Environmental Engineering Reference
In-Depth Information
Water
Making waves
Water does not travel at the speed of wind. But for the same volume,
it has far greater force because it is more than eight hundred times
denser than wind (which is also why tidal and wave machines have
to be much stronger than wind turbines).
Ocean power
The power of the sea is immense, and endlessly renewable. It comes in
essentially two forms. There is the power of the tides, resulting from the
gravitational pull of the moon and to a lesser extent the sun, and of the
earth's own rotational spin. And there is the power in waves, themselves
created by wind that is a by-product of solar power.
Yet speed has the same disproportionately dramatic effect on water
power as it has on wind. Water energy rises exponentially with water
speed - so that a tidal stream moving at sixteen kilometres an hour will
have
eight
times the force of a current moving at half the speed, at eight
kilometres an hour. Moreover, tidal power may be spasmodic, but it is also
predictably spasmodic (which is unusual for a renewable energy source).
Consult your tidal charts, and you will know months or years ahead when
surges in tidal power will occur.
In contrast to tides, but in common with wind, waves are unpredict-
ably intermittent. But waves are not intermittent on precisely the same
cycle as wind, which should be an advantage in terms of evening out the
flow of electricity from the two sources. Because they are caused by wind,
waves take a certain time to swell up after the wind begins to blow, but
also continue to roll on for a while after the wind stops blowing. There is
also the aesthetic consideration that wave and tidal power machines, lying
on or below the sea surface, are unobtrusive compared to wind turbines.
Inhabitants of the Scottish island of Lewis, for instance, voted against a
