Renewable energy (3) Wave power and tidal barrage power

Doc Brown's Physics Revision Notes

Suitable for GCSE/IGCSE Physics/Science courses or their equivalent

wave power for generating electricity

tidal power electricity generation

The technology of wave power

Wave 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.

The initial cost is high, but bar storm damage, the running costs are low.

Free source of energy.

There is no pollution.

A successful scheme might be useful for an island with a small population.

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 ecosystems.

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.

Tidal power - hydroelectricity

The technology of tidal power

Tides are caused by the gravitational pull of the moon and sun, and the flow of tides involving 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!).

A tidal barrage scheme consists of building a long relatively low dam across a river estuary.

Generators are built into the dam wall.

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.

A tidal barrage scheme is the most common way of utilising the power of the tides.

The incoming tide, collected behind a barrier, acts as gravitational potential energy store in a suitable location e.g. a river estuary.

You can use the incoming tide to generate power too.

At the turn of high tide we now have a great store of gravitational potential energy (GPE).

The flow back down is controlled and acts as a kinetic energy store which is then converted into electricity via a generators in the wall of the barrage.

The incoming 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.

gravitational potential energy store (water held behind the barrage)

mechanically ==> kinetic energy store (turbine and generator rotor)

mechanically ==> electrical energy (generator output via rotation of the rotor in a magnetic field)

The energy from seawater is free and there is no pollution and maintenance costs are relatively low.

Its a reliable source of energy - the tides rise and fall twice every day due to the combined gravitational attraction of the Sun and Moon.

Tides are reliable and times/heights can be accurately predicted, but there periods of time when the water levels are similar on both sides, therefore little effective water flow and electricity generation.

A tidal barrage power station can generate large amounts of electrical energy, unlike many other renewable energy schemes.

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.

There are problems with the water course become silted up with sand.

Environmental costs: 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.

Disruption of leisure/commercial craft on the river and estuary.

Limited locations where you can build a hydroelectric tidal barrage scheme.

Energy resources, and transfers, work done and electrical power supply revision notes index

Types of energy store - a comparison with examples explained, mechanical work done and power calculations

Energy resources & uses, general survey & trends, comparing sources of renewables, non-renewables & biofuels

Renewable energy (1) Wind power and solar power, advantages and disadvantages gcse physics revision notes

Comparison of methods of generating electricity, 'National Grid' power supply, mention of small scale supplies

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