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beyond the small area of the support rods. Example
13.3 provides a calculation for the footprint and spac-
ing needed to power the world with 50 percent wind in
2030.
turbines may ultimately be placed over the ocean given
the strong wind speeds there (Figure 13.12).
Considering that 50 percent of wind turbines may be
placed over the ocean, that wave and tidal are already
100 percent over the ocean, that 70 percent of hydroelec-
tric power is already in place, and that rooftop solar does
not require new land, the additional footprint and spac-
ing areas required for WWS power worldwide are only
∼
Example 13.3
Calculate the footprint and spacing area required
for wind turbines from Example 13.2 to power 50
percent of the world's power for all purposes in
2030, assuming a tubular tower plus base circu-
lar diameter of 4 m and a spacing area of
A
t
0.59 percent, respectively, of all land (or
1 percent of all land for footprint plus spacing) world-
wide. This compares with
0.41 and
∼
∼
40 percent of the world's
land currently used for agriculture and pasture.
=
4
D
×
7
D
.
13.6. Material Resources Required
In a global, all-WWS power system, the new technolo-
gies produced in the greatest abundance will be wind
turbines, solar PVs, CSP systems, BEVs, and HFCVs.
This section discusses the availability of materials for
these technologies.
Solution
Under the assumption that each turbine has a
circular base, the footprint area occupied by 3.8
million turbines is 48 km
2
,smaller than the area of
Manhattan (59.5 km
2
). The spacing area required
is 1.69
10
6
km
2
,or1.17percentoftheglobal
land area of1.446
×
×
10
8
km
2
.
13.6.1. Materials for Wind Turbines
The primary materials needed for wind turbines include
steel (for towers, nacelles, and rotors), prestressed con-
crete (for towers), magnetic materials (for gearboxes),
aluminum (for nacelles), copper (for generators), wood
epoxy (for rotor blades), glass fiber-reinforced plastic
(GRP; for rotor blades), and carbon filament-reinforced
plastic (CFRP; for rotor blades). In the future, use
of composites of GRP, CFRP, and steel will likely
increase.
The manufacture of 3.8 million 5-MW or larger wind
turbines to power 50 percent of the world's energy in
2030 (Table 13.4) will require large amounts of bulk
materials such as
steel and concrete
.However, there do
not appear to be significant environmental or economic
constraints on expanded production of these materi-
als. The major components of concrete - gravel, sand,
and limestone - are abundant, and concrete can be
recycled and reused. The world does have somewhat
limited reserves of economically recoverable iron ore
(on the order of 100 to 200 years at current produc-
tion rates, but the steel used to make towers, nacelles,
and rotors for wind turbines should be 100 percent
recyclable).
Copper
is used in coils to conduct electricity in
wind turbine generators. The production of millions
of wind turbines would consume less than 10 percent of
the world's low-cost copper reserves. Other conductors
could also be used instead of copper.
The footprint area required for rooftop solar PV is
zero because rooftops already exist. For nonrooftop
solar PV plus CSP, the spacing areas are assumed to
be the same as the footprint areas. Under this assump-
tion, Table 13.4 indicates that providing 34 percent
of the world's power with nonrooftop solar PV plus
CSP requires about one-fourth of the land area for
footprint plus spacing as does powering 50 percent of
the world with wind, but a much larger footprint area
alone than does wind. However, the footprint area esti-
mate required for solar is conservative because solar
PV power plant panels, for example, can be elevated
above grass with a pedestal, significantly decreasing
the footprint area required for PV.
Geothermal power requires a smaller footprint than
does solar but a larger footprint than does wind per
unit energy generated. The footprint area required for
hydroelectric per unit electric power generated is large
due to the area required to store water in a reservoir.
However, 70 percent of needed hydroelectric power for
a WWS system is already in place.
Together, the entire WWS solution would require the
equivalent of
0.74 percent of the global land surface
area for footprint and 1.18 percent for spacing (or 1.9
percent for footprint plus spacing). Up to 61 percent of
the footprint plus spacing area could be over the ocean if
all wind turbines were placed over the ocean, although
amore likely scenario is that 30 to 60 percent of wind
∼
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