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Broadoak School, Weston-super-Mare

About us & this file

GCSE Physics

Energy Sources
and Power Generation

This file contains only the basic information you need to know for GCSE.
You should aim to find out more than just this!

_____ Contents _____

Clicking on green words will jump you to that topic.
It's best to work through them in the order shown.

Introduction - where did all this energy come from?

How the various methods work

Coal, Oil & Gas

Nuclear power

Hydro-electric power

Tidal power

Wave power

Solar power

Geothermal power

Wind power

Pumped storage reserviors

 Other information

Which ones are renewable?

Which ones are fossil fuels?

(To finish, click on File, then Exit)


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Coal, Oil and Gas
Coal, Oil & Gas

These fuels release energy when they burn. They are all used in the same way in a power station -

Turbines are large fans with many blades.
The steam blows them round like the wind blows a windmill - but much faster and more efficiently.

Once the steam has passed through the turbines it needs to be cooled to turn it back to water so it can go round again. That's what the "cooling towers" at power stations are doing (the bits that look like huge concrete lampshades with steam coming out of the top).

This type of power station provides by far the largest share of the electrical energy used in Britain.


Nuclear
Nuclear Power

A nuclear power station works in much the same way as a "conventional" (coal, oil or gas) station.

The big difference is that instead of burning fossil fuels, they use "nuclear fission" of Uranium -

A nuclear fission reaction occurs when a Uranium nucleus is hit by a neutron, causing it to split into several fragments and release a great deal of energy. (To give you an idea of how much - the energy that a power station gets from a handful of Uranium is the same as a conventional station would get from 100 tonnes of coal.)

Turbines are large fans with many blades.
The steam blows them round like the wind blows a windmill - but much faster and more efficiently.

Once the steam has passed through the turbines it needs to be cooled to turn it back to water so it can go round again. Nuclear power stations don't use "cooling towers", instead they are always built near the sea (or a large river) and they pump in sea water to cool the steam. (So although it's been through a nuclear power station, the sea water doesn't actually go near anything radioactive.)

Nuclear power stations provide around 26% of the electrical power for the UK. Some other countries (such as France & Belgium) get a higher proportion of their energy from nuclear power.

Click here to find out about nuclear fusion


Hydro-electric
Hydro-electric power

Hydro-electric power works by building a dam in an existing river valley to form a reservoir, then allowing water from the reservoir to flow along pipes and turn turbines which drive electrical generators.

This is a simple and reliable way to produce power, but expensive to build. Most of the hydro-electric power stations in the UK are in Scotland.


Tidal
Tidal power

The tide goes in and out twice a day all over the world. This means that if we can find a suitable site, such as a river estuary, we can build a power station to get energy from the flow of water. It looks like a hydro-electric dam (but much larger), and is called a TIDAL BARRAGE.

We allow the water to flow through holes in the barrage and turn turbines just like a hydro-electric dam. But remember that we can only generate power when the tide is flowing, so such a station will not be able to generate continuously like a hydro-electric station.

At present there are no commercial tidal barrages operating in the UK, although there are a number of suitable sites, such as the Mersey and Severn estuaries.


Solar
Solar power

We use two methods to get power from sunlight -
   1) use the sunlight to heat water in a solar panel. (maybe to help a central heating system)
   2) use photovoltaic panels to convert sunlight directly into electricity.
                                                                            (Example - solar powered calculators)

The first method is occasionally used in the UK for domestic installations, but solar power is not used for commercial power generation in this country, because to do so requires strong sunlight.

Many modern buildings are designed so that they make the most of the sunlight that falls on them - this is called passive solar heating.


Geothermal
Geothermal power

This works by pumping water down a borehole to where there are hot rocks, then allowing the heated water to come back up another pipe. Then the hot water can be pumped around buildings to provide central heating.

This situation can also occur naturally - rainwater can find its way into hot rocks. This is called a Geothermal Aquifer. The water may flow back to the surface naturally, or it may need to be pumped up. The city hall in the centre of Southampton is heated this way.

We can't get unlimited heat out of the rocks - if we extract heat too fast we cool the rocks down and have to wait for them to warm up again.


Wind
Wind Power

Windmills have been in use for thousands of years to pump water and to grind grain. More recently, we have also begun to use them to generate electricity.

