144
The Last Resource
creates the ‘head’ of water needed to turn the generators. The head
can be built up in two ways in a dammed—oiï estuary or bay: the ride
can be held back by the dam until it builds up high above the level
inside the dam, or the water can enter freely through to the bay until
high tide and then be held back behind the dam wall as the tide
outside recedes before being passed through the turbines. With
either method, water can be pumped to increase the working head—
from behind the dam at low tide in the rst method, or into the
enclosed water at high title in the second. In each case, the energy
.
consumed by the pumps in this technical ‘sleight of hand’ is far less
than that subsequently generated; for example water pumped
behind the dam at high title may be raised nine inches but eventually
this same water will fall many feet, generating power on the way.
Ideally both methods of operation should be used but this would
mean
double of everything, with some turbines and pumps to
handle the incoming title and others for the outgoing water. The
only alternative, using a one—way passage through the generators, is
a complicated system of enclosures arranged in such a way that the
water passes through the generator coming in, and is then cycled
round so that it passes out in the same direction through the gener—
ator. Both systems are clearly expensive and even if the motive
force—the tides—comes free, cost is still important. The break—
through came when French engineers devised machines which
could pump water either in or out and could generate power by
.
allowing water to pass in either direction through them. Thus these
‘bulb sets’, as they are called because of their shape, can replace the
four different machines needed for continuous operation of tidal
power stations. In fact the Rance station has twenty—four bulb sets
let into its dam wall.
Bulb sets allow the power engineers continually to ring the changes
during the tidal cycle. lt does not matter that because of the 50—
minute difference between lunar and solar days the peak generating
power of the tides can occur at off—peak times so far as demand for
electricity is concerned. The choice of pumping, generating and
passive ow can be made to give the best possible results whatever
the state of the tide or the times. The choice is so great that a
computer is needed to make the necessary calculations. Such is the
success of the system, that interested parties have visited it from the
United Kingdom, the United States, Canada, Russia, Germany and
Australia, and several laboratories in the United Kingdom are
The Last Resource
creates the ‘head’ of water needed to turn the generators. The head
can be built up in two ways in a dammed—oiï estuary or bay: the ride
can be held back by the dam until it builds up high above the level
inside the dam, or the water can enter freely through to the bay until
high tide and then be held back behind the dam wall as the tide
outside recedes before being passed through the turbines. With
either method, water can be pumped to increase the working head—
from behind the dam at low tide in the rst method, or into the
enclosed water at high title in the second. In each case, the energy
.
consumed by the pumps in this technical ‘sleight of hand’ is far less
than that subsequently generated; for example water pumped
behind the dam at high title may be raised nine inches but eventually
this same water will fall many feet, generating power on the way.
Ideally both methods of operation should be used but this would
mean
double of everything, with some turbines and pumps to
handle the incoming title and others for the outgoing water. The
only alternative, using a one—way passage through the generators, is
a complicated system of enclosures arranged in such a way that the
water passes through the generator coming in, and is then cycled
round so that it passes out in the same direction through the gener—
ator. Both systems are clearly expensive and even if the motive
force—the tides—comes free, cost is still important. The break—
through came when French engineers devised machines which
could pump water either in or out and could generate power by
.
allowing water to pass in either direction through them. Thus these
‘bulb sets’, as they are called because of their shape, can replace the
four different machines needed for continuous operation of tidal
power stations. In fact the Rance station has twenty—four bulb sets
let into its dam wall.
Bulb sets allow the power engineers continually to ring the changes
during the tidal cycle. lt does not matter that because of the 50—
minute difference between lunar and solar days the peak generating
power of the tides can occur at off—peak times so far as demand for
electricity is concerned. The choice of pumping, generating and
passive ow can be made to give the best possible results whatever
the state of the tide or the times. The choice is so great that a
computer is needed to make the necessary calculations. Such is the
success of the system, that interested parties have visited it from the
United Kingdom, the United States, Canada, Russia, Germany and
Australia, and several laboratories in the United Kingdom are