Energie, Entropie und Umwelt

Aus der Enquete-Kommission “Schutz der Erdatmosphäre”

The author, an engineer, presents an argument in favor of solar energy technologies based on the first two laws of thermodynamics, the law of the conservation of energy, and the entropy law. Mankind's system for tapping energy for such purposes as illuminating rooms, heating water, running appliances, and powering industrial processes and automobiles, can be described in terms of energy conversion chains whose first link is the potential energy contained in some kind of energy source, whose middle link is the steps taken to make this energy available in some desired form and to use it, and whose last link is leftovers, unusables, undesirables like waste heat or pollutants. From a physical viewpoint, the amount of energy at the beginning of the chain has to equal the amount at the end inclusive losses, but its quality is vastly different, each link representing a successive step in its degradation.

Humans cannot do anything about this natural and inevitable tendency toward a final condition of minimum energy value and maximum entropy disorder, but much can be done to slow down the rate. The system for tapping energy which has evolved over the centuries is highly inefficient.

Worldwide, only 10 to 15 per cent of all the energy obtained through sometimes quite laborious technological efforts is the useful portion with an ability to do work, and 85 to 90 per cent is useless.

Our efforts to obtain energy services have led us to produce a gigantic energy downgrading machine for wasting energy by inefficient conversion. Such a situation is only tolerable if sources of energy are practically unlimited and if all the conversion steps are unproblematic. This is not the case.

Our traditional fuels are being depleted at a dramatic rate, and releasing unacceptable levels of pollutants in the process.

Logical remedial measures are to reduce the number of links in energy conversion chains (and therefore lessen the number of steps energy can be degraded) and to increase the efficiency of each conversion step (and therefore lessen the amount of energy degraded).

This can and is being accomplished in many places by increasing the efficiency of the conversion technologies, and by using local energy sources whenever possible, before turning to regional or even global sources, since the latter cost additional energy to store and transport. Something else that can be done is revealed by a comparison of fossil or nuclear energy conversion chains, which begin with an energy raw material like coal, petroleum, natural gas, or uranium ore, with renewable energy conversion chains, which begin with energy forms which are being constantly replenished thanks to the sun, like solar irradiance or wind, waterpower, et cetera.

Although they have the middle part of the chain, conversion technologies, in common, the traditional chains are additionally burdened with costly steps for the processing of energy raw materials, and costly steps to cope with the pollutants generated throughout the chain and originating in these energy raw materials.

In brief: with the fossil and nuclear approaches, the energy required to maintain and cope with the beginning and ending links is not available to perform useful work, not to mention that irreplaceable resources are used up, and pollution increases.

With the solar approach we are supplied with a dependably steady and profligate stream of energy, which we can use to replenish the energy inventory being degraded in our conversion chains.

A similar argument can be made for the second law of thermodynamics applied to matter: If material consumption is to be minimized, solar energy also has an advantage over the traditional chains, since no material is needed for the “lacking” beginn nd end of the solar chains.