Tidal Energy
ORIGIN
Tidal Energy has been used for centuries in small mini type situations where the natural conditions make it
possible. Further research into this energy source has come about due to the public awakening to the impact
of fossil fuels and their call for further development into cleaner, more environmentally friendly sources of
energy production. Conservation is put forth as a preferred method of reducing greenhouse emissions, but
few experts see conservation as a realistic solution.
The two countries leading the way in the development of tidal energy, infact the only two
countries of three which have operating tidal power generation systems; are Canada with a 16MW plant at
Annapolis Royal, Nova Scotia, and France with a 240 MW bulb turbine at La Rance, Brittany.
TECHNOLOGY
A tidal generator can be capable of inexpensive commercial scale electrical power production that utilizes
the ocean tides as its sole power source. The generation of electricity from the tides is very similar to
hydroelectric generation, except that water is able to flow in both directions. The simplest generation
system for tidal plants is the ebb generation system.
Ebb Generation System
The simplest generation system for tidal plants, known as an ebb generation system, involves a dam, known
as a barrage across an estuary. Sluice gates on the barrage allow the tidal basin to fill on the incoming high
tides and to exit through the turbine system on the outgoing tide (known as the ebb tide). As the water
passes through the turbine system, it turns the turbine and the usual technique of electricity generation
occurs. This is the generation system used at La Rance, France, with a bulb turbine (there are a number of
different turbines that can be used in tidal plants).
LOCATION
A tidal power station can be built anywhere where there is a large enough river estuary; for example a
power station built across the Severn Estuary is being considered.
The Annapolis Tidal Generation System, Nova Scotia, Canada
The Annapolis Tidal Generating Station was completed in 1984. It was a pilot project sponsored by the
provincial and federal governments designed to explore the potential of harnessing energy from the sea.
Annapolis Tidal utilizes the sea water of the Bay of Fundy. Tides, which can sometimes reach 21 feet in
height, rise and fall every 12 hours and 25 minutes in harmony with the gravitational forces of the Sun, the
Earth, and the Moon.
This facility has the distinction of being the first and only modern tidal plant in North America. The station
is located in Annapolis Royal by the Bay of Fundy, home of the world's highest tides. Twice a day, the tide
comes in and out. Twice a day the turbine turns. Twice a day electricity is generated which is supplied to
the provincial electric grid.
Annapolis uses the largest straflo turbine in the world to produce more than 30 million-kilowatt hours per
year - enough to power 4,000 homes.
Annapolis is one of three tidal power plants in the world. The largest plant is located in France, in the
estuary of La Rance near St. Malo. With a capacity of 240 megawatts, it generates on the incoming and
outgoing tide. The output capacity of Annapolis Tidal is 20 megawatts. The smallest tidal plant is located at
Kislaya Guba on the White Sea in Russia. It has a 0.5 megawatt capacity.
ADVANTAGES / DISADVANTAGES
Tidal power can provide advantages such as improved transportation due to the development of traffic or
rail bridges across estuaries and reduced greenhouse emissions by utilizing tidal power in the place of fossil
fuels. It would also not require waste disposal, or release 17 million tonnes per yr in acidic emissions
(Greenhouse effect). Work on environmental and regional issues has identified possible benefits that would
occur with a barrage in operation. These include the protection of a large stretch of coastline against storm
surge tides ie. Thames barrier, opportunities for water based recreation, increased land and property values
and a substantial creation of employment.
There are also ecological and tidal changes that could take place. A lowering or raising level in the tidal
basin could have an effect on the sedimentation and turbidity of the water within the basin. Navigation and
recreation can be affected as a result of sea depth change due to increased sedimentation in the basin. A
raise in tidal level could result in flooding which could have an effect on the marine food chain.
As few tidal barrages have been built little is understood of the impacts on the local environment. It has
been seen that the habitat of seabirds and fish migration routes has been effected.