school energy&environment

Energy efficiency

At this point the notion of efficiency is to be dealt with. As a matter of fact, energy resources are precious goods, which are to be used efficiently and effectively. A basic concept to assess the quality and waste of any human activity is efficiency. Energy efficiency assesses which part of the energy and materials making up any action or process was successful and which part was lost. Energetic transformations too always lead to some losses. The efficiency of an energetic transformation is measured by dividing useful energy (the difference between the energy input and dissipated or wasted energy) by the energy input. If the efficiency of an energetic transformation amounts to 60%, this means that out of 100 energy units included in a process, 60 were transformed into usable energy forms, whereas the other 40 are transformed into non-usable energy forms.
Two meaningful examples can be produced as regards the efficiency of the petrol we use for our cars and the thermal transformations taking place in a thermoelectric power plant. When we travel by car less than one fifth of the chemical energy contained in the petrol is transformed into mechanic energy, i.e. motion. The remaining part is transformed into heat, which cannot be used any more and is dispersed through the radiator or is discharged through the exhaust gas or warms the passenger compartment. Another part of the energy produced is transformed into heat owing to the friction among gears and is dispersed. The total quantity of energy at the beginning and the end of the process does not change, whereas the its form is changed (from chemical energy to motion and heat) and generally degrades into forms which cannot be used to produce work any longer.
In thermoelectric power plants (where fossil fuels are burned to produce electric energy the transformation and use of which by the final users is easier) the average efficiency amounts to 40%. This means the out of 100 energy units contained in coal, oil or natural gas, only 40 are transformed into electric energy, whereas the remaining 60 are transformed into low temperature heat which often cannot be used. In state-of-the-art thermoelectric power plants using natural gas, new technologies allow higher efficiency levels, i.e. approximately 65%.