Renewable energy stores (3) Wave power and tidal barrage power
Wave power for generating electricity
and tidal power electricity generation -
The advantages and disadvantages of these
renewable energy resources
Doc Brown's GCSE level Physics exam study revision notes
The technology of wave power
power: One method of using wave movement is to use its kinetic energy of
up and down oscillation to compress air in a funnel and tunnel the air
through a turbine connected to a generator on the sea shore. It has not so
far (as I know?) proved very successful.
kinetic energy store of the waves ==
mechanically ==> kinetic energy of the turbine and generator rotor ==>
electrical energy as the rotor of the generator rotates in a magnetic field
Note that most of the energy in the
waves originally comes from the kinetic energy store of the wind -
stronger winds make bigger waves.
Advantages of wave power
The initial cost is high, but bar storm
damage, the running costs are low.
Free source of energy and available every
There is no pollution.
A successful scheme might be useful for
an island with a small population.
Disadvantages of wave power
There are several problems eg variable
wave height giving variable power output.
Storm damage is a regular risk.
Spoiling the view.
Hazard to boats.
The seabed may be disturbed affecting the
You need lots of small wave-powered
turbines on the coast to generate a significant power output.
Unreliable due to the variability of wind
speed which affects the wave height and power.
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power - another approach to hydroelectricity generation
The technology of tidal barrage electricity generation plant
Tides are caused by the gravitational
pull of the moon and sun on water, and the flow of tides involves the
movement of huge quantities of
water, and a rise and fall in height of water of several metres.
The Earth spins through the maximum
height of water created by the combined gravitational pull of the Sun
and moon (but don't forget the Earth and moon pull on the Sun too!).
This means the Earth rotates through
two tidal “bulges” every lunar day, producing two high and two low tides
approximately every 24 hours.
Using a tidal barrage is the most
common way to utilise this tidal movement to generate electricity.
A tidal barrage scheme is another
type of hydroelectric power plant that consists of
building a long relatively low dam wall across a river estuary, and
building generators and sluice gate water flow controls into
its internal structure.
Note that the turbine blades can
be designed to operate in both directions so you can extract energy
as the tide comes in and when the tide flows out - but its usual to
generate power when the trapped water is released to flow downstream.
A tidal barrage scheme is the most
common way of utilising the power of the tides in a suitable location
e.g. near the mouth of a river estuary.
The incoming tide is allowed to flow
upstream through the open sluice gates, the collected water is held behind
barrier, so producing a gravitational potential energy store - after you
have closed the sluice gates!
At high tide the sluice gates are
closed, and, at that point, there is no difference in water height
between each side of the barrage dam. The maximum height difference
between the two sides of the dam is governed by the high water mark
(highest tide level) and the low water mark (lowest level of tide).
(You can use the incoming tide to
generate power too - depending on h.)
At the turn of high tide we now
have a great store of gravitational potential energy (GPE) which can be
released to generate power. As the tide recedes, the difference in water
height (h on diagram) increases.
Eventually the difference in height
(maximised at low tide), allows the water to flow back down sufficiently
powerfully to drive the turbines,
Using the sluice gates ('valves') you
can control the conversion of the water's GPE, mechanically into the kinetic energy store
of the water which is
electricity via the turbines and generators in the wall of the barrage.
tide drives the turbines as does the controlled released of the huge amount
of stored water (GPE) stored behind the barrage at high tide.
It is an advantage to store huge quantities of water that can be
released at electricity peak demand times.
Energy store changes:
kinetic energy store of incoming
tide (caused by the gravitational effect of the moon)
==> gravitational potential
energy store (water held behind the barrage)
==> mechanically ==> kinetic energy
store (flowing water)
==> mechanically ==> kinetic energy
store (turbine and generator rotation)
==> mechanically ==> electrical energy
(generator output via rotation of the rotor in a magnetic field)
Advantages of tidal barrage power
The energy from the 'up and down' tidal
movement seawater is free and
there is no pollution and maintenance costs are relatively low.
Its a reliable source of energy
(whatever the weather!) - the
tides rise and fall twice every day due to the combined gravitational
attraction of the Sun and Moon.
Tides are reliable, twice a day, and times/heights can be accurately
predicted, but there periods of time when the water levels are similar on
both sides of the barrage, therefore little effective water flow and no electricity
generation at different times of the day.
A tidal barrage power station can
generate large amounts of electrical energy, unlike many other renewable
Disadvantages of tidal power
Hydroelectric tidal barrage schemes are very costly
to build needing a large capital investment and take a long time to build,
but there are no fuel costs and maintenance costs are relatively low.
There are problems with the water course
become silted up with sand.
Environmental costs - tidal barrages have
a big impact on the local ecology:
Wildlife habitats are affected disrupting
local ecosystems on the estuary bed/seabed and other species from wading birds to fish stocks.
Some might find, as with wind farms,
barrage schemes unsightly.
The height of the tides is variable and
you need a good difference in height to have a large GPE store of water.
There are actually four times in the
day (two high tides and two low tides) when the difference in heights of
the water on either side of the barrage are two small to allow
sufficient flow through the turbines to generate electricity.
The maximum height of tides varies
through the year - lower neap tides and higher spring tides.
Disruption of leisure/commercial craft
on the river and estuary, you need to add locks to allow boats to go up and
down the river from the estuary.
Limited locations where you can build a
hydroelectric tidal barrage scheme - not all estuaries are suitable.
Keywords, phrases and learning objectives
on wave power and tidal power
Be able to describe and explain how a wave power
plant operates to generate electricity.
Be able to describe and explain how a tidal barrage
power plant operates to generate electricity.
Be able to discuss the advantages
disadvantages of generating electricity from wave and tidal
renewable energy resources.
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(1) Wind power and
solar power, advantages & disadvantages
(2) Hydroelectric power and
advantages and disadvantages
Renewable energy - biofuels & alternative fuels,
hydrogen, biogas, biodiesel gcse chemistry
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