Environmental Engineering Reference
In-Depth Information
shutdowns of all fast breeder prototypes, in the United
States in 1983, in France in 1990, and in Japan in 1995,
and no new viable commercial design is
machines, whose average size rose to 500-750 kW by
the late 1990s and surpassed 1.2 MW by 2003, with 5-
MW machines in development (Øhlenschlaeger 1997;
DWIA 2005).
The second wave of wind projects was pioneered
by Western Europe, above all, by Germany, Denmark,
and Spain, where new laws guaranteed a fixed price for
wind-generated electricity. The Danish government has
been a particularly active promoter. That country now
has the world's highest per capita installed capacity and
dominates the world export market in efficient wind tur-
bines (Vestas 2001). The exponential growth of new
capacities lifted the global total from less than 2 GW in
1990 to 17.3 GW by 2000 and 74.2 GW by 2006, with
Germany accounting for more than one-quarter of the
total (20.6 GW), and the United States and Spain each
having nearly 12 GW (AWEA 2007). With roughly 25%
load factor this implies still no more than about 85
TWh/year, only about 0.5% of all electricity generated
worldwide. The highest national shares were in Denmark
(about 20%), Germany (6%), and Spain (5%); the U.S.
share remained below 1%.
Very large amounts of wind power could eventually
produce some nonnegligible climatic change at continen-
tal scales (Keith et al. 2004), but more practical limits on
global wind capture are imposed by average annual wind
speeds (at least 6.9 m/s are needed for low-cost genera-
tion) and by the height of durable structures. Archer and
Jacobson (2005) put the global wind power potential at
72 TW, but only a very small share of that could be cap-
tured, and even at the best sites wind can be converted to
electricity with only very low power densities. For exam-
ple, Grubb and Meyer (1993) put the practical potential
at 6 TW. Windy sites with annual mean speeds of 7-7.5
m/s produce power densities of 400-500 W/m
2
of ver-
ready for
construction.
The power densities of nuclear fission are high. In nu-
clear engineering the measure denotes the core genera-
tion densities (power per volume). They can go up to
110 kW/dm
3
for PWRs and are highest in fast breeder
reactors (the French Phenix operated with 646 kW/
dm
3
). In terms of power densities as used throughout
this topic (power per unit area), the rates for reactors
are between 50-300 MW/m
2
, 1 OM higher than those
of fossil-fueled boilers. Nuclear power plants do not need
any extensive fuel-receiving and storage facilities, and be-
cause the low-level wastes held temporarily at the site oc-
cupy very small areas, the overall generation densities are
high, typically 2-4 kW/m
2
. Land claims for the com-
plete fuel cycle (mining and processing of ores, uranium
enrichment, production of fuel elements, fuel reprocess-
ing, and storage of radioactive wastes) lower these values
significantly. Gagnon, B´langer, and Uchiyama (2002)
offer an average of about 230 W/m
2
.
Compared to hydro and nuclear generation other
modes of nonfossil electricity production are globally
much less significant. Rapid post-1995 growth elevated
wind-powered generation to third place, but by 2005
its share was still less than 1% of the world's electricity
production. Combined geothermal and photovoltaic
generation do not add up to 0.5%. Modern wind energy
projects began with U.S. tax credits in the early 1980s
(Braun and Smith 1992). By 1985 the United States
had capacity of just over 1 GW, and the world's largest
wind facility was at the Altamont Pass in California. Expi-
ration of the tax credits in 1985 ended this episode. The
early 1990s brought better turbine designs and larger
