Comments on: Any working OTEC Ocean Thermal Energy Conversion generators today?

By: WOMBAT, (That Damned....)

WOMBAT, (That Damned....) — Fri, 10 Dec 2010 21:01:07 +0000

OTEC generators are inherently inefficient because of basic thermodynamics.

The maximum efficiency of any heat engine is given by:

eff ≤ 1 – T(sink) / T(source).

(in practice, most engines do not even approach 2/3 this efficiency…)

The surface temperature of seawater, at it’s warmest, is around 36°C, or 527° Kelvin, while near the ocean bottom, it is usually around 3°C (494° Kelvin…)

This means that the maximum efficiency of the best designed OTEC generator would be

eff ≤ 1 – 492 / 527 = 0.0664,

or less than 6.6%. At the absolute best, only around 6% or less of the heat energy that was processed by the generator could be converted into useful work. In practice, it would probably take at least that much energy, simply to *pump* the necessarily large amounts of water or coolant from the seafloor to the surface.

In contrast, coal fired power plants, and “combined cycle” gas turbines, can reach impressive net efficiencies of nearly 40% thermal….

As to the car run by “dead” batteries, you would use way too much energy, simply running around to *collect* the batteries…….

Hope that makes sense,
~W.O.M.B.A.T.

By: Bob M

Bob M — Tue, 07 Dec 2010 11:36:09 +0000

take a look at what the Japanese have been up too. they ave been doing some very interesting work including power generation by virtue of shifting tides… i like the joke

By: mike1942f

mike1942f — Sun, 05 Dec 2010 19:00:32 +0000

I think you misunderstand the product. One of the rules of energy conversion is that it becomes more effective the greater the DIFFERENCE in temperatures or pressures. In this case, the shallower the water, the less the difference. In a river, there is a slight possibility that the very cold water at the bottom of a reservoir might be useful, but as you can see from the referenced site, economics are low.
The car battery video (besides being awful quality) is dumb because it is hardly no cost – there being the transportation of all those heavy batteries and the electricity for charging them. More over, lead batteries by law must be recycled, not dumped, because of the risks of lead in the environment. What he does not say is how many batteries he has to go through to find good ones and how long a charge lasts (not as long as new batteries, I am sure.) “Dead” batteries usually have physical damage inside them.