Misplaced Pages

Solar updraft tower

Article snapshot taken from Wikipedia with creative commons attribution-sharealike license. Give it a read and then ask your questions in the chat. We can research this topic together.

This is an old revision of this page, as edited by Zzzzzzzzzzz (talk | contribs) at 03:41, 7 July 2006. The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

Revision as of 03:41, 7 July 2006 by Zzzzzzzzzzz (talk | contribs)(diff) ← Previous revision | Latest revision (diff) | Newer revision → (diff)
This article may require copy editing for grammar, style, cohesion, tone, or spelling. You can assist by editing it. (Learn how and when to remove this message)
This article is 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. For various other meanings of the term "Solar Tower", including the astronomical instrument and other uses of the term, see solar tower (disambiguation). For the use of solar energy for ventilation, see Solar chimney.

The Solar updraft tower is a type of renewable-energy power plant based on the Solar chimney concept. There are presently no solar updraft towers. One was built in Spain, but has been decomissioned, and another is planned for Australia, but construction has not yet started.

Schematic of a Solar updraft tower

Background

The Solar updraft tower is a proposed kind of power station that harnesses solar energy by convection of heated air within a large chimney. For electric power generation a large greenhouse is used at the base rather than relying on heating of the chimney itself.

In 1903, Spanish Colonel Isidoro Cabanyes first proposed a solar chimney power plant in the magazine "La energía eléctrica" . 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 the USA, Canada, Australia and Israel.

In 1982 a small scale working model of a solar chimney was built under the direction of German engineer Jörg Schlaich in Manzanares, 150 km south of Madrid in Spain; the project was funded by the German Government. This pilot power plant operated successfully for approximately 8 years and was decommissioned in 1989. The chimney had a diameter of 10 metres and a height of 195 metres, with a collection area (greenhouse) of 46,000 m² (about 11 acres) obtaining a maximum power output of about 50 kW. During operation, optimization data was collected on a second-by-second basis.

Description

The technology is relatively simple. Inside a very large circular greenhouse (between 2 and 30 kilometres in diameter), air is heated by the sun and travels up a convection tower where it rises naturally, thereby driving wind turbines which generate electricity.

Either horizontal axis turbines can be installed on the ground in a circle around the foot of the tower as planned for the Australian project described below, or (as in Spain) a vertical axis turbine at the lower end of the chimney (see schematic).

Apart from the intensity of the solar radiation the generating 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 air is warmed up and flows 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 small test facility in Manzanares consistently generated 50 kW; it is this solar updraft tower which is the basis for the technology. This pilot plant had a collector diameter of 244 metres and a chimney height of 195 metres, and achieved an output of 50 kilowatts. 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.

The main problem with the solar updraft tower concept is the relatively small difference in temperature between the highest and lowest temperatures in the system. Carnot's theorem greatly restricts the efficiency of conversion in these circumstances. A solar updraft power plant needs to be large for it to be competitive, because yield increases with size, and therefore requires high investments upfront. An updraft power plant with an output of 200 MW would need a collector area 7 kilometres in diameter and a 1000 metre high chimney.

Solar Tower Buronga

File:SolarTower.jpg
Artist's impression of Solar Tower

EnviroMission has been planning to build a solar updraft tower, called the Solar Tower Buronga, at Buronga in Wentworth Shire in south-western New South Wales, Australia. The originally-announced design called for a 200 megawatt tower at a height of 1 km and costing around AU$900 million. At the beginning of 2005 they started collecting meteorological data at the proposed site north of Mildura, Australia, with the intent to have a fully operational Solar Tower power station in 2008.

The maximum power output of the original concept of the Solar Tower Buronga was 200 MW. The proposed solar chimney was originally to be 1 km high, and the collector area 7 km in diameter (total area of about 38 km²). From those numbers it appears that the solar chimney would extract about 0.5% of the solar power (1 kW/m²) that falls on the area it covers.

However, the scale was recently reduced to only a 50 MW tower with a height of 650 m. This would be the minimum size and the most risk-averse option in what the company announced as a "flexibly scalable" 50-200 MW range that can be scaled to local and nearby demand. The status of these plans remains unclear.

EnviroMission has also been working with Sunshine Energy (Aust.) Pty Ltd. who made an initial USD$8,000,000 investment to enable development of this technology in China, and a third Solar Tower was reputedly to be built in Texas although few details are available.

