Energy tower (downdraft)

An energy tower is a method for producing electrical power for consumer consumption, the brainchild of Dr. Phillip Carlson,ref|Carlson which has been expanded upon by Professor Dan Zaslavsky from the Technion.ref|ET-brochure An energy tower produces electricity by drawing the energy from the air around it.

Concept summary

An energy tower is a tall hollow cylinder with a water spray system at the top. The water is pumped up to the top of the tower and then sprayed inside the tower which cools the warm air hovering at the top. The cooled air, being denser than the outside warmer air, falls to the bottom of the cylinder which causes a turbine at the bottom of the cylinder to spin. The turbine is connected to a generator which produces the electricity. The need for large quantities of water may be solved by choosing a location that is not too far from the coast.ref|coast

The tower should optimally be situated in a hot dry climate, which thus allows for the greatest extraction of energy from the air. The hot, dry climate of the horse latitudes is caused by the Hadley cell circulation that is driven by solar heating, which on average is largest near the equator and smallest at the poles. Therefore, the energy that is extracted from the air is ultimately derived from the Sun, so this can be considered a form of solar power. It is a form of solar power that has the peculiar advantage of also working at night. However, power generation by the Energy tower is affected by the weather: it slows down each time the ambient humidity increases (such as during a rainstorm), or the temperature falls.

An alternative approach to this is the solar updraft tower, which would require huge (up to 7 or 8 kilometres in diameter) agricultural glass house collectors to capture the solar heated air. Even though energy towers use some energy (about 50% of the turbine output) by having to pump water to the top and pressurizing nozzles, their advantage is that they require no such large collection areas, because dry air, if available, is continuously drawn at the top from the surroundings.

Implementation

Currently, no known physical implementation of an energy tower exists. However, there are people who say that making a tower to test its capacity can be much easier. This is now being tested in the Netherlands.
Projections made by Altmannref|Altmann and by Czischref|Czischref|Czisch_slides about conversion efficiency and about Cost of Energy (cents/kWh) are based only on model calculationsref|Gutman, no data on a working pilot plant have ever been collected. Actual measurements on the 50kW Manzanares pilot solar updraft tower found a conversion efficiency of 0.53%, although SBP believe that this could be increased to 1.3% in a large and improved 100MW unit.ref|Mills This amounts to about 10% of the theoretical limit for the Carnot cycle. It is not unreasonable to expect a similar low conversion efficiency for the Energy tower, in view of the fact that it is based on a similar principle as the solar updraft tower. It is worrisome that Zaslavsky claims instead that the Energy Tower would achieve up to 70-80% ref|PhysicaPlus of the Carnot limit. If the conversion efficiency turns out to be much lower it is expected to have an adverse impact on projections made for Cost of Energy.

Potential Problems

*If salt water is used, corrosion rates can be very high. Not only would the tower and the turbines be subjected to the salty humid air, but anything nearby or downwind a bit could be affected.ref|Zwirn
*The technology requires a hot and arid climate, and at the same time access to large amounts of water. This poses restrictions to where these plants could be built, such as along the coast of West Africa, Western Australia, northern Chile, Namibia, and along the Red Sea, Persian Gulf, and the Gulf of California. Most of these regions are remote and thinly populated, and would require power to be transported over long distances to where it is needed. Alternatively, such plants could provide captive power for nearby industrial uses such as desalination plants, aluminium production via the Hall-Héroult process, or to generate hydrogen for ammonia production. There is ample precedent for locating large industrial consumers near to cheap sources of electricity. However, given the general lack of infrastructure in many of these desert regions, installations to consume captive power would also require construction from scratch, increasing the capital requirements and overall risk. Nonetheless, given the seemingly limitless demand for energy, combined with oil price increases since 2003 and concerns over global warming, interest in every form of renewable energy seems bound to increase.

ee also

*solar updraft tower
*SHPEGS
*Psychrometrics

References

# US patent reference|number=3,894,393|title=Power generation through controlled convection (aeroelectric power generation)|inventor=Carlson; Phillip R.|y=1975|m=07|d=15
# Zaslavsky, Dan; Rami Guetta et al. (December 2001). PDFlink| [http://www.iset.uni-kassel.de/abt/w3-w/projekte/new_et-brochure_zaslavsky.pdf "Energy Towers" for Producing Electricity and Desalinated Water without a Collector"] |435 KiB . Technion Israel, Israel - India Steering Committee. Retrieved on 2007-03-15.
# cite web | last = Altman | first = Talia | authorlink = | coauthors = Dan Zaslavsky, Rami Guetta and Gregor Czisch | title = Evaluation of the potential of electricity and desalinated water supply by using technology of "Energy Towers" for Australia, America and Africa | work = | publisher = | month = May | year = 2006 | url = http://www.ecmwf.int/about/special_projects/czisch_enrgy-towers-global-potential/report_2006_extended.pdf
format = | doi = | accessdate = 2007-03-18
# cite journal | last = Altmann | first = T. | authorlink = | coauthors = Y. Carmel, R. Guetta, D. Zaslavsky, Y. Doytsher | title = Assessment of an "Energy Tower" potential in Australia using a mathematical model and GIS | journal = Solar Energy | volume = 78 | issue = 6 | pages = 799–808 | publisher = Elsevier Ltd. | month = June | year = 2005 | url = http://envgis.technion.ac.il/publications/energy%20tower%20potential.pdf | doi = 10.1016/j.solener.2004.08.025 | id = | accessdate = 2007-03-12 |format=PDF
# cite web | last = Czisch | first = Gregor | authorlink = | coauthors = | title = Evaluation of the global potential of energy towers | work = | publisher = | month = June | year = 2005 | url = http://www.ecmwf.int/about/special_projects/czisch_enrgy-towers-global-potential/ | format = | doi = | accessdate = 2007-03-13
# cite web | last = Czisch | first = Gregor | authorlink = | coauthors = | title = Aeroelectric Oasis System | work = Global Renewable Energy Potential, Approaches to its Use | publisher = | month = September | year = 2001 | url = http://www.iset.uni-kassel.de/abt/w3-w/folien/magdeb030901/folie_26.html | format = | doi = | accessdate = 2007-03-13
# cite journal | last = Gutman | first = Per-Olof | authorlink = | coauthors = Eran Horesh, Rami Guetta, Michael Borshchevsky | title = Control of the Aero-Electric Power Station - an exciting QFT application for the 21st century | journal = International Journal of Robust and Nonlinear Control | volume = 13 | issue = 7 | pages = 619–636 | publisher = John Wiley & Sons, Ltd. | date = 2003-04-29 | url = | doi = 10.1002/rnc.828 | id = | accessdate =
# cite journal | author=Mills D | title=Advances in solar thermal electricity technology | journal= Solar Energy | volume=76 | issue=1-3 | year=2004 | pages=19–31 | doi=10.1016/S0038-092X(03)00102-6
# cite journal | last = Zaslavsky | first = Dan | authorlink = | coauthors = | title = Energy Towers | journal = PhysicaPlus - Online magazine of the Israel Physical Society | volume = | issue = 7 | pages = | publisher = Israel Physical Society | year = 2006 | url = http://physicaplus.org.il/zope/home/en/1124811264/1137833043_en | doi = | id = | accessdate = 2007-03-13
# Zwirn, Michael J. (January 1997). . Arava Institute for Environmental Studies. Retrieved on 2006-12-22.
# Zaslavsky, Dan (November, 1996). [http://www.consortia.org.il/ConSolar/Sabin/Zas/ZasTOC.html "Solar Energy Without a Collector"] . "The 3rd Sabin Conference".

External links