Modern wind generators have large propellors (usually 3-bladed) and are designed to be very efficient at extracting energy from the wind (unlike old fashioned windmills). The reason that the propellors are large is so that they can extract wind energy from a larger volume of air. The gearbox can usually be automatically adjusted so that both the propellor and the generator turn at their most efficient speeds no matter what the wind speed. The whole thing is mounted on a tower, and is accurately turned to face the wind by a motor, controlled by a wind direction sensor.

"Wind farms" consist of a large number of these generators spread out over a large area.


Renewable sources
Which ones are renewable?

A renewable source of energy is one that ISN'T going to run out because we've used it all up.

So coal, oil & gas are NOT renewable, because once we've got them all out of the ground and burnt them in power stations there won't be any more - one day the Earth will run out of them.

Nuclear power isn't renewable either - once we've dug up all the Uranium and used it in fission reactors, that's it - there won't be any more.
(However it's possible to use special "fast breeder" reactors to get energy from Uranium and turn it into Plutonium at the same time - and then use the Plutonium as a nuclear fuel to get even more energy. But our present nuclear power stations can't do this).

Wind power, solar power, tidal power, wave and geothermal power ARE renewable -  these will keep on supplying energy pretty much for as long as we're here to use it.
Solar power will be useable as long as the Sun keeps shining (so it's got quite a few millions of years yet!), ans so will wind power (because it's heat energy from the Sun that makes winds blow in the first place).

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Fossil fuels

Coal, Oil and Natural Gas are fossil fuels - they're formed from the remains of prehistoric animals or plants. Anything else isn't a fossil fuel.

Click here to go to the "Coal, Oil & Gas" section

Click here to go to the "Which ones are renewable?" section

Remember that crude oil is used to make many things - including tar for roads and petrol for cars.
It's also used to make plastics.

Fossil fuels are the ones that produce large amounts of Carbon Dioxide and other gases when they're burned - the gases that are thought to contribute directly to global warming (the "greenhouse effect").

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Wave power

There is a great deal of energy available from waves on the sea, and several devices have been built to generate electricity from it. Two are shown below :-

At present there are no wave power stations generating commercially in the UK.


Pumped Storage Reservoirs

Strictly speaking, pumped storage reservoir stations are not power stations at all. They don't actually generate power from scratch - they are built in order to STORE energy so that power can be generated very quickly if there's a sudden increase in demand.

The problem is that conventional power stations take quite a few minutes to increase their power output - more fuel has to be burnt and it takes time for the temperature to increase and drive the generators harder. Nuclear power stations take an hour or so to do the same thing, because the reactor temperature can only safely be increased slowly.

But if there's a sudden surge in demand from the national grid (such as everybody putting the kettle on when Coronation Street finishes), we need the extra power within a few seconds - or there'll be power cuts in some areas because the system can't cope.

That's where pumped storage reservoirs come in - during quiet times they slowly pump huge quantities of water up to the top reservoir (see diagram). Then when energy is suddenly needed, the water can be released and quickly flow down to turn the tubines, and large amounts of power can be generated within a few seconds to cope with the demand. This can only be kept up until all the water has run down, which is only a few minutes - but that's long enough for a conventional power station somewhere else to increase it's output and take over the load. Then the pumped storage station can pump the water back up again for when it's next needed.

There is a station of this type at Dinorwic in north Wales. Building it was a huge operation, involving hollowing out a large amount of the inside of a mountain, and installing some serious pumps and generators.


introduction
Where did all this energy come from?

       The Sun is the original source for most of the Earth's energy resources.

Think about it - coal, oil & gas contain chemical energy which we release when we burn them. They were formed from the remains of prehistoric animals or plants. The plants got their energy from the Sun, and animals that ate them got energy from the plants. So the energy we now get from coal, or from petrol to make our cars move, or from gas on our cookers, originally came from the Sun.

Wind power also gets its energy from the Sun. Winds blow because when the Sun warms some air, it rises and other air blows in to replace it. Waves on the sea happen because of wind - so wave power gets its energy from the Sun too. Hydro-electric power relies on the Sun evaporating water from the sea to make it rain into the reservoirs.

However - tidal power and nuclear power DON'T get their energy from the Sun. Tides happen because of the kinetic energy of the Earth and the Moon. Nuclear power relies on energy stored in the elements from which the Earth was formed.

