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Author: Iaato Big red star, 1000 posts Old School Fool Add to my Favorite Fools Ignore this person (you won't see their posts anymore) Number: of 37182  
Subject: Re: Uranium from seawater Date: 6/24/2009 7:42 PM
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Those figures at "current best cost" never consider the net cost with rising energy costs.

As usual, a timely quote from a timely blog; the quote is about energy, but applies to materials similarly.

Try to do the same thing with energy, by contrast, and two awkward facts emerge. First, the only reason the iron industry can use progressively lower grades of ore is by using increasingly large amounts of energy per ton of iron produced, and the same rule applies across the board; the lower the concentration of the resource in its natural form, the more energy has to be used to extract it and turn it into useful forms. Second, when you try to apply this principle to energy, you very quickly reach the point at which the energy needed to extract and process the resource is greater than the energy you get out the other end. Once this point arrives, the resource is no longer useful in energy terms; you might as well try to support yourself by buying $1 bills for $2 each.

This difficulty can be generalized: where energy is concerned, concentration counts for much more than quantity. That’s a function of the second law of thermodynamics: energy in a whole system always moves from high concentrations to low. Within the system, you can get energy moving against the flow of entropy, but only at the cost of reducing a larger amount or higher concentration of energy to waste heat. That’s how fossil fuels came into existence in the first place; the vast majority of hundreds of millions of years of energy from sunlight falling on prehistoric plants were degraded to waste heat and radiated into outer space, and in the process a very small fraction of that sunlight was concentrated in the form of carbon compounds and buried underground.

The same rule of concentration explains a great many things that current economic ideas miss. Consider the claims made every few years that we can power the world off some relatively low-grade energy source. Latent heat stored in the waters of the world’s oceans, for example, could theoretically provide enough power for the world’s economy to keep it running for some preposterously long period of time, and any number of inventions have tried to tap that energy. They’ve all failed, because it takes more energy to concentrate that heat to a useful temperature than you get back from the process. The same is true a fortiriori of “zero point energy,” the energy potential that according to current physics exists in the fabric of spacetime itself. It doesn’t matter in the least that there’s an infinite amount of it, or something close to that; it’s at the lowest possible level of concentration, and thus utterly useless as a power source for human society.

The same limits apply, if less strictly, to many of today’s renewable energy sources. Solar energy, for example, is very abundant, but it’s also very diffuse. As with any other energy resource, you can concentrate some of it, but only by letting a larger quantity of it turn into waste heat. It’s quite common to hear the claim that because solar energy’s so abundant, our society can easily power itself by the sun, but this shows a failure to grasp thermodynamic reality. Today’s industrial societies require very highly concentrated energy sources; our transportation networks, our power grids, and most of the other ways we use energy, all work by degrading very high concentrations of energy all at once into waste heat, and without those highly concentrated resources, those things won’t work at all.


http://thearchdruidreport.blogspot.com/2009/06/thermodynamic...
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