Geology Reference
In-Depth Information
direct insolation, is enough to generate around 125 GWh/yr (from a 50 MW plant
at a 10% conversion rate). Thus about 1% of the world's desert areas (240,000
km
2
), if linked to demand centers by high voltage DC cables, could in theory, be
su
cient enough to meet the total global electricity demand forecasted for 2030.
The worldwide 2010 installed capacity was 854 MWe, coming from various power
plants in California and Spain. New projects are rapidly increasing the installed
capacity all over the world, especially in the Middle East and North Africa. Ac-
cording to the CSP Roadmap (IEA, 2010a), there will be a 148 GW global installed
capacity by 2020, with an average capacity factor of 32% (2,800 hours per year).
This equates to an annual production of 414 TWh.
6.6.2 Hydroelectricity
About 23% of the incoming solar radiation (around 40 PW) is the driving force
of the hydrological cycle, which is a conceptual model that describes the storage
and movement of water between the biosphere, atmosphere, lithosphere and the
hydrosphere. About 320,000 km
3
of water evaporates each year from the oceans
and 60,000 km
3
from land (including lakes and streams). Of this total, about
284,000 km
3
fall back into the ocean with the remaining falling on the Earth's
land surface, which becomes eroded on water's eventual journey back into the sea
(Tarbuck and Lutgens, 1984).
The exergy flow used for the evaporation of water is around 38,100 TW (Szargut,
2003). This flow is transformed into the potential exergy of clouds (300 TW) and
only a small part (5 TW) is transformed into that of rivers. Szargut (2003) addi-
tionally calculated the chemical exergy of freshwater reaching the land as rain and
snow at about 6 TW. Hence, the total power derived from water is 11 TW, if the
potential and chemical exergy components are combined (Table 6.8). Valero et al.
(2002b) calculated the exergy replacement costs of renewable water resources and
the world's ice sheets
8
. Their results were between 3,592 and 53,304 Mtoe/yr for
the former and 3:84 10
8
and 7; 210 10
9
Mtoe for the latter.
Society as of yet cannot take full advantage of the chemical and thermal exergy
provided by freshwater and is left to only make use of the potential exergy of rivers
in the form of hydropower, which is in fact the most highly developed renewable
energy resource.
The power present in water that runs off continents was calculated in 1962 as
2.9 TW (Skinner, 1986). The International Water Power & Dam Construction
(IWP&DC) classified and calculated later the world hydroelectric potentials under
the following categories (IWP&DC, 1996):
8
Exergy replacement costs of water resources are defined as the energy required by the best
available technologies to give back seawater its original composition and temperature and return
it to the elevation at which it was originally found (see Chap. 12 for more details).
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