Energy from Water (CIE IGCSE Physics: Co-ordinated Sciences (Double Award))

• Energy can be obtained from the kinetic store of the waves and tides
• The motion of the water is used to turn a turbine, which turns a generator, which generates electricity

Wave power

• Wave power uses underwater turbines 
• The waves move the water which causes the turbines to turn

Turbines using wave power

Underwater turbines generate electricity

Tidal power

• Tidal power uses tidal barrages to store water at a height as the tide comes in and goes out
• When the barrage is opened, water flows through a channel over a turbine

Tidal barrage

A tidal barrage stores water at a height and then opens a gate allowing water to flow over a turbine

Advantages of wave and tidal power

• Wave and tide power produce no pollution or greenhouse gases as no fuel is needed
• No fuel costs
• Tides are regular, so tide power is reliable and predictable
• Large amounts of electricity can be produced at regular intervals
• Wave and tidal power stations are responsive; they can be turned off and on quickly to meet demand
• Wave and tidal power are renewable energy resources
• Smaller power stations are are useful for small islands
• Wave and tidal power stations are inexpensive to build and cheap to run
• Wave and tidal power stations are very efficient (around 80%)

Disadvantages of wave and tidal power

• Tidal barrages are built in estuaries so there are not many suitable locations
• The underwater turbines and tidal barrages can interfere with shipping routes and cause damage to habitats
• The technology for wave and tidal power is not currently advanced enough for large-scale electricity generation
• Wave and tidal power stations have a long construction time compared to some other power station types
• Waves power is unreliable as the waves are not always large enough to turn the turbines

• When water is stored above ground level, it has energy in its gravitational potential store
• This energy can be transferred to kinetic energy if the water is allowed to flow down the slope
• Flowing water turns the turbine to generate electricity

A hydroelectric dam

A hydroelectric dam transfers energy mechanically from the gravitational potential energy store of the water to its kinetic energy store. The moving water turns the turbine

Advantages of hydroelectric power

• Hydroelectric dams are reliable and well established in most countries
• Hydroelectric power stations are responsive because they can be turned on and off easily to meet changing demand
• Hydroelectric power stations are cheap to run
• Hydroelectric power stations can produce large amounts of electricity
• Water is a renewable energy resource

Disadvantages of hydroelectric power

• Valleys are flooded to create the reservoir used to store the water, which destroys habitats, towns and villages
• Pumping systems are sometimes used to return the water to the reservoir
  • Pumping systems use fossil fuels, which release greenhouse gases and pollution into the atmosphere
• Hydroelectric power stations are expensive to build because the land and properties need to be acquired in order to build the reservoir 
• High-voltage power lines are required to transmit electricity to the National Grid
• Drought can affect the supply of water