1.8.3Motion, Forces and Energy
Energy from Water — Cambridge IGCSE Physics 0625 Revision Notes & Topical Questions
5 min read 9 parts Lesson 86 of 91 1 quiz
Lesson summary
1.8.3 Energy from Water — IGCSE PHYSICS notes: Describe how hydroelectric schemes, tidal barrages and wave generators produce electricity and discuss their advantages and disadvantages.Stored water has gravitational potential energy and flowing or moving water has kinetic energy.…
- Energy chain
- Power from falling water
- Pumped storage
- Geothermal
- Water turns a turbine connected to a generator to produce electricity without burning a fuel
- Hydroelectric, tidal and wave resources are renewable
Part 1 of 7Moving water as an energy source
Moving water as an energy source
Stored water has gravitational potential energy and flowing or moving water has kinetic energy.
Water turns a turbine connected to a generator to produce electricity without burning a fuel.
Hydroelectric, tidal and wave resources are renewable.
Part 2 of 7Hydroelectric power
A dam holds back a reservoir at height, and water is released through pipes (penstocks) to a turbine.
Energy chain
- Energy chain gravitational potential energy of the water, kinetic energy of the flowing water, kinetic energy of the turbine, electrical energy.
Advantages:
- Renewable and no emissions in operation.
- Starts up very quickly to meet demand.
- Reservoirs give leisure and water supply.
- Long life and high efficiency, often over 80%.
Disadvantages:
- Flooding a valley destroys habitats and may displace people.
- Very high building cost.
- Needs hilly regions with enough rainfall, and output falls in droughts.
- Dams change river ecology.
Part 3 of 7Pumped storage
Pumped storage
Spare electricity at off-peak times pumps water back to the upper reservoir.
Energy is stored as gravitational potential energy for later use.
It acts as a giant battery.
Part 4 of 7Tidal energy
1
Tides are caused by the gravitational pull of the Moon and Sun.
2
A tidal barrage is a dam across an estuary; water flows through gates and turbines as the tide rises and falls.
3
Advantages:
- Renewable and predictable.
- No fuel and no emissions in use.
- Long-lasting structures.
4
Disadvantages:
- Very expensive to build.
- Changes the estuary and affects fish and wading birds.
- May interfere with shipping.
- Generates only at certain times of the tidal cycle and few sites are suitable.
Part 5 of 7Wave energy
1
Waves are formed by wind blowing over the sea, so they ultimately store solar energy.
2
The up-and-down motion of waves moves parts of a device that drives a generator, or pushes air through a turbine.
3
Advantages:
- Renewable with no fuel and no pollution in operation.
- Useful for islands and coastlines.
4
Disadvantages:
- Output depends on wave conditions.
- Devices can be damaged by storms.
- Costly to build and maintain, and may be an eyesore or boat hazard.
Part 6 of 7Comparing water-based sources
Hydroelectric reservoirs supply on demand, tidal power is predictable but at fixed times and waves vary with the weather.
Power from falling water
- P = mgh ÷ t, using the mass of water falling per second.
Site needs:
- Hydroelectric needs a large height difference and good water supply.
- A tidal barrage needs an estuary with a large tidal range.
- Wave devices need coasts with strong, steady waves.
Each type affects the local environment, so building balances low-carbon electricity against harm to habitats.
Part 7 of 7More from the specification
More from the specification
Hydroelectric and Tidal Power Stations
- Renewable energy systems that harness the gravitational potential and kinetic energy of moving water to generate electricity without burning fossil fuels or emitting carbon dioxide into the Earth's atmosphere.
Environmental Impact Compared to Fossil Fuels
- Unlike coal, oil,
- and natural gas power stations that emit greenhouse gases and sulfur dioxide, water and geothermal energy stations produce no direct atmospheric pollutants.
Nuclear Fission and Nuclear Fusion
- Nuclear power stations currently generate thermal energy through controlled fission of heavy uranium nuclei,
- whereas nuclear fusion joins light hydrogen nuclei under extreme temperatures, powering the Sun.
Solar Photovoltaic Cells and Solar Panels
- Solar cells directly convert light energy into electrical currents,
- while solar thermal panels absorb radiation to warm domestic water systems.
Energy transferred
- W = V Q, in joules.What the symbols mean: E or W = energy transferred (J) · Q = charge (C) · V = potential difference (V) · I = current (A) · t = time (s)
Geothermal
- Energy from hot rocks underground.
Fusion
- Joining of light nuclei into a heavier one.
Biofuel
- Fuel made from recently living plant or animal material.
Fossil fuel
- Fuel formed over millions of years from dead plants and animals.
Solar panel
- A device that uses sunlight to heat water.
Solar cell
- Device that converts light energy directly into electrical energy.
Geothermal energy
- Thermal energy from hot rocks inside the Earth.
Global warming
- Rise in the average temperature of the Earth.
Key terms
| Term | Meaning |
|---|---|
| Hydroelectric | Electricity from water flowing down from a high reservoir. |
| Tidal barrage | Dam across an estuary that generates from tidal flow. |
| Wave generator | Device that uses the motion of waves to drive a generator. |
| Pumped storage | Pumping water uphill to store energy for later. |
| Reservoir | Artificial lake that stores water. |
| Turbine | Machine with blades turned by flowing fluid. |
Avoid these mistakes
1
Saying hydroelectric power has no environmental impact — reservoirs flood land.
2
Confusing tidal and wave energy — tides come from the Moon's gravity, waves come from wind.
3
Saying a tidal barrage gives constant output — it works at certain times of the tidal cycle.
4
Forgetting to name the energy store, such as gravitational potential in a reservoir.
5
Assuming dams can be built anywhere — they need suitable terrain.
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