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Removed promotional EnviroMission and SolarMission content. Press releases by companies do not make valid encyclopedia content.
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In [[1982]], a medium-scale working model of a solar chimney power plant was built under the direction of German engineer [[Jörg Schlaich]] in [[Solar Tower Manzanares|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]]. During operation, optimisation 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 0-12-227410-5 {{PDF|[http://www.solarmillennium.de/pdf/SolarCh.pdf download]|180&nbsp;[[Kibibyte|KiB]]<!-- application/pdf, 185005 bytes -->}} </ref> This pilot power plant operated successfully for approximately eight years and was decommissioned in 1989. The tower was featured on the [[Australian]] television program [[Beyond 2000]] in 1984, with the premise of its adapability to the Australian [[Outback]] for power production without intereference with animal pastoral agriculture.
In [[1982]], a medium-scale working model of a solar chimney power plant was built under the direction of German engineer [[Jörg Schlaich]] in [[Solar Tower Manzanares|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]]. During operation, optimisation 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 0-12-227410-5 {{PDF|[http://www.solarmillennium.de/pdf/SolarCh.pdf download]|180&nbsp;[[Kibibyte|KiB]]<!-- application/pdf, 185005 bytes -->}} </ref> This pilot power plant operated successfully for approximately eight years and was decommissioned in 1989. The tower was featured on the [[Australian]] television program [[Beyond 2000]] in 1984, with the premise of its adapability to the Australian [[Outback]] for power production without intereference with animal pastoral agriculture.


== Proposed solar tower projects ==
[[Image:SolarTower.jpg|thumb|right|Artist's impression of Solar Tower. Note the scale of the tower compared to the road.]]
Proposals have been made for Australia, China,<ref>{{cite news |url=http://www.atimes.com/atimes/China/FJ07Ad03.html |title=China invests in solar towers |accessdate=2006-07-09 |publisher=[[Asia Times]] |date=[[2004-10-07]]}}</ref> the USA,<ref>{{cite web |publisher=Scan Systems |url=http://www.scansystems.com/news.php?id=4&newsid=72 Monohans Solar Tower Project|title=Heart of oil industry could become site of renewable energy project |date=[[2003-07-19]] }}</ref> and Spain<ref>[http://www.astroseti.org/vernew.php?codigo=2188 Torre solar de 750 metros de altura en Ciudad Real (España)]</ref>.



A similiar tower has been proposed for construction in the [[Karoo]] desert in South Africa.


== Financial feasibility ==
== Financial feasibility ==
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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 thus whether a tower (large or small) can be made profitable.
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 thus whether a tower (large or small) can be made profitable.

It was claimed, in 2002, that a Solar Tower in Australia would be an expensive way of generating electricity as compared to a conventional [[wind farm]].<ref> {{cite news |url=http://www.guardian.co.uk/international/story/0,3604,776735,00.html |title=Real power from nothing but hot air|accessdate=2006-07-09 |work=[[The Guardian]] |author=David Fickling |date=[[2002-08-19]]}}</ref>

However, a 2006 study claims that a large tower in the southwestern [[United States]] could not only outperform windfarms on a cost basis but also compete directly with current conventional gas-fired, and some coal-fired, plants.<ref>{{cite web |url=http://www.watervilleresearch.com/companies/special/273-3.html |title=EnviroMission, Ltd.: Performance and Financial Projections |publisher=Waterville Investment Research |accessdate=2006-07-09}}</ref>.


No reliable electricity cost figures are expected until such time as engineering models are available for finalised tower designs and construction has begun on a production tower.
No reliable electricity cost figures are expected until such time as engineering models are available for finalised tower designs and construction has begun on a production tower.

Revision as of 00:14, 9 March 2007

Schematic 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 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.

There are no solar updraft towers in operation at present. 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.[1]

Turbines can be installed in a ring around the base of the tower, with a horizontal axis, as planned for the Australian project described below and seen in the diagram above; or—as in the prototype in Spain—a single vertical axis turbine can be installed inside the chimney.

Solar towers do not produce carbon dioxide emissions during their operation, but are associated with the manufacture of its construction materials, particularly cement. Net energy payback is estimated to be 2-3 years.Cite error: A <ref> tag is missing the closing </ref> (see the help page).[2] 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".[3] 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 patents on a solar chimney electric power generator; between 1978 and 1981 these patents, since expired, were granted in Australia[4], Canada,[5], Israel.[6] and the USA.[7]

Prototype

In 1982, a medium-scale working model of a solar chimney power plant was built under the direction of German engineer Jörg Schlaich in Manzanares, Ciudad Real, 150 km south of Madrid, Spain; the project was funded by the German government.[8][9] The chimney had a height of 195 metres and a diameter of 10 metres, with a collection area (greenhouse) of 46,000 m² (about 11 acres, or 244 m diameter) obtaining a maximum power output of about 50 kW. During operation, optimisation data was collected on a second-by-second basis.[10] This pilot power plant operated successfully for approximately eight years and was decommissioned in 1989. The tower was featured on the Australian television program Beyond 2000 in 1984, with the premise of its adapability to the Australian Outback for power production without intereference with animal pastoral agriculture.


