Solar chimney

From Academic Kids

A solar chimney is an apparatus for harnessing solar energy by convection of heated air.

In its simplest form, it simply consists of a black-painted chimney. During the daytime, solar energy heats the chimney and thereby heats the air within it, resulting in an updraft of air within the chimney. The suction this creates at the chimney base can be used to ventilate, and thereby cool, the building below. In most parts of the world, it is easier to harness wind power for such ventilation, but on hot windless days such a chimney can provide ventilation where there would otherwise be none.

Missing image
Solartower_tr01.png
General concept of proposed solar chimney power station

This principle has been proposed for electric power generation, using a large greenhouse at the base rather than relying on heating of the chimney itself. The main problem with this approach 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.

Contents

Power station designs

History

One of the earliest descriptions of a solar chimney power station was written in 1931 by a German author, Hanns Günther.

More recently Schlaich, Bergerman and Partner, under the direction of German engineer Prof. Dr. Ing. Jörg Schlaich, built a working model of a solar tower in 1982 in Manzaranes, (Spain), 150 km south of Madrid, which was funded by the German Government. This power plant operated successfully for approximately 8 years. The chimney had a diameter of 10 metres and a height of 195 metres, and the maximum power output was about 50 kW.

It was destroyed by heavy weather and thunderstorms in 1989 and was officially decommissioned. However, during the final 3 years, optimization data was collected on a second-by-second basis. This data has been licensed to EnviroMission and SolarMission Technologies Inc. USA, who plan to manufacture solar chimneys under the brand name Solar Tower. At the beginning of 2005 they started collecting meteorological data at a proposed site in New South Wales, Australia, and hope to build the tower and begin full operation in 2008.

The maximum power output for this tower is expected to be 200 MW. The proposed chimney was originally to be 1km high, and the base 3.5km in diameter. However, reports now indicate that due to improved heat absorbtion materials being used for the base, the tower height and base diameter will be substantially reduced by an unknown amount by the time production is completed.

No patent was ever awarded for the technology, and so similar solar chimneys may be built at anytime, anywhere by anyone so long as local laws and official regulations are observed in the respective jurisdictions.

Byproducts

The most significant byproducts from proposed designs are distilled water (made from ocean water or ground water) and in some designs produce is grown under the solar collector.

For these designs Fruits and vegetables, as well as medicinal and aromatic essential oils made from herbs and flowers, seaweeds and planktons, blue-green algae, have all been suggested as suitable crops for these scenarios. Residual biomass might also create additional heat during composting, as could the various distillation, food processing and manufacturing operations. Other byproducts may include ethanol and methane, biodiesel and all manner of vegetable and plant derivatives.

It is also suggested that heat produced from the air-conditioning of nearby factories, offices, schools, shopping malls and homes could be funneled to the tower to optimize refrigeration and air-conditioning operations. Thermodynamically, this must of course reduce the power available for power generation at the tower.

Reliability

Another benefit of the solar tower concept is its ability to generate surrogate solar power during cloudy periods and at night. Water vapors rising through the tower during daylight hours are condensed near the top of the solar tower and return to holding tanks situated throughout the structure. The distributed water vessels act collectively as a heat sink. The radiant heat, escaping from the water containers during overcast or cooling periods and at night, continues to drive the turbines. Near dawn, the cooled waters, driven by gravitational pull, return towards the periphery, driving hydroelectric turbines, and perform other kinetic works. Thereafter, the cooled waters may be distributed as irrigation for the tower's gardens, tree farms, reforestation projects and as domestic drinking water. Robustness from storms could be greatly improved by running the chimney up a steep mountain side instead of free standing.

Comparisons

If Solar chimneys are to replace conventional sources of electricity production in NSW, then quite a number have to be built. Consider the following statistics:

  • The Coal-fired power station near Lithgow - Wallerawang - produces 1000 MW of electrical power.[1] (http://www.de.com.au/Online/Default.asp?DeptID=191)
  • The Coal-fired power station on Lake Macquarie - Vales Point - produces 1320 MW of electrical power. [2] (http://www.de.com.au/Online/Default.asp?DeptID=192)
  • The Coal-fired power station near Mudgee - Mount Piper - produces 1320 MW of Electrical power.[3] (http://www.de.com.au/Online/Default.asp?DeptID=190)
  • The Coal-fired power station on Lake Macquarie - Munmorah - produces 1400 MW of Electrical Power.[4] (http://www.skmconsulting.com/pagetemplates/content/popup.cfm?id=840)
  • The Coal-fired power station near Muswellbrook - Liddell - produces 2000 MW of electrical power.[5] (http://www.macgen.com.au/about_us/liddell.htm)
  • The Coal-fired power station on Lake Macquarie - Eraring - produces 2640 MW of electrical power.[6] (http://www.deh.gov.au/industry/corporate/eecp/case-studies/eraring.html)
  • The Coal-fired power station near Muswellbrook - Bayswater - produces 2640 MW of electrical power.[7] (http://www.macgen.com.au/about_us/bayswater.htm)
  • The Hydro-electric power stations in the Snowy Mountains produce 3756 MW of electrical power.[8] (http://www.snowyhydro.com.au/levelTwo.asp?pageID=244&parentID=242)

In order for the seven coal-fired power stations above to be replaced, 62 Solar chimneys must be built (assuming 200 MW each). This does not include other, smaller power stations throughout NSW, nor the rest of Australia.

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