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Solar Chimney Tower Plant


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¡°Hot air rises.¡± This is the most basic fact employed in the design of the gigantic solar chimney tower plant. The spread-out solar collectors receive the sunlight and act like a greenhouse together with the ground. Air in the ¡°greenhouse¡± is heated and pushed toward the turbines at the bottom of the chimney at speeds of up to 70km/h (43.5 mi/h). The buoyancy effect created by the pressure difference from the air under the collectors and ambient (surrounding/outside) air produces a driving force to make sure the air moves fast.
The size of the collector and area and the height of the chimney decide the capacity of the electricity production. The larger the collecting area, the more air flow and heat it traps; the higher the height of the chimney, the greater the pressure difference. This is called the stack effect in physics.


Heat Can Be Stored by the Ground. The ground beneath the collector roof absorbs the heat and re-radiates it during the night, therefore able to provide energy 24 hours a day. Other uses for the space in between the roof and ground have been proposed, such as dehydration of fruits or vegetables.



Principle of thermal energy storage with water-filled black tubes for additional thermal storage capacity. This works better than soil alone as water as water¡¯s heat capacity is five times larger than that of soil. Also heat transfer between water tubes and water is much higher than that between ground surface and the soil layers underneath. (Schlaich, J. et al )

 


 

The First Prototype Plant was established in Manzanares, Spain in 1981, jointly invested by German government and a Spanish Utility . The chimney is 194.8 meter (639.1 ft) in height and 10 meter(32.8 ft) in diameter ; collector zone(greenhouse) of 244m(800.5ft) in diameter. It produced an upwind velocity of 15 m/s(33.5mi/h), reaching a total output of 50 KW. It was set up mainly for experimental use to test different materials and other parameters. One sections of the collector zone is actually used as a greenhouse to grow plants. Here is video clips of the plant:

 

 



A Future Plant In 2002, an Australian company EnviroMission acquired the permission from the government to build a 1000 m high by 7 km diameter solar chimney plant. A power output of 200 MW is expected. The greenhouse will use heat enhancing properties materials including glass, polycarbonate and polymer while the chimney will just be forged with reinforced concrete. It will prevent over 900,000 tons of greenhouse gases otherwise to be created by fossil fuel plants.
In Terms Of Conversion Efficiency, the Australian SCPP project estimated that they can utilize about 0.5 percent, or 5 W/m2 of 1 KW/m2, of the solar radiation the sun pours onto the whole collecting area. It is a rather low conversion rate considering the 15%-30% of other concentrated solar power technologies (PTPP and Parabolic dish respectively). But the reliability of these calculations remains to be further investigated because of insufficient testing data.


Click here for an animation of what it looks like!
http://www.enviromission.com.au/SolarTower%20Animation%20Metric.wmv

 



The Bulk of the Cost of a SCPP falls on the initial construction of the plants. It involves relatively less sophisticated technologies and therefore very ideal for less developed countries with optimal solar insolation and large area of unused inferior flat land. Countries like Botswana and Namibia have been looking into the possibility of investing such a plant. Carbon credits will also help reduce the overall leveled cost of the plant.

 


 

Bibliography

Pasumarthi, N. and Sherif, S.A. Experimental and theoretical performance of a demostration previous termsolar chimneynext term model¨CPart 1: mathematical model development, J Energy Res 22 (1998), pp. 277¨C288.

Fluri, T.F. et al Cost analysis of solar chimney power plants J. Solar Energy July 2008

Schlaich, J. et al Design of Commercial Solar Updraft Tower Systems¡ª
Utilization of Solar Induced Convective Flows for Power Generation J. Solar Energy Engineering Feb 2005, Vol. 127

Pasumarthi, N. and Sherif, S.A. Experimental and theoretical performance of a demostration previous termsolar chimneynext term model¨CPart 1: mathematical model development, J Energy Res 22 (1998), pp. 277¨C288.

Copyright Yiting Wang 2008