2.11 - Hydroelectricity & Tidal Barrages

Hydroelectric power uses falling water

• Hydroelectric power generates electricity from falling water.
• A valley is flooded by building a dam, creating a reservoir that catches rainwater.
• Water is released through turbines: the water's gravitational potential energy at the top is transferred to kinetic energy as it falls.
• The moving water turns the turbines, which drive generators to produce electricity.

Advantages

• No pollution created directly once the dam is built.
• Responds immediately to rising demand - water is released through the turbines whenever extra electricity is needed.
• Reliable in areas with high rainfall; no fuel costs and minimal running costs.

Disadvantages

• High initial cost of building the dam and power station.
• Big environmental impact from flooding the valley - rotting vegetation releases methane and carbon dioxide, and habitats and homes can be lost.
• Reservoirs can look unsightly when water levels drop.
• Unreliable in times of drought, and requires a suitable valley to flood.

Tidal barrages use the Sun and Moon's gravity

• Tides are produced by the gravitational pull of the Sun and the Moon.
• A tidal barrage is a big dam built across a river estuary, with turbines in it.
• As the tide comes in, it fills the estuary. The water is then let out through the turbines at a controlled speed, turning them to drive generators.
• Some barrages also drive the turbines on the way in, generating electricity on both the incoming and outgoing tide.

Advantages

• No pollution once the barrage is running.
• Tides are reliable - they happen twice a day at predictable times.
• No fuel costs and minimal running costs.

Disadvantages

• High initial building costs.
• Prevents free access for boats, spoils the view, and alters wildlife habitats (e.g. for wading birds).
• Lower neap tides provide much less energy than bigger spring tides.
• Doesn't generate electricity when the water level is the same on each side, which happens four times a day.
• Needs a suitable estuary with a large difference between high and low tides.