Abstract
It is appropriate to underline that the definitions herein introduced differ from those that several authors adopted on the basis of other nomenclatures. For instance, some prefer to define “secondary energies” those types of energy that allow to transfer energy in space or in time, with a view to make it available wherever and whenever needed. In this framework, the name energy vector is ascribed to this type of function.
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- 1.
This concept can be more easily understood by means of an example. Let’s consider the case of electric utilities: since it is known that electric power is stored with difficulty and expensively, it is not easy for Utilities to avail themselves of all the necessary energy. Supplying the electric power demanded by users will entail the ability of providing, moment by moment, the exact quantity of energy requested that is, to say supplying the power demanded second after second.
- 2.
Radioisotopes are the radioactive isotopes of some chemical elements. The word “isotopes” indicates the atoms of chemical species that have the same atomic number, namely that own the same number of protons; for this reason—and this is the etymological explanation—they are positioned at the same level in the scale of elements. However, they have a different number of neutrons in the nucleus, therefore a different atomic weight. Most of elements are available in nature in the form of mixtures of isotopes with constant composition.
- 3.
This is the lower heating value: it is obtained by deducting from the higher heating value the heat deriving from water condensation that is formed during combustion, as well as the latent heat of the humidity contained in the fuel. The higher heating value is the quantity of heat, expressed in kilocalories, generated by 1 kg of fuel by burning entirely, at a constant pressure, when the products of combustion are brought to 0°C and 760 mmHg. Frequently, in case of gaseous fuels, instead of referring to kg, reference is made to the normal cubic meter (Nm3).
- 4.
A barrel of oil corresponds to 158.98 l.
- 5.
A BTU corresponds to the quantity of heat necessary to increase the temperature of a pound of water (1 lb ≅ 4.44 kg) by 1 degree Fahrenheit (1° F ≅ 0.55°C).
- 6.
As a matter of fact, the causes of the variability of solar flow are manifold: the irregularity of the solar surface, the different emissions by the star, the rotation of the Sun and of the Earth around their axis, the variability of the Sun-Earth distance, etc.
- 7.
Renewable sources are those sources with a relatively short recovery period, and in any case comparable to the duration of the utilisation cycle (which guarantees their practically unlimited availability over time). Non-renewable sources, on the contrary, are those sources in which the recovery cycle has a duration largely higher than the utilisation cycle. Usually, non-renewable sources include fossil fuels, since the fossilisation cycle necessary for the formation of fossil fuels has a duration amounting to millions of years (which makes these primary energy sources exhaustible or non-renewable from a practical viewpoint). Even nuclear fuels, deriving from natural raw materials which cannot be regenerated with the present technological processes, have to be considered as non-renewable sources.
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© 2012 Springer-Verlag London Limited
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Orecchini, F., Naso, V. (2012). Energy Systems. In: Energy Systems in the Era of Energy Vectors. Green Energy and Technology. Springer, London. https://doi.org/10.1007/978-0-85729-244-5_1
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DOI: https://doi.org/10.1007/978-0-85729-244-5_1
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