Topic 8a:
P1.4.1 Generating electricity
­ conventional energy
Electromagnetic Induction
When a conductor slices through a magnetic field, a voltage is generated in the conductor:
The posh name for this phenomenon is electromagnetic induction
In a power station, high pressure steam spins a spinning turbine.
electromagnet
+ stationary coils
turbine
puny
human
The generator is on the same axle as the turbine.
generator
When the generator's electromagnet spins to make a voltage in the generator's stationary coils.
Fossil fuel power stations
These burn coal or oil or natural gas to release heat.
• the heat turns water into high pressure steam
• the steam spins a turbine
• the turbine spins a generator to make electricity
coal
To the
National
Grid
Coal
Oil
Natural gas
increasing sulfur content
increasing greenhouse gas emissions
Greenhouse gases trap heat in the atmosphere, so adding more greenhouse gas leads to global warming and (almost certainly) to climate change
Sulfur in fuels combines with oxygen to produce sulfur dioxide gas which dissolves in rain clouds to produce acid rain
Advantages:
Conventional (fossil fuel)
Disadvantages:
power plants
• Very large amounts of electricity can be generated in one place using coal, fairly cheaply
• Burning any fossil fuel produces carbon dioxide, which contributes to the "greenhouse effect", warming the Earth
• Transporting oil and gas to the power stations is easy
• It also produces sulphur dioxide, a gas that contributes to acid rain. We can reduce this before releasing the waste gases into the atmosphere
• Gas­fired power stations are very efficient
• A fossil­fuelled power station can be built almost anywhere, so long as you can get large quantities of fuel to it
• Didcot power station, in Oxfordshire, has a dedicated rail link to supply the coal
• Mining coal can be difficult and dangerous. Strip mining destroys large areas of the landscape
• Coal­fired power stations need huge amounts of fuel, which means train­loads of coal almost constantly.
In order to cope with changing demands for power, the station needs reserves. This means covering a large area of countryside next to the power station with piles of coal
Biofuel power stations
These still use steam driven turbines/generators,
but the fuel is obtained from renewable, living sources
Possible fuels are:
• fast growing woods and grasses
• agricultural/household/industrial wastes
• sugar cane pulp (bagasse) is used in Australia and Latin America
BioFuels
Disadvantages:
Advantages:
• all biofuels are carbon neutral.
[CO produced = CO absorbed]
2
2
• biofuels produce less of the other greenhouse gases too
• renewable
• inexpensive to produce
• reduces dependence on imported fossil fuels
• habitat loss as land is used for growing biofuel crops
• farmers may grow more biofuel crops and less food crops. This can lead to inflation and shortages
• research indicates that burning biofuels can produce nitrous oxide ­ another greenhouse gas
Nuclear (fission) power stations
These also use steam driven turbines/generators.
The fuel is uranium or plutonium which produce vast amounts of energy.
Nuclear power
Advantages:
• Nuclear power costs about the same as coal, so it's not expensive to make
• Does not produce smoke or carbon dioxide, so it does not contribute to the greenhouse effect
• Produces huge amounts of energy from small amounts of fuel
• Produces small amounts of waste
• Nuclear power is reliable
The N.I.M.B.Y. effect
(not in my back yard)
Disadvantages:
• Produces nuclear waste which is highly radioactive, highly toxic and remains radioactive for thousands of years
• Parts of the plant become radioactive. The plant is very expensive to decommission
• There are hazards involved in moving nuclear fuel and nuclear wastes around
• No one wants a nuclear waste storage facility near them
• Produces materials that can be used to make nuclear weapons
• Takes a long time to start up/shut down
Meeting the demand ­ Start up times
quickest
}
Natural
gas
Oil
slowest
Coal
These power stations can be started up quickly to meet extra demand, eg, when Eastenders finishes
}
Nuclear
These power plants run all the time to provide the base load of power (the power which is always available on the National Grid)
Power supplied by
the grid (in MW)
Extra demand power is supplied by oil and natural gas power plants which can be started up and shut down quickly
41000MW (the base load)
The base load is the power supplied to the grid at all times
The base load power is provided by coal and nuclear plants that run all the time
Time of day
Excess power sold to France or Ireland via undersea power lines
We don't have the technology to store energy from power stations in batteries ­ use it or lose it!
BUT, we can use surplus energy to pump water up to a storage reservoir
gravitational potential energy
kinetic energy
electrical energy
In times of high demand the water can be released to flow downhill to drive a turbine which drives a generator.
In this way, we "store electricity" in the form of water that has been raised up:
Dinorwig Power Station (1,728MW)
Dinorwig Power Station (1,728MW)
generator
turbine
10 miles of underground tunnels carry water down to the six 288MW turbine generators situated in Europe's largest man­made cavern
During construction 12 million tonnes of material were excavated and 1 million tonnes of concrete and 4,500 tonnes of steel were used