Evaluation

The Solar updraft tower is part of the solar thermal group of solar conversion technologies. There are two other designs that work in a similar way. The first is the solar trough design and the other is the 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). Solar trough plants have been built with efficiencies of about 20%. The 500-megawatt (MW) SCE/SES plant would extract about 2.75% of the solar power (1 kW/m²) that impinges on its 4,500-acres (18.2 km²).. However, due to its greater scale and simplicity, the solar chimney may have an economic efficiency approaching or exceeding that of the other methods.

For comparison, the Concentrated Solar Power (CSP) Plant using the parabolic trough principle called the SEGS system, in California in the United States, 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 engines from Stirling Energy Systems over a twenty year period and in quantities (20,000 units) sufficient to generate 500 megawatts of electricity. Stirling Energy Systems announced another agreement with San Diego Gas & Electric to provide between 300 and 900 megawatts of electricity.

Given that a solar updraft tower is "mostly concrete with a few moving parts" and does not have a lot of mechanical complexity, it is considered to be economically attractive. Solar updraft towers will contribute to reducing greenhouse gas emissions by producing sustainable electricity. To replace a typical 2000 MW black coal-fired power station, about 10 solar chimneys of the capacity of the originally proposed test plant would need to be built (depending on scale and capacity). This would also abate more than 14 million tonnes of greenhouse gases from entering the atmosphere annually.

So an area of 380 km² (this is about the size of the Isle of Wight) would be required to replace one coal-fired power station. To replace all 28,000 MW of coal-fired electricity generating capacity in Australia a total of 140 solar updraft towers would have to be built, and 5320 km² covered under glass; an area 50% larger than Long Island or Majorca. This makes this technology useful only for some countries and lands, with large desert areas.

Competition

The Vortex engine, proposed by Louis Michaud, is an idea very similar to the solar chimney but replacing the physical chimney by a vortex of twisting air. However it is not absolutely clear that this could be made workable (for instance, wind might disrupt the vortex).

An alternative of the solar updraft tower is the energy tower proposed by Dan Zaslavsky. The "energy tower" 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 windturbines at the bottom of the tower. The "energy tower" requires a hot arid climate, and large quantities of water. Saline seawater may be used for this purpose, since fresh water is a scarce commodity in arid areas. Though significant amount of energy (about 40-50% of the windturbine generated output) is consumed by pumping the liquid water to the top, the major advantage of this downdraft scheme is that it avoids large area solar collectors needed to drive an updraft tower. Dry air is continuously sucked into the tower at the top, without need for a large area collector.

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, mainly in remote areas where solar power is cost-competitive with diesel power.

See also

References

  1. 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)
  2. "System for converting solar heat to electrical energy". USPTO Patent Full-Text and Image Database. United States Patent and Trademark Office. 1981-06-23. {{cite web}}: Check date values in: |date= (help)
  3. "Utilization of Solar Energy". Canadian Patents Database. Canadian Intellectual Property Office.
  4. "Apparatus for converting Solar to Electrical Energy". esp@cenet. European Patent Office. 1979-05-03. {{cite web}}: Check date values in: |date= (help)
  5. "System and Apparatus for Converting Solar Heat to Electrical Energy". esp@cenet. European Patent Office. 1979-12-30. IL50721. {{cite web}}: Check date values in: |date= (help)
  6. "Sandia, Stirling to build solar dish engine power plant" (Press release). Sandia National Laboratories. 2004-11-09. {{cite press release}}: Check date values in: |date= (help)
  7. Jörg Schlaich, Rudolf Bergermann, Wolfgang Schiel, Gerhard Weinrebe Design of Commercial Solar Updraft Tower Systems – Utilization of Solar Induced Convective Flows for Power Generation page 7, table 2
  8. http://www.abc.net.au/news/items/200606/1661417.htm?victoria
  9. Major New Solar Energy Project Announced By Southern California Edison and Stirling Energy Systems, Inc., press release
  10. http://www.fplenergy.com/portfolio/contents/segs_viii.shtml
  11. http://pesn.com/2005/08/11/9600147_Edison_Stirling_largest_solar/
  12. http://www.stirlingenergy.com/breaking_news.htm
  13. http://www.sustainabilitycentre.com.au/WindPowersStrength.pdf
  14. http://www.consortia.org.il/ConSolar/Sabin/Zas/Zas4.html
  15. 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 AGO - Renewable Energy - Power Stations

External links

Template:Sustainability and energy development group

Categories: