Environmental Engineering Reference
In-Depth Information
can obtain is 36 W/m along the coastline. To generate 1,000 kW, one would need
devices with a length of 30 km. It is presently prohibitively expensive to capture
this energy.
The gravitational pull of the Earth-Moon system produces tides, or the rise and fall
of the ocean level, twice every 24 h. Usually the rise is small (approximately 1 m),
but, occasionally, depending of the geography of the coastal area, there can be lar-
ger rises in bays and estuaries.
The most spectacular of such phenomena takes place in the Fundy Bay in Nova
Scotia, Canada. At the entrance of the bay the tide rise is 5 m, but at the end of the
bay it reaches 13 m.
This movement of the great masses of ocean water can be used to generate hy-
droelectricity. The most important commercial use of tidal energy, presently, takes
place in La Rance, France, where the bay has an area of 22 km
2
and produces ap-
proximately 250 MW of hydroelectricity.
The world's potential for the production of electricity from tides is estimated to
be 3 million MW.
Geothermal energy is the energy that originates from the hot nucleus of the Earth.
As is well known if one drills a well, the temperature increases approximately 2 °C
per every 100 m in depth. Therefore, at a depth of 10 km the temperature is 200 °C
and can be used to produce steam and thus generate electricity. There are, however,
“hot spots” or geysers near volcanic regions where hot water or water vapor is pro-
duced naturally on the surface of the Earth, at high pressure and temperature, mak-
ing it easier to generate electricity. The first geothermal energy plant was installed
in Larderello, Italy, in 1904, and started to produce 250 MW in 1912.
The world's installed capacity for geothermal energy at the end of 2009 was 86
GW electric and 49 GWh thermal. Electricity generated amounted to 47.5 TWh.
The theoretical potential of renewables is enormous; this potential is approximately
5 million EJ/year, or almost 10,000 times more than present consumption of 500
EJ/year. There are, however, problems encountered in converting this potential to
