Environmental Engineering Reference
In-Depth Information
Figure 1.14
Principle of the Global Water Cycle
•
evaporation, precipitation, water flow
•
melting of snow
•
wave movements
•
ocean currents
•
biomass production
•
heating of Earth's surface and the atmosphere
•
wind.
Hydro-electric power
The sun evaporates every year on average 980 litres of
water from every square metre of the Earth's surface, in total 500,000 km
3
(see Figure 1.14). About 22 per cent of the solar radiation energy reaching
Earth is needed to drive this water cycle. Nearly 20 per cent of the evaporated
water rains down on landmasses, where the majority evaporates again. About
40,000 km
3
flows back to the oceans in rivers or groundwater. This is equal to
more than one billion litres per second. Technically, the energy of this flow can
be used.
About 160 EJ is stored in rivers and seas, which is equivalent to roughly 40
per cent of the global energy demand. About one-quarter of that energy could
be technically exploited, so that nearly 10 per cent of the global energy demand
could be provided free of carbon dioxide emissions by hydro-electric power. The
potential for hydro-electric power in Europe is already relatively well exploited,
whereas large unexploited potentials still exist in other regions of the world.
The history of using hydro power reaches back many centuries. Initially,
watermills were used to convert hydro power into mechanical energy.
