KS4 National and global energy resources
In this final section of the Energy chapter of the AQA Physics specification we will look at where our energy comes from and the main ways we use it.
We will also consider what it means when it is said that one energy resource is "more reliable" than another.
Finally, we will examine some of the environmental implications of using the different sources of energy.
An energy resource or an energy source is, as the words suggest, something from which we can get energy.
A good example is Oil.
Oil is burnt in power stations to produce electricity;
and refined oil (petrol and diesel) is burnt inside engines to move vehicles.
Oil is just one example; there are a lot of other Energy Resources as well as Oil.
Before we describe other Energy Resources we need to distinguish between 2 types of Resource.
Resources are either Renewable or Non-renewable.
A Renewable resource is one that is being, or can be, replenished (replaced) as it is used.
A good example that most people are aware of today is Wind.
Wind is used to turn turbines which are then used to produce electricity, but we say that Wind is a renewable resource because it is always being replaced; it never runs out (or at least not for ever).
A Non-renewable resource is one that is NOT ever replenished (replaced) as it is used.
A good example is the Oil that we mentioned above; it took millions of years to form and so the time to form more is way too large for it to be considered a renewable resource.
We now need to list and write a brief description of each of the main energy resources that are commonly in use.
Note: Since each one is a Store of energy, we have to identify the correct Store for each one that we list.
Before we start - only brief details are going to be given here; you can use text books and the internet to investigate each resource further.
1. Oil: This is a fossil fuel. It is a liquid and it is generally found very deep under the ground including under the sea bed or the ocean floor. Occasionally oil wells can be found closer to the surface.
2. Natural gas: Like Oil, it is a fossil fuel and also like Oil it is found very deep under the ground including under the sea bed or the ocean floor. Obviously it's a gas!
3. Coal: Again, like Oil, it is a fossil fuel, but it is solid and it is often found much closer to the surface of the earth, but more often at depths from 100m to 800m.
Let's pause here to explain "fossil fuels".
They are called "fossil" fuels because they formed from the remains of dead plants and animals.
But these were plants and animals that died millions of years ago and then got covered by earth and rock.
Over the time period of millions of years, under the high pressure and high temperature produced by the covering of earth, the decaying matter broke down into basic carbon structures and became Oil, Natural Gas or Coal.
The 3 Fossil fuels are Chemical Stores of energy.
To release the energy they have to be burned.
In a power station, the heat released is used to turn water into steam which is then used to spin a turbine and generator in order to produce electricity.
Once burned, that particular amount of fossil fuel is gone and is not going to be replaced in a reasonable time scale.
OK, back to our list.
4. Nuclear fuels: these are Uranium and Plutonium.
Nuclear fuels are Nuclear Stores of energy.
In a nuclear reactor the fuel is not burned. Instead it breaks up in a process called nuclear fission which can be controlled and stopped.
When fission occurs, the reactor gets very hot.
As with the fossil fuel power stations, in a nuclear power station, the heat (released around the reactor) is used to turn water into steam which is then used to spin a turbine and generator in order to produce electricity.
Where does the Uranium come from?
Like coal, it is dug from mines, but unlike coal it is found in just a few places in the world. Once used, it is not replaced, which is why we list it amongst the non-renewable sources.
Plutonium, by the way, is derived from Uranium so it too is non-renewable.
The Wind: consisting as it does of moving particles of air, it is a Kinetic Store of energy. The moving air particles strike the blades of a turbine causing it to turn (hence the word "tur-bine"). Its movement is then used to turn a generator in order to produce electricity.
You should be able to think of at least one major problem with using the Wind as a resource for generating electricity. But also, it has significant advantages, doesn't it?
Biofuel: consisting as it does of living or recently living plants or other organisms, it is a Chemical Store of energy. The energy stored in a biofuel can be used for cooking (plant oils), transport (some trucks in the USA run on a biofuel instead of diesel) or generating electricity.
To generate electricity, the procedure is identical to that of a fossil fuel power station; the biofuel is burned, the heat produced turns water into steam, the steam turns a turbine and finally the turbine turns a generator.
Water: there are 3 ways in which Water can be used as an energy resource.
i) Water - Hydro-electric systems.
When used in this way, water is usually held back behind a dam at a high level lake or river, so the water is a Gravitational Potential Store.
The water is released to flow down a pipe. As it flows downwards it moves faster and faster, losing Gravitational Potential energy but gaining Kinetic Energy.
It reaches a turbine (have you noticed how often "turbines" are used with many energy resources?); it makes the turbine turn/spin which then turns a generator to produce electricity.
ii) Water - Tidal systems.
When used in this way, sea water flows through gates in a barrage (like a dam) across a river estuary when the tide "comes in". Due to the tidal flow, the moving water is a Kinetic Energy Store.
As the water flows through the gates, water turbines turn, causing generators to produce electricity.
Once the tidal movement stops, the gates close, holding back the water behind the barrage.
