Environmental Engineering Reference
In-Depth Information
Figure 1.11 Illustration of a 500MW pumped
hydroelectric energy storage facility. The
turbines can be reversed to pump water back
into the reservoir. This formof energy storage in
the electric grid is of larger capacity and lower
cost than any known form of battery. Carters
Dam in Georgia, U.S. (http://en.wikipedia.org/
wiki/File:U.S.ACE_Carters_Dam_powerhoU.S.
e.jpg (http://www.niagarafrontier.com/power.
html).).
1.1.2.3 Ocean Waves
According to Table 1.1, the power available in all the oceans waves is 56 TW, about
3.8 times the global energy consumption at present. Since the area of ocean is
139.4
10
6
mi
2
10
14
m
2
,mi
1609m, the power per unit area from this
estimate is 0.155W/m
2
. This seems small, but of course ocean waves are really a
secondary result of winds, which are themselves a secondary result of the suns
heating.
To check such an arbitrary number, a scientist or technologist should be skeptical
and might seek to test it against his own rough estimate.
¼
3.61
¼
Estimate of Wave Energy
Suppose the average ocean wave amplitude D is 1m and
the average frequency
v¼
2
p
f of the oscillation is 0.1 rad/s. So a wave passes a given
location every 1/f
62.8 s. (These are guesses on the average depth and frequency of
ocean waves). In the simplest model of an ocean wave, the water moves vertically in
simple harmonic motion, y
¼
D
v
cos
v
t, with
maximumspeedD
v
. The energy of this oscillation is, thinking of Mas themass of all
the ocean to a depth 1m,
¼
D sin
v
t. The speed dy/dt is thus
2
E
¼
1
=
2M
ð
D
vÞ
ð
1
:
13
Þ
so that the power dE/dt is
2
P
¼
1
=
2M
ð
D
vÞ
v:
ð
1
:
14
Þ
