Tuesday, August 3, 2010

On the "quality" of energy

Some interesting concepts were raised in the first chapter of Nelson. Most interesting to me was the relation between total energy, free energy, entropy and the conversion between forms of energy. It refers to a "quality" of an energy and seems to suggest that this quality is related to the entropy and the ease with which this energy is transferred from one form to another.

This raises some questions:

Which forms of energy are "better" than others? Is there a hierarchy of energy?
How to do you measure the entropy of photons?
If heat is the lowest form of energy how can it be so readily used in power stations?

It seems to me that talking in terms of quality is an insufficient concept.


  1. The way I understand a "heat" powered powerplant to work, is that even though the heat energy is of lower quality than the electricity it produces, there is a huge excess of heat energy to the electrical energy produced.

    Furthermore, the heat energy used in a powerplant is usually not initally heat energy, but has recently come from chemical potential energy stored in fossil fuels or the nucleus of a radioactive atom. The heat energy is only useful, because it is in such a high "concentration" due to the recent release of this energy.

  2. I personally wouldn't put energy types in a ranking of best to worse. Each type of energy has its own benefits, and even natural tendency to change into another form. For example, you could rank potential energy high up on your list but when you think about it, potential energy can be just the stored energy of kinetic form, chemical form etc.
    What I conceived about quality was how non-random your energy was, because obviously it is easier to capture and control something that is non-random like sunlight, than it is to catch heat (though of course we have learnt ways to easily create heat).

  3. To understand the power station question, you have to ask: where does the heat come from? You can't just suck heat out of a room to run a power station. The heat comes from somewhere else - burning coal, nuclear decay, falling water, solar energy flux, etc. This energy is turned into heat en route to being something else, but the transfer is inefficient. Nelson is using "quality" to express this inefficiency. I agree that this is a risky gambit.

    Incidentally, has anyone ever read "Zen and the Art of Motorcycle Maintenance"? Its about someone who goes insane trying to define "quality". Very appropriate.