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Nuclear fusion

Nuclear FUSION is a different process, and hopefully one day will be an abundant source of energy. Fusion is how the Sun and other stars shine (LOADS of energy!) but so far we've only managed to make it happen in the lab for a couple of seconds. Research is going on at the Joint European Torus (J.E.T.) project near Oxford.

For a fusion reaction, you need Deuterium and Tritium, which are isotopes of Hydrogen and found naturally in sea water. If these nuclei collide hard enough, you'll get Helium plus a lot of energy. To get them to collide hard enough, you need to heat the mixture to a very high temperature. We are talking 20 million degrees or so - no problem inside a star, but a bit trickier in the lab!

So remember - the Sun's source of energy is a nuclear fusion reaction, in which Hydrogen is converted to Helium.

Fission is splitting big nuclei apart, fusion is sticking small nuclei together. Both release energy.

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about our school
This file was written for KS4 physics in June 1996 by Andy Darvill at :-
          Broadoak School
          Broadoak Road
          Weston-super-Mare                     tel 01926 629106
          North Somerset
          BS23 4NP                                   email seaside@rmplc.co.uk

Files in this series currently are :-
          altenerg.hlp      - this file, written as a single resource to speed up delivery of
                                         the topic, and because pupils tend to like computers.
          emagspec.hlp   - a file similar to this one, about the electromagnetic spectrum.
          scisats.hlp        - a collection of multiple-choice Y9 SATs practice questions.
          scigcse.hlp       - as scisats.hlp, but for GCSE. Contains sections for AT2,3 & 4.

All of these are "freeware" - anyone is welcome to make & distribute copies, as long
as they don't get money for it. Please feel free to contact us for further details.

Disclaimer - the author does not express or imply any warranty of any kind, and
cannot accept responsibility for any problems you may have with or which are
caused by any of these files. It's up to users to ensure that they have properly
licensed software on their machines.


Advantages & Disadvantages of Coal, Oil & Gas power

There are several advantages to these methods. The fuels are not difficult or hazardous to transport, are not very expensive, and not difficult to obtain. A power station can be built almost anywhere so long as you can get large amounts of fuel to it - in the case of coal this means having its own railway link, because many trains must deliver each day. An example of this is at Didcot, between Swindon & Oxford. Oil & gas stations need piped supplies. Gas-fired power stations can be very efficient.

However there are drawbacks, such as the pollution produced by burning the fuels (which is believed to directly contribute to global warming and acid rain). However this can be helped considerably by "flue gas desulphurisation" - using Limestone to neutralise the combustion gases before they reach the chimney (producing Gypsum for the building industry as a by-product). The problem is that this uses a lot of Limestone.
 Huge quantities of fuel are needed continuously, and provision must be made for reserves to cope with fluctuations in both the fuel supply and the demand for power - such as having a sizeable chunk of countryside next door to the power station covered in piles of coal.
These fuels have taken millions of years to form, but we're using them up fast.


Advantages & Disadvantages of Nuclear power

A Uranium fuel rod in a nuclear power station can last for several years. This means that fuel deliveries are only needed infrequently. As for waste, no gases or other forms of pollution are produced, and just one lorry a week is enough to take all the "spent" fuel away for reprocessing.
Nuclear power stations are very safe - they won't explode like an atomic bomb if things go wrong, because they use fuel containing only a small proportion of Uranium-235 (atomic bombs need pure U-235). Reactors in this country are not prone to Chernobyl-style "meltdowns", because they are designed with safety cut-outs that cannot be over-ridden by the operators. (The accident at Chernobyl happened because the engineers over-rode the safety systems so they could try increasing the reactor's power output for a test, without it shutting down automatically in the middle of the test.)

However, if something does go wrong in a big way, it'll have a large impact on a lot of poeple over a wide area - some fallout from Chernobyl landed in the UK.
Although there is not much high-level waste produced by a nuclear power station, it's highly dangerous stuff. The only way that we've found to deal with it is to bury it for hundreds of years until the radioactivity has died away - so it must be put somewhere that we're very sure won't be disturbed by earthquakes or other factors.
Nuclear fuel itself is not dangerous to handle until it's been inside the reactor. But once it's been used, great care must be taken in transporting it from the power station to Sellafield for reprocessing.