After the tide has gone out and the sea level on the outside of the barrage is lower than on the inside, the gates are re-opened and water flows out, turning the turbines once more and generating electricity for a second time.
So, tidal barrage systems can generate electricity at known times, twice a day.
There is a tidal system being developed in Swansea lagoon at this time!
iii) Water - Wave systems.
When used in this way, it is the up and down wave motion that is used to produce electricity. As with the tidal system, the wave systems view water as a Kinetic Energy Store.
It is not easy to convert the up and down motion of the waves into electricity, but there are a large number of ingenious designs which attempt to do the job, including the Pelamis generator which looks like a giant red snake which floats on the water. As its segments bob up and down with the wave motion, small movements of internal generators occur.
The UK is surrounded by sea, so the potential for using waves to generate electricity is enormous, if the difficulty of the designs can be overcome.
The Sun: since we know that the Sun consists of hydrogen nuclei which are fusing together to produce helium nuclei, at an enormous rate, then we can say that the Sun is a Nuclear Energy Store.
The energy that we receive from it travels or transfers to us via a "Radiation- Energy Pathway" in the form of light waves and other electromagnetic waves.
Natural processes such as photosynthesis make use of the energy from the sun, but now we are making more and more use of this energy also.
For many decades, satellites and space probes have used solar panels to power their on-board electronics and gradually as these panels have got cheaper and cheaper we are seeing them on roof tops around our towns and cities providing electricity for ordinary homes. With no moving parts, solar cells convert the sun's light directly into electricity making a very efficient energy conversion.
Only a few years ago it was thought that solar panels on UK rooftops would be a waste of time since our skies are often overcast with clouds, but modern solar panels do not need direct sunlight. So long as it is daytime, their is sufficient UV (ultra-violet) radiation for the panels to work. Which immediately alerts us to the problem of solar panels! They do not work during the hours of dusk and night.
Geothermal: natural radioactive processes occur deep within the Earth's crust which cause heating of surrounding rocks. When this heat is used to generate eledtricity or simply for heating, we call it geothermal energy. Since its source is nuclear radioactive processes, it is, like the Sun, a Nuclear Energy Store.
Parts of the world where geothermal energy can be used easily are those where there is volcanic activity, where hot geysers and hot springs are found. These can be used to heat cold water, often sufficiently to turn it into steam, to drive a steam turbine and to turn a generator to produce electricity. In places where such high temperatures are not available, the cold water might still be sufficiently heated for it to be used in home central heating systems. In the Philippines, it is estimated that one-quarter of their electricity is generated using geothermal energy. In Iceland, hot water from geothermal sources is pumped under roads in order to keep them free of ice in freezing conditions.
But geothermal energy is not limited to those volcanic regions. The UK has had a number of areas identified as having potential for geothermal projects. Southampton has already developed its own geothermal energy scheme and it heats a number of city centre buildings and generates electricity from a geothermal borehole. Other UK locations could be used if there was government and local support.
Now that we have a full list of the available energy resources, we need to consider how they are used. Put simply, they are used in just 3 ways, for generating electricity, for transport and for heating.
For generating electricity
We have already said a lot about how each of the resources is used to generate electricity, so we are not going to repeat it all here.
What we will do is show how similar are the ways the energy resources are used to generate electricity.
For example, the fossil fuels, nuclear fuel, geothermal and biomass are all used to make Heat, which is used with a Boiler to change water into Steam, which is used to turn a Steam Turbine, which is used to turn a Generator, to produce Electricity.
It is even easier with Wind and Hydro-electric.
With these, you don't need steam, so you don't need the Boiler or Heat.
With all of the above Energy Resources a Generator is needed and the phrase "Generating Electricity" is appropriate.
But with our final resource, the Sun, and using solar panels, a generator is not needed, so a turbine is also not needed.
The solar panel converts the energy from the Sun directly into electricity.
NOTE: You do NOT need to know in any detail how the resources are used to generate electricity.
At the current time in our world, the vast majority of transport vehicles (Cars, Trucks, Motorcycles, Ships (big and small), Aeoroplanes) make use of engines that burn oil based petrol or diesel. So, they use the Energy Resource, Oil. Although more and more train lines are being converted to electric, there are still lots of diesel trains.
So, in the world of transport, Oil is king!
The problem with each vehicle burning the oil is that it puts the source of pollution, the engine of the vehicle, in the heart of the built up areas where people live. If electric vehicles were used instead, then oil might still be burnt at the power station to make the electricity but the pollution would be centralised and measures could be taken to ensure it was as clean as possible, and it would be outside of populated areas.
Another advantage of using electric vehicles is that a huge range of Energy Resources can be put to use in generating the electricity. Oil, on the other hand, will eventually run out.
Did you know that one family sized diesel car is as polluting as 100 similar petrol cars? And that a new small diesel car such as a VW Polo is as polluting as a new diesel truck? (Radio 4, "You and Yours", 6th March 2017)
Whilst electricity can be used for heating, making use of electric wall heaters, the majority of homes in the UK are heated by Gas central heating. Gas is burned and water is heated in a boiler; the hot water is pumped around the house through pipes and radiators.
