doi:10.1080/01425910212851. 
38. ^ von Backström TW (2003). "Calculation of Pressure and Density in Solar Power Plant Chimneys". Journal of Solar Energy Engineering 125 (1): 127–129. doi:10.1115/1.1530198. 
39. ^ http://www.intechopen.com/download/pdf/pdfs_id/8557
40. ^ Bilgen E, Rheault J (2005). "Solar chimney power plants for high latitudes". Solar Energy 79 (5): 449–458. doi:10.1016/j.solener.2005.01.003. 
41. ^ "Solar Energy : A multi-stage down-draft evaporative cool tower for semi-enclosed spaces: Experiments with a water spraying system". ScienceDirect. http://www.sciencedirect.com/science/article/pii/S0038092X07002423. Retrieved 2011-09-11. 
42. ^ US 7026723 , "Air filtering chimney to clean pollution from a city and generate electric power"
43. ^ "Atmospheric Vortex Engine". Vortexengine.ca. http://vortexengine.ca/index.shtml. Retrieved 2011-09-11. 
44. ^ "Solar pond tower for 5 €ct/kWh". GreenIdeaLive. http://www.greenidealive.org/110599/466/solar-pond-tower-for-5-ct/kwh.html. Retrieved 2011-09-11. 
45. ^ Zhou et al. Numerical investigation of a plume from a power generating solar chimney in an atmospheric cross flow. Atmospheric Research 91 (2009) 26–35
46. ^ Atmospheric Environment 18 (1984) 11:2483-9
47. ^ J. Sol. Energy Eng. / Volume 131 / Issue 1. Cloud Formation in the Plumes of Solar Chimney Power Generation Facilities: A Modeling Study J. Sol. Energy Eng. -- February 2009 -- Volume 131, Issue 1, 011009 doi:10.1115/1.3028041
48. ^ Kashiwa BA,Kashiwa CB; Kashiwa, C (2008). "The solar cyclone: A solar chimney for harvesting atmospheric water". Energy 33 (2): 331–339. doi:10.1016/j.energy.2007.06.003. 
49. ^ Zhou et al. Comparison of classical solar chimney power system and combined solar chimney system for power generation and seawater desalination. Desalination 250 (2010) 249–256
50. ^ Desalination 250 (2010) 249-256
51. ^ Tom Bosschaert (2008-09-26). "Solar Updraft Tower Research: Except Consulting". Except.nl. http://www.except.nl/consult/SolarUpdraftTower/solar_updraft_research.html. Retrieved 2011-09-11. 
52. ^ "The Solar Chimney" by Jörg Schlaich, 1995
53. ^ Trieb, Franz; Ole Langniß and Helmut Klaiß (January 1997). "Solar electricity generation—A comparative view of technologies, costs and environmental impact" (PDF). Solar Energy (Elsevier Science Ltd) 59 (1-3): 89–99. doi:10.1016/S0038-092X(97)80946-2. Archived from the original on 15 June 2007. http://web.archive.org/web/20070615183951/http://jgalvez.web.cern.ch/jgalvez/Solar/Articles/TRIE0179.pdf. Retrieved 30 March 2007. 
54. ^ "Integration of Wind Energy into the Grid". European Wind Energy Association - EWEA. 2005-2007. http://www.ewea.org/index.php?id=196. Retrieved 29 May 2007. 
55. ^ ^ Zaslavsky, Dan (2006). "Energy Towers". PhysicaPlus - Online magazine of the Israel Physical Society (Israel Physical Society) (7). http://physicaplus.org.il/zope/home/en/1124811264/1137833043_en. Retrieved 30 March 2007. 
56. ^ Levelized Costs of Electricity Production by Technology California Energy Commission, 2003
57. ^ Groenendaal, B.J. (July 2002). "Solar Thermal Power Technologies" (PDF). Monograph in the framework of the VLEEM Project. Energy research Centre of the Netherlands: ECN. http://www.ecn.nl/docs/library/report/2002/c02062.pdf. Retrieved 30 March 2007. 

External links

• video link Spanish solar updraft tower
• video link Austrailian tower proposal
• video link Solar Updraft Tower - a small model with various substrates
• The Floating Solar Chimney Technology
• Solar Nozzle
• CNN money article 2006-10-26
• Mildura Solar Tower at Structurae
• SCAF
• Schlaich Bergermann und Partner (SBP)
• University of Stellenbosch study
• U.S. Department of Energy's Solar Energy Technologies program
• Atmospheric Vortex alternative to Solar Chimney
• 2nd International Conference on Solar Chimney Power Technology