Advantages & Disadvantages of Hydroelectric power

There are many hydro-electric power stations in operation, but only about 20% of the world's electricity is generated this way. Although there are many suitable sites around the world, such dams are very expensive to build. However once they're built, the energy is virtually free.

A suitable site needs to be found, in an existing valley (so you only need to build a dam across one end to make a reservoir), and where there will be a sufficient supply of water.
These power stations can generate electricity constantly, and can control their output by controlling the flow of water through the turbines. There is no pollution or other waste produced.

However this method of power generation does involve flooding a large area of land, with implications for farmers and anyone else who lives in or uses that area - as well as affecting the habitats and lifestyles of many plants and animals. So many sites will not be suitable because building the station would have an unacceptable impact on the environment or the residents.


Advantages & Disadvantages of Tidal power

Tidal power is free once you've built the barrage. But building it is very expensive. Tidal barrages can only geneate power when the tide is flowing - just for a few hours each day. But tides are totally predictable, so we can plan when we're going to need more power to be generated by our other types of stations, to make up for those times when a tidal barrage is inactive.

Apart from the huge expense of building it, a tidal barrage has a huge impact on the natural environment over an extremely wide area (tidal schemes make hydroelectric stations look small!). Many species of birds rely on the tide uncovering the mud flats so that they can feed. Countless other animals & plants are also dependant on the coming and going of the tide.

If one was built across the Severn Estuary, the tides at Weston-super-Mare would not go out nearly as far - there'd be water to play in for most of the time. But the Severn Estuary carries sewage and other wastes from many places (e.g. Bristol & Gloucester) out to sea. A tidal barrage would mean that this stuff would hang around Weston-super-Mare an awful lot longer!


Advantages & Disadvantages of Wave power

Once it's built, you get free energy. But waves are extremely variable and unpredictable, so sometimes you'll get lots of power, other times nothing. Suitable sites are needed, such as coastal gullies where the energy of the waves is naturally concentrated.

The design in the left-hand diagram would consist of a long chain of such floats, and to make a reasonable amount of power this would have to be very long indeed - to the point where it could be a problem to shipping.

One big problem is that of building and anchoring something that can withstand the roughtest conditions at sea. An experimental station of the type shown in the right-hand diagram was built off the coast of the island of Islay, in Scotland, in the mid 1990's. However, after a short time it was wrecked by rough weather.


Advantages & Disadvantages of Solar power

Solar power is free, once you've built and installed a means of collecting it. No pollution, no noise, and you don't need to flood valleys or dig up fuel.

To get a useful amount of energy from solar radiation, we need to collect it over a wide area. So that means covering a lot of countryside with solar panels, which aren't cheap. They would not be laid flat on the ground, but would need to be mounted on supports capable of turning to face the Sun as it moves, so the land underneath would still be useable.

Solar power is not really much use in the UK, as we don't get very strong sunlight, and the sun doesn't shine on us often enough!


Advantages & Disadvantages of Geothermal power

Once you've built the power station, geothermal heat is almost free - all it needs is a little energy for a pump (if it needs a pump at all). There are whole towns in places such as Iceland which are heated this way. There is no pollution or any other waste product, and the power station can be quite small, so there is minimal impact on the environment.

This type of power can only be generated in places where there are suitably hot regions of rock, at depths where we can get pipes to them. The hot region of rock must be of a suitable type - preferably full of cracks so that the water we pump down can travel through to the other pipe to get back up.
The nature of the rocks above is also important - drilling through solid Granite to get at the hot region would be too much trouble.
How useful it is depends on how hot the water gets - which depends on how hot the rocks are to start with and how fast we extract the heat.

So the main drawback of this type of power generation is that there aren't that many places where you can do it.


Advantages & Disadvantages of Wind power

Wind power provides free energy and no pollution. "Wind farms" are becoming increasingly common in the UK.

A wind farm needs to be sited where the winds are strong and reliable, most of those in the UK are in Cornwall or Wales. The towers are tall, to get the propellors up off the ground to catch the most wind, so apart from the small base of the tower the land is still useable for farming.

However, people who live near to wind farms often complain of the noise - a constant low "swooshing" throb (day and night!), and many other people feel that covering the landscape with these towers is unsightly.