44
3 Energy
Figure 3.4 Producer price indices for electricity on the example of Germany (Figure 3.2 is
using the energy price of 2010 as a reference year, taking the 2010 year price value as 100%.)
[St2017, p. 15]
The total energy E of a system is the sum of the inner energy U, the kinetical
energy E kin and the potential energy E pot [AK2014, p. 2].
E = U + E kin + E pot
(3.4)
with E kin =
m ∗ ν 2
2
(3.5)
and E pot = m ∗ g ∗ h
(3.6)
Nonetheless, in practice it is often spoken about energy loss, energy consumption and energy wasting. In a strictly physical sense and according to the second
law of thermodynamics, energy cannot decrease for an isolated system but with
regard to its intended purpose, the usable share is reduced. Especially when transforming thermal energy into electrical energy, the degree of efficiency η is low
and energy conversions are not always completely reversible [He2012, p. 18].
Generally, energy consists of two parts, exergy (E E ) and anergy (E A ) including
the option that one of them can be zero.