Power Tower Proposal

Letters to the Editor, New Scientist

Power Tower Extras
(New Scientist, July 31, 2004)

The planned Power Tower in the Australian outback(www.enviromission.com.au/intro.htm) can produce more than electrical power. It can also be used to provide much needed fresh water. In the outback area the ground water is plentiful but is too salty for drinking or for irrigation. This salt water can be evaporated in troughs under the solar collection surface. In this area the air will be very hot and able to evaporate all of the water leaving behind only solid salts. The value of the salts can be increased by using long troughs arranged like the spokes of a wheel for evaporation. This will result in individual salts crystallizing out in different areas of the troughs depending on their solubility. The salts can be collected separately and sold for high prices because they will have high purity. A large amount of water can be treated since hot air can hold much more moisture than cold air. As the hot humid air rises up the stack, it cools by expansion and some of the water condenses out and is captured inside the stack using drip nets.
The addition of the desalination component to the project will require a larger solar collector area but will also increase the amount of energy that can be produced. This is because the moist air rising in the stack will not cool as fast as dry air would since the water condensing out will release heat. This is the energy that drives hurricanes and should substantially increase the output of the turbines.
As the air leaves the stack at the top it will still have considerable moisture in it. This moisture will fall as rain downwind of the stack as the plume of hot moist air continues to rise. Thus a large area around the stack will become productive farmland. Some of the fresh water collected in the stack can be used for growing vegetables under the periphery of the solar collectors. This water will be recycled back into the system.
Two additional benefits of this addition are that the water filled troughs will provide heat storage and, in the long term, the salinity of the aquifer will be reduced since salt is constantly being removed.
William Isecke
541 Queen Anne Road
Teaneck, NJ 07666, US
201 836 8403