Environmental Engineering Reference
In-Depth Information
manageable impact on the environment. This topic describes the form this energy
supply must take and how each individual can contribute towards a collective effort
to halt climate change. But fi rst it is important to take a close look at the causes of
today 's problems.
1.1 Energy Supply - Yesterday and Today
1.1.1 From the French Revolution to the Early 20th Century
At the time of the French Revolution in 1789 animal muscle power was the most
important source of energy. Around 14 million horses and 24 million cattle with an
overall output of around 7.5 billion watts were being used as work animals (König,
1999). This corresponds to the power of more than 100 000 mid-range cars.
Power and Energy or the Other Way Around
The terms 'power' and 'energy' are closely linked, and for this reason they
are often confused with one another and used incorrectly.
Energy
is stored work; thus the possibility to perform work. It is identifi ed by the symbol
E
. The symbol for
work
is
W
.
Power
(symbol:
P
) indicates the time during which the work is to be performed or the
energy used.
W
t
work
time
⎛
⎜
⎞
⎟
P
=
power
=
For example, if a person lifts a bucket of water, this is considered work. The work that
is performed increases the potential energy of the bucket of water. If the bucket is lifted
up twice as quickly, less time is used and the power is doubled, even if the work is
the same.
The unit for power is the watt (abbreviation: W). (The fact that the abbreviation for watt
is the same as the symbol for work does not simplify matters.)
The unit for energy is watt second (Ws) or joule (J). Other units are also used for energy.
Appendix A.1 provides the conversion factors between the different units of energy.
As the required powers and energies are often very high, prefi xes such as mega (M),
giga (G), tera (T), peta (P) and exa (E) are frequently used (see Appendix A.1).
The second staple energy source in those days was fi rewood, which was so impor-
tant that it probably changed the political face of Europe. It is believed today that
the transfer of the Continent's centre of power from the Mediterranean to north of
the Alps came about because of the abundance of forests and associated energy
potential there. Although the Islamic world was able to maintain its position of
power on the Iberian peninsula well into the 15th century, one of the reasons why
it lost its infl uence was the lack of wood. The problem was that there was not enough
