Second Law of Thermodynamics

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Description

David Holmgren:

"Second Law: the law of degradation of energy. In all processes some of the energy loses its ability to do work and is degraded in quality. The tendency of potential energy to be used up and degraded is described as entropy, which is a measure of disorder which always increases in real processes."

(First Law: the law of conservation of energy. Energy is neither created or destroyed. The energy entering the system must be accounted for either as being stored there or as flowing out.)

((http://www.permacultureactivist.net/articles/holmgren.htm))


Discussion

David Holmgren:

"The second law of tbermodynamics is based on the concept of energy quality. Examination of tbe natural world from stellar processes through to living systems shows differing forms of energy have varying potential to do work or drive processes. Since all forms of energy can be converted into heat, energy can be defined as:a quantity that flows through all processes, measured by the amount of heat it becomes (the calorie is the unirtof measure of heat energy). Dispersed heat is the most dilute form of energy; it is no longer capable of doing work.

All real processes involve a net degradation in energy quality. However, a proportion of the total energy flow can be upgraded into more concentrated forms of energy capable of driving other processes. This creation of order produces remarkable results, most notably life, but includes such non-living phenomena as rare mineral ores and human-created systerns such as the built environment, culture, and information. However this order is always at a cost of a net degradation of energy. The whole evolution of the Gaia (the living earth) is a small expression of order arising out of the massive energy degradation of the sun's thermonuclear process.

There are thermodynamically fixed relationships between four forms of energy ranging from low- to high-quality. These and similar relationships between energies of differing qualities are fundamental to a correct understanding of the energy basis of nature and human existence. The efficiency of conversion of sunlight to wood (via the processes of photosynthesis) is 8:8000 or 0.1 percent. The apparent inefficiency of this process is due to the very low quality of dilute sunligbt falling on the earth's surface. However 3,800 million years of evolution have optimized this energy harvesting process and any technological "improvement" is highly improbable despite frequent claims to the contrary.

Many kinds of high-quality energy are required for complex work. We tend to think of the energy requirements of a process only as fuel, ignoring human work and contribution of materials. These often involve more energy than the fuels. In running a motor car, the fuel is about 60% of the total energy consumed.

Odum goes on to explain... "The energies involved in the long chain of converging works supporting processes such as educational activities is very large. The total energy required for a product is the embodied energy of that product... The embodied energy of a book is very large compared with the heat energy that would be obtained if the book were burned. For clarity in energy accounting, embodied energy should be expressed as calories of one type of energy such as solar equivalents or coal equivalents."

Many energy studies done by apparently qualified persons and taken seriously by policymakers fail to take account of the simple fact that a calorie of low-quality energy cannot do the same work as a calorie of high quality energy. Consequently completely erroneous conclusions are frequently reached. Such problems have afflicted both high- and low-tech proposals. Nuclear power may be the greatest exarnple of an energy "source" which actually uses and/or degrades more humanly usable energy than it produces. Solar, wind, and biofuel technologies, while appropriate for the use of already embodied energies will never sustain high-energy industrial culture without fossil fuel subsidy.

Computer technologies may similarly be appropriate to make use of manufacturing and network capacity already in place but are in reality very energy expensive due to the very large embodied energy." (http://www.permacultureactivist.net/articles/holmgren.htm)