As noted above, there are a few places where renewable resources such as Geothermal are used for heating but these uses are currently a tiny fraction compared to the use of Gas.
Note: although Gas is the prime resource used in gas central heating, a small amount of electricity is required to power an electric pump to pump the hot water around the house. Which means that when there is an electricity power cut, the gas central heating in your house doesn't work!
What do we mean when we refer to the reliability of an energy resource?
Let's answer by giving an example:
All 3 of the fossil fuels (coal, oil and gas) and nuclear fuel are very reliable resources because we can use them at every time of day, whenever we want or need.
Wind, on the other hand, is a much more unreliable resource because we can never predict when it will be windy.
So, reliablity is really about predictability;
if you can predict when a resource can be used, then it is reliable.
if you can't predict when a resource can be used, then it is not reliable.
Water - Wave as a resource is not reliable because we can't predict when there will or will not be waves.
Water - Tidal as a resource is reliable because although they only occur a few times in a day, we can predict exactly when the tides occur.
Water - HydroElectric is reliable because we decide when to open the valve on the pipe to let the water flow down to the water turbine.
Geothermal is reliable because the "hot rocks" should be hot all the time.
Biomass is reliable because as long as there is a sufficient supply of material, it can be burned at any time, like a fossil fuel.
Fossil fuels: have a significant impact on the environment, producing a lot of waste gases including carbon dioxide which is a "greenhouse" gas which is believed to play a part in global warming. They also produce sulfur dioxide which results in acid rain, damaging building, killing plants and polluting rivers and lakes.
Nuclear fuels: do not produce atmospheric gases, as do fossil fuels, so do not contribute to global warming or to acid rain, but they produce waste products which can be highly radioactive and dangerous for a very long time. Their safe storage is not easy to guarantee and many argue that the waste can't be stored safely. Other possible environmental problems include the possibility that radioactive leaks might occur, though such incidents worlwide are rare.
NB. Be careful not to confuse "radiation leak" with a "radioactive material leak".
Radiation might leak out of a nuclear reactor in the way that light might leak out through cracks in a light shade. And it can be stopped by simply finding the cracks and repairing them.
If radioactive material leaks out from a reactor then that is a whole different problem! Now, we have material that is itself radioactive and dangerous outside the reactor. To make it safe, all of the material has to be traced and cleaned up. This is more like an oil tanker spilling oil into the ocean.
Radioactive materials can be carried by the wind; radiation can't. (Even some textbooks get this wrong!)
Wind: some people say that the wind turbines cause visual pollution and are noisy. There are claims that they injure or kill some birds.
Biofuel: like fossil fuels, biofuels produce the greenhouse gas CO2 when burned, but unlike fossil fuels, the plant that the biofuel comes from uses up CO2 when it is re-grown, so theoretically biofuels should have a neutral effect on the environment. Research is ongoing to confirm whether this is true or not! You should check.
Water - Hydro electric: if a natural lake is used then the environmental impact would be minimal, but usually a lake is enlarged or a new lake is made by flooding a valley, which involves loss of land to people and to wildlife and plants.
Water - Tidal: similar to the hydroelectric system. A tidal barrage is built across a river estuary which would usually involve some flooding at the sides of the estuary, destroying the habitats of wading birds that usually live in such locations.
Water - Wave: it is difficult to assess the environmental impact of wave systems since they can vary so much in design and few have been put into major use. However, as far as the Pelamis type system is concerned, its environmental impact is most likely to be that the number required of the floating "giant snakes" could cause them to interfere with shipping and to trap some fish.
The Sun: the use of solar panels to generate electricity seems to have very limited environmental impact especially when used on rooftops of buildings. The main argument against solar "farms" is when huge areas of land are used for solar panels rather than to use it for agriculture.
Geothermal: when the geothermal systems are "closed loop" which means that the hot water or hot gases are made to flow back down into the ground where they came from, then the environmental impact is small. But if the system is "open loop" and the hot water and gases are allowed to escape, then geothermal systems have the same environmental problems as fossil fuel systems.
Finally, all of the Renewable Resources have one less environmental impact compared to the Non-renewable resources which is that they are not using up a limited natural resource (coal, oil, natural gas or uranium).
Notice, that as scientists we can identify the environmental issues involved in using each of the Resources, as the above brief notes show, but due to political, social or ethical constraints, we can not always deal with the issues.
For example, we might say that since the burning of fossil fuels causes the biggest environmental problems (the production of the greenhouse and acid rain gases) we should stop their use and move to totally renewable schemes.
But to replace all of the fossil fuel power stations overnight with renewable systems would be a task that is far easier to say than to do. The political and economic considerations would be vast.
So, in the real world, we have to balance our knowledge of the environmental implications with those of the political and economic and social worlds.