## Physics-SchoolUK.com

### The UK site for KS3 and KS4 Physics

#### KS3 3.3.1 Energy costs

In this section we consider how we pay for the energy we use when it is in its most convenient form - electricity.
We also look at the resources and methods that are used to generate electricity and compare their varied advantages and disadvantages.

### We pay for the energy we use!

Hopefully you will NOT be surprised by the above heading.
Each time you turn on your TV or a room light, you (or your parents) will have to pay for the energy that the device uses.

It is a well known saying that "nothing in life is free" and this is definitely the case when it comes to energy.
Energy costs !

But why does energy cost?

So, why do we have to pay for energy supplied by electricity?

The short answer is - the companies who supply us with the electricity have to spend a lot of money to build the electricity generating plants and to continue to run them.

Let's look at the different ways in which electricity is generated today.

Generating electricity

The 4 most used methods of generating electricity in the UK at the moment are:

• Fossil fuel power station
• Nuclear fuel power station
• Wind power (often called wind farms)
• Solar power

(This is not an exhaustive list; there are others)

The fossil fuels, the nuclear fuel, the wind and the Sun are known as energy resources.

Energy Resources

An energy resource is something with stored energy that can be released in a useful way.

The generating plant takes the energy resource, releases the energy from it and produces electricity.

• Fossil fuels (coal, natural gas or oil) can be burnt releasing heat; this heat can be used to make steam which can turn a steam turbine which can turn an electricity generator.
• Nuclear fuels inside a nuclear reactor, will also release heat; like with the fossil fuels, this is used to make steam, turn a steam turbine and finally a generator.
• The wind can be made to directly turn a wind turbine which will turn an electricity generator.
• The Sun can be made to shine onto solar panels which convert the it's energy directly into electricity.

The first two methods of producing electricity are more similar than you might think

One of the fossil fuels or nuclear fuel is used to make heat which is used to turn water into steam in the boiler.
The steam turns the steam turbine, which turns the electricity generator.

And the third method is like the first two but does without the boiler or the steam.

The fourth resource, the Sun, is the only one which can be used to produce electricity directly; no turbine or generator needed.

The energy resources can be sorted into two important categories, renewable and non-renewable.

Renewable: An energy resource that can be replaced and will not run out. Examples are wind and solar.

a non-renewable resource is the opposite of this:

Non-renewable: An energy resource that can not be be replaced and will run out. Examples are fossil fuels and nuclear fuel.

OK, having learnt a little bit about these 4 energy resources we can finally make a judgement about cost.

The non-renewable energy resources (coal, oil, natural gas and nuclear fuels such as uranium) have to be removed from the Earth by mining or by drilling; these are expensive processes, plus the resources are limited because they are not renewable. All of this makes the energy resources expensive.
However the generating plants themselves occupy small spaces and use relatively tried and tested technology, so they are not too expensive to build.

The renewable energy resources (wind and solar) are free!
However the generating plants occupy very large spaces and use high technology, so they are expensive to build.

So, you should get the idea that it is not straightforward to compare the cost of building and running different types of power plant, but over a very long time period those that use renewable resources should become cheaper because the energy resource is free.

### How we pay for electricity

Regardless of how the electricity is generated, we all pay for electricity in the same way.
It is based simply on the amount of energy that we (or our appliances) use.

The amount of energy that an electrical appliance (such as a TV, a fridge or a computer) uses depends on 2 things:

1. the time the appliance is switched on, and
2. the rate at which the appliance transfers or uses energy (also known as its "power")

Appliances with a high power rating (such as an electric kettle) transfer a lot of energy from the mains electricity supply every second.
Appliances with a low power rating (such as a modern L.E.D bulb) transfer a small amount of energy from the mains supply every second.

So, it will be expensive to have an electric kettle switched on for more than a minute or two.
But it will be not expensive to have a modern L.E.D bulb on for many minutes.

The equation we use to calculate energy transferred is:

Once the amount of "energy transferred", in kWh, is known, the cost is easily found if we know the price of each kWh of electricity.
For example, if the price of electricity is 10p per kWh and the electric cooker in the first example above has transferred 6 kWh, the final cost is 60p.
Alternatively we can use the simple equation:

### Comparing different devices and their Cost

From the above examples and questions you should be able to see that some devices use or transfer a lot of energy because
i) they have a high power rating (a large number of kW), or
ii) they are switched on for a long time, or
iii) both!

Compare: -
a room bulb which could be on for a long time (eg 6 h), but if it is a modern L.E.D type it would have an extremely low power rating (eg 0.01 kW) so it will transfer very little energy ( 0.06 kWh using the numbers suggested).
with:-
an electric shower on for a short time, 10 min (0.166 h), but has an extremely high power rating (eg 8 kW) so it will transfer a lot more energy (1.3 kWh using the numbers suggested).

From the above you can see that you can't easily compare different types of devices because some tend to be used for long periods of time but have a low power rating (eg LED room bulbs) whilst others are used for a lot less time but have a high power rating (eg electric showers, kettles).

