of the Moon and the Earth results in the oceans bulging out
towards the Moon, whilst on the opposite side the gravitational
effect is partly shielded by the Earth resulting in a slightly
smaller interaction and the oceans on that side bulge out away
from the Moon, due to centrifugal forces. The Earth's rotation
is also a factor in the production of tides.
The technology required to convert
tidal energy into electricity is very similar to the technology used
in traditional hydroelectric power plants except that water is able
to flow in both directions and this must be taken into account in
the development of the generators. The first requirement is a dam
or "barrage" across a tidal bay or estuary. Building dams is an expensive
process. Therefore, the best tidal sites are those where a bay has
a narrow opening, thus reducing the length of dam which is required.
At certain points along the dam, gates and turbines are installed.
When there is an adequate difference in the elevation of the water
on the different sides of the barrage, the gates are opened. This
"hydrostatic head" that is created, causes water to flow through the
turbines, turning an electric generator to produce electricity. Electricity
can be generated by water flowing both into and out of a bay. As there
are two high and two low tides each day, electrical generation from
tidal power plants is characterized by periods of maximum generation
every twelve hours, with no electricity generation at the six hours
mark in between. Alternatively, the turbines can be used as pumps
to pump extra water into the basin behind the barrage during periods
of low electricity demand. This water can then be released when demand
on the system is greatest, thus allowing the tidal plant to function
with some of the characteristics of a "pumped storage" hydroelectric
There are currently two commercial
scale barrages in operation around the world: a 240 MW bulb turbine
at La Rance, Brittany, France and a 16 MW plant at Annapolis Royal,
Nova Scotia, Canada.
The technology required for tidal
power is well developed, and the main barrier to increased use of
the tides is that of construction costs. The future costs of other
sources of electricity, and concern over their environmental impacts,
will ultimately determine whether humankind extensively harnesses
the gravitational power of the moon.
According to the study of Ministry
of Non-Conventional Energy Sources, Government of India, the tides
can be harnessed on commercial basis. Only the Gulf of Kutchh and
Gulf of Cambay in Gujrat and the delta of Ganga on Sunderbans, West
Bengal are so far known as potential sites and feasibility study is
underway. Such study in the state of Maharashtra is yet to be carried
out. Some useful sites as given below may also be referred for details.