View Full Version : Alternative energy from small differences in water temperature

2005-Nov-22, 02:07 AM
This system is described with a few details at www.wired.com/wired/archive/13.06/craven.html The utility of of the electrical generation is somewhat exaggerated, so it is reasonable to suspect the water condenced on cold pipes, air conditioning the hotels etc with cold salt water and the much increased yeild of food crops with cooled roots is also exaggerated. My guess is the system is barely competitive with good luck and few engineering errors in very few locations.
The weak point is bringing the cold 39 degree f water (up three miles and horizontal several miles to the condenser. The condenser can be located at the high tide mark and the turbine perhaps 5 meters higher at some risk that a tsaumi will flood and damage the system. Higher means megawatts to pump the huge volume of water up hill.
Ten kilometers of 2 meter pipe has considerable friction loss if the flow through the pipe is at 100 kilometers per hour. Lower speed means the condencer will occasionally fail to condence, producing a black out or brown out. Worse the column of 40 degree f water has (3%?) more the mass than the column of 60? degree water being pumped downward to turn water turbine powered pumps to pump the 40 degree water upward. Submerable electrical pumps are possible almost 3 miles below the surface, but the extreme pressure and salt water mean poor reliability.
A concentric pipe is likely with the 40 degree f water at the center, 2 meters in diameter, then thermal insulation, then the 60 degree f water decending which will warm the 40 degree water to perhaps 41 degrees by the time it reaches the condenser. The perhaps 3 meter pipe needs thermal insulation for the perhaps 2 kilometers below the surface where the outside water cools to about 65 degrees to avoid heating the 60 degree f water.
The 60 degree f water is pumped downward at very high pressure requiring megawatts of pump power. The very high pressure means the concentric pipe is very costly to assure good reliability immersed in salt water. Actually a third concentric pipe is desirable as the deepest turbine should get the high pressure 60 degree f water first with the pumps closer to the surface getting the turbine discharge consectitively.

The coolant water will exit the condencer at about 43 degrees f and can improve the efficiency of refrigerators, deep freeze, ice makers and water coolers. At about 45 degrees, it can condence potable water from the air and cool hotels etc. At about 55 degrees f it can cool the roots of crops, then go to the high pressure pumps which power tubines far below the surface at 60 degrees f.
For best operation the pressure in the condencer and turbine output should be high vacuum = 2 milibarrs?
The warm water from the surface of the ocean boils at about 75 degrees f at 20? millibarrs, so the turbine has only a tiny pressure and temperature gradient to generate electricity. To produce 200 megawatts it needs to be about 1000 times bigger = ten times taller, ten times wider and ten times longer than a high pressure/high temperature turbine that produces 200 megawatts. Some waste heat above the 85 degrees water temperature can increase the electrical output considerably by super heating the water before it goes to the boiler. On sunny days solar energy can super heat the boiler water and/or the low pressure water vapor that drives the turbine. Please embelish, comment and/or refute as I am mostly guessing how the system works. Neil

Please avoid half truths and false inferences

2005-Nov-22, 02:52 AM
You'll never win by piping cold, denser water up a very long pipe. There's a reason it's way down there, and the potential energy difference is lost when one attempts to bring them together.

Instead, pump a much lighter (ammonia-based) liquid down there to be cooled, returning it to do work in the energy cycle.

The theory is that by using a substance with the approximate same ability to transfer heat/cold, but with less mass, you've beating the reason the water's there in the first place.

Only then will one extract energy from this scheme.

The alternitive line of thought would have us all install energy-generating electronics in the walls of our houses to generate electricity from the difference between the warm inside and cold outside so that we could use that to...

...heat our house.

Uh... Insulation is far more efficient.