What we can do, however, is consider the power rating of an appliance and then consider for how long we should use it.
So, for example, if we want to use a room bulb we recognise its very low power rating so we can use it for many hours and transfer very little energy in that time.
But if we want to boil water using a kettle we should recognise its very high power rating and make sure that we have it switched on for as short a time as possible. To do this we should 1) turn off the kettle as soon as the water starts to boil, and 2) don't boil more water than we need.
For the same reason, if we want to use an electric shower we should recognise its very high power and spend as little time as possible in the shower.

It should be obvious that Cost is directly connected to the energy usage, so if we conserve energy used then we will reduce Cost.

### Comparing energy resources

At the start of this section we listed 4 most used methods of generating electricity in the UK at the moment and these used 4 energy resources:

• fossil fuels
• nuclear fuel
• the wind
• the Sun

Fossil fuels

Fossil fuels are formed from the remains of ancient animals and plants buried deep under the ground or under the oceans. Rigs are often seen out at sea to pump oil or gas from many hundreds of metres below the surface.

Fossil fuels (coal, oil or natural gas) are burned in order to release their stored energy and the resulting heat is used to make steam which is used to turn a steam turbine and finally to turn an electricity generator.

Advantages of fossil fuels as energy resources
• So long as the fuels keep arriving, power stations that use fossil fuels can keep generating electricity 24/7; this makes them a very reliable energy resource.
• The fuels (coal, oil, gas) can be stored and stock piled.
• Fossil fuel power stations are relatively cheap to build and have a very high power output so can provide power to millions of homes.
• Lots of employment opportunities.
Disdvantages of fossil fuels as energy resources
• Fossil fuels are non-renewable which means that once the fuel has been removed from the earth it is not going to be replaced, so the supply is limited; it will run out one day.
• Since it is non-renewable and has to be mined from the earth, each fossil fuel has a cost which can be high and can fluctuate unpredictably.
• When burned, fossil fuels release a waste product, carbon dioxide, which enters the atmosphere and contributes to the greenhouse effect and to global warming.
• When burned, fossil fuels also release sulphur dioxide which contributes to acid rain which damages building, kills plants and pollutes rivers/lakes.

Nuclear fuel

Nuclear fuels release their stored energy inside nuclear reactor and the resulting heat is used to make steam which is used to turn a steam turbine and finally to turn an electricity generator.

Advantages of nuclear fuel as an energy resource
• So long as the fuels keep arriving, power stations that use nuclear fuel can keep generating electricity 24/7; this makes them a very reliable energy resource.
• Nuclear fuel is not burned and no carbon dioxide or sulphur dioxide is released, so does not contribute to global warming or to acid rain.
• The fuel can be stored and stock piled.
• The fuel is incredibly concentrated; 1Kg of nuclear fuel can release the same amount of energy as 20,000 Kg of coal.
• Nuclear fuel power stations have a very high power output so can provide power to millions of homes.
• Lots of employment opportunities.
Disdvantages of nuclear fuel as an energy resource
• Nuclear fuel, like each fossil fuel, is non-renewable.
• Like a fossil fuel it has to be mined from the earth, so it has a cost (however its greater efficiency makes the fuel cheaper).
• Nuclear power stations produce radioactive waste products, some of which remain dangerous for thousands of years and have to be stored very safely at significant expense.
• Decomissioning (taking down) an old nuclear power station can take many, many years since every part has to be safely removed, making it a very expensive process.

The Wind

The wind releases its stored energy when it is used to turn a turbine which is attached to an electricity generator.

Advantages of using the wind as an energy resource
• Wind is, obviously, a renewable energy resouce so will not run out and it is "free", so no fuel cost.
• It does not contribute to global warming or to acid rain.
Disdvantages of using the wind as an energy resource
• The amount of electricity generated changes with the strength of the wind and will be zero if there is little or no wind. This makes the wind an unreliable energy resource.
• Lots of wind turbines are needed to replace one small coal burning power station (about 150).
• Very few employment opportunities once the wind farm is constructed.

The Sun

The Sun releases its stored energy when it shines onto solar panels which convert the it's energy directly into electricity.

Advantages of using the Sun as an energy resource
• The Sun, like the wind, is a renewable energy resouce so will not run out and it is "free", so no fuel cost.
• Also like the wind, it does not contribute to global warming or to acid rain.
• Ideal for individual home use ie they could be placed on the roofs of every home, reducing the need for other types of electricity generating plants.
Disdvantages of using the Sun as an energy resource
• The amount of electricity generated changes as the panels pass from daylight into night and during the day the output will vary to some extent with the amount of cloud cover. This makes the Sun an unreliable energy resource.
• Lots and lots and lots... of solar panels are needed to replace one small coal burning power station (more than a million, taking up at least 1 km X 1 km of land, probably more; but look at the 3rd advantage above for a way around this.).
• Very few employment opportunities once the solar farm is constructed.

#### Keywords

Now that we have reached the end of this section we can focus on the keywords highlighted in the KS3 specification. You have already met each one, but it is important to learn them.

• Power: How quickly energy is transferred by a device (watts).
• Energy resource: Something with stored energy that can be released in a useful way.
• Non-renewable: An energy resource that cannot be replaced and will be used up. Eg fossil fuels.
• Renewable: An energy resource that can be replaced and will not run out. Examples include solar, wind, waves, geothermal and biomass.
• Fossil fuels: Non-renewable energy resources formed from the remains of ancient plants or animals. Examples are coal, crude oil and natural gas.