Financial feasibility

With a very large initial capital outlay, no costs for consumables (i.e. fuel) and relatively constant income (from electricity sales) over the life of the project, a solar updraft tower would be placed in the same asset class as dams, bridges, tunnels, motorways and other similar large infrastructure projects. Financial viability would be assessed on a similar basis.[11]


Unlike a wind farm[12] a Solar Tower is not expected to create a reliance on standby capacity from traditional energy sources.

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 and potentially allow a solar updraft tower to provide something similar to base load power. This is highly desirable, as 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.

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 thus whether a tower (large or small) can be made profitable.

No reliable electricity cost figures are expected until such time as engineering models are available for finalised tower designs and construction has begun on a production tower.

Given the novelty and enormous scale of any commercial solar updraft tower project, tourism income may become a factor, particular for the first towers to be created. Some promotion videos for the Enviromission tower have even shown a glass observation area at the top of the tower.

Given that towers would likely be built in poorer areas with very low-value land, this may be more of interest to the local government than to the operator itself.

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 solar thermal group of collectors have higher conversion rates. The low conversion rate of the Solar Tower is balanced by the low investment cost per square metre of solar collection.[13]

According to model calculations, a simple updraft power plant with an output of 200 MW would need a collector 7 kilometres in diameter (total area of about 38 km²) and a 1000-metre-high chimney.[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 per cent, or 5 W/m² of 1 kW/m², of the solar power that falls upon it. Note that in comparison, biomass photosynthesis is about 0.1 per cent efficient. Because no data is available to test these models on a large-scale updraft tower there remains uncertainty about the reliability of these calculations.[14].

The performance of an updraft tower may be degraded by factors such as atmospheric winds,[15][16] or by drag induced by bracings used for supporting the chimney.[17] Another inefficiency is that reflection of light off the top of the canopy implies a loss of 7.7 per cent of incoming solar energy, as calculated by the fresnel equations, if the canopy is made of common glass.

Location is also a factor. A Solar updraft power plant located at high latitudes such as in Canada may produce no more than 85 per cent of a similar plant located closer to the equator.[18]

  • 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. [19]
  • 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. This design does not require a large solar collector but does consume up to 50 per cent of the generated energy operating the water pumps.

See also

References

  1. ^ a b 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.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  2. ^ 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.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  3. ^ Lorenzo. "Las chimeneas solares:De una propuesta española en 1903 a la Central de Manzanares" (pdf) (in Spanish). De Los Archivos Históricos De La Energía Solar. {{cite journal}}: Cite journal requires |journal= (help) (Spanish)
  4. ^ AU 499934B , "Apparatus for converting Solar to Electrical Energy"
  5. ^ CA 1023564 , "Utilization of Solar Energy"
  6. ^ IL 50721 , "System and Apparatus for Converting Solar Heat to Electrical Energy"
  7. ^ US 4275309 , "System for converting solar heat to electrical energy"
  8. ^ 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.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  9. ^ Haaf W (1984). "Solar Chimneys - Part II: Preliminary Test Results from the Manzanares Pilot Plant". International Journal of Solar Energy. 2 (2): 141–161.
  10. ^ 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 Template:PDF
  11. ^ Jörg Schlaich, Rudolf Bergermann, Wolfgang Schiel, Gerhard Weinrebe. "Design of Commercial Solar Updraft Tower Systems – Utilization of Solar Induced Convective Flows for Power Generation" (pdf). Schlaich Bergermann und Partner (sbp gmbh). Retrieved 2006-11-28. {{cite journal}}: Cite journal requires |journal= (help)CS1 maint: multiple names: authors list (link)
  12. ^ Strong, Geoff (10 August 2006). "More puff than power". The Age. Retrieved 2006-11-27. {{cite news}}: Cite has empty unknown parameter: |coauthors= (help)
  13. ^ Template:PDF Status Report on Solar Trough Power Plants (1996)
  14. ^ 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
  15. ^ 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.
  16. ^ 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:10.1080/0142591021000003336
  17. ^ 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
  18. ^ 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
  19. ^ US 7026723 , "Air filtering chimney to clean pollution from a city and generate electric power"

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