*01 Forces&Energy (8-45).qxd
12/11/08
2:10 PM
Page 43
43
Alternative energy sources 2
FORCES AND ENERGY Key words energy generator pressure tidal energy turbine
1 Tidal energy a
b
c
f
a high basin b low basin c upper level
d lower level e turbines f tidal range
1 Tidal energy ● The
first and, to date, the world’s only large-scale tidal barrage was built between 1961 and 1966 across the estuary of the Rance river in France. ● Tides rise and fall and different times of the day. As a tide rises, the level of water in the high basin rises. At high tide all gates are closed trapping the sea water behind the barrage. ● At low tide the water level in the high basin is higher than the water level in the low basin. The water trapped in the high basin has potential energy. It is allowed to flow out through turbine generators which are driven by the moving water to produce electricity.
c
d
d
e
2 Wave energy
i i g
g
2 Wave energy
h
h
j
j g rocking boom h wave
● Rocking
booms are strung offshore where they are kept in continual motion by the waves. As the waves rise and fall the boom is rocked up and down and this motion is used to generate electricity.
i rocking motion j balancing float
3 Tidal swell
k
3 Tidal swell
m
k turbine generator l air chamber m sea movement n air turbine
m
l
n
wave-driven device is built in a natural rock gulley on the coast so that the waves are channelled into it. ● As the wave rolls in, the water level inside the chamber rises and air is forced upwards and out through the turbine generator. ● As the water level falls, the air pressure inside the chamber drops and, due to atmospheric pressure, air is forced in through the turbine generator. ● The turbine is a special design called a Wells turbine which can extract energy from the air stream no matter in which direction it flows so electricity is generated both as the water level rises and falls.
© Diagram Visual Information Ltd.
● The
l