7.5 Power to the people8 April 2023

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Aims

• Identify the main stages of power stations. [Level 5]

• Describe the energy transfers involved in electricity generation. [Level 6]

• Describe the factors affecting the development of combined heat and power stations and where they are sited. [Level 7]

Key terms

• Non-renewable energy sources: energy sources that cannot be replaced easily, for example fossil fuels

• Main electricity: electricity that comes into our homes and places of work. The voltage is normally 230 V and the frequency is 50 Hz

Power stations

• Most power station produce electricity by heating water to create steam. This steam is used to turn turbines which rotate a generator to produce electricity

• This electricity is then sent to our homes through the national grid

• The water is often heated by non-renewable energy sources

Fossil fuels

• The efficiency of most power stations is 30% although with newer technologies we can reach 50%.

• When they burn carbon dioxide is produced

Nuclear power

• In a nuclear power station, energy given out during nuclear reactions is used to heat water to steam.

• No burning of fuel occurs so no carbon dioxide is produced

• It does produce radioactive waste which lasts for thousands of years

Producing electricity – ac generators

• Electrical generators use induction to supply electricity. The turbine that is turned by the steam created in the power station boilers rotates a generator which is a large coil of wire between magnets.

• The magnetic field induces a current in the coil

Science focus

• The current produced by an ac generator can be increased by:– Using stronger magnets– Rotating the coil faster– Increasing the number of turns of wire in the

coil– Making the coil thicker

Mains electricity

• The electricity supply in our homes is an alternating current with a frequency of 50 Hz

• This means the current changes direction 50X every second, this is faster than we can see

• Everything is turning on and off 50X a second but we never notice!

Hydroelectric power

• Hydroelectric power stations are one example of the use of renewable energy sources

• Water is stored behind a dam, often high up in the mountains

• The height of the reservoir provides a source of potential energy

• When the water is released and flows downhill, the PE is converted to kinetic energy and the energy turns the turbines

• No burning of fuels so no pollution with nearly 90% efficiency

List the energy transformations that take place in a hydroelectric dam

Wind Power

• Wind turbines use the KE of the wind to turn the turbines to produce electricity

• No pollution is produced but people worry that the wind turbines spoil the view of the countryside and the noise produced

• Although wind is free, the turbines are expensive• No wind, no electricity• When they do operate the efficiency can be

around 35-60%

Solar power

• Solar power can be harnessed using solar cells called photovoltaic cells. When the sun shines on these cells they emit electrons which form a current

• The solar panels are expensive, but the energy source is free and no pollution is produced.

• However, the amount of electricity generated depends on how bright the sunshine is

• As with wind power, the efficiency of energy conversion varies, between 12-25 %

Compare the efficiencies of three renewable methods used to generate electricity and list

their advantages and disadvantages

Getting electricity to our homes and factories

• The UK has a network grid of pylon towers linked by copper cables that transfer electrical energy to our homes

• The voltage produced at the power station is about 25 000 V

• Engineers than increase the voltage to 400 000 V using a step-up transformer

• This reduces the energy losses during transfer, the higher the voltage the lower the current

• A step-down transformer then reduces this to 230 V for your houses (or 11 000 V for some factories)

1. Describe what you would need to do to boil a kettle without electricity.

2. Which of the methods of transferring energyinto electrical energy in lesson 7.5 Power tothe people in the Go Science! 3 pupil bookdo not use fuels?

3. It has been suggested that burning wastecould be used to make steam. State anadvantage and disadvantage of this idea.

4. Describe the energy transfers in ahydroelectric power station. (Hint:remember the water is stored in a reservoirhigh in the mountains before it is releasedto turn the turbine.)

7.5 Power to the peopleQuestions

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(Level 4)

(Level 5)

(Level 6)

(Level 7)

5. It is impossible to create a machine that is100% efficient. Why do you think allmachines will dissipate some energy and inwhat form will this energy be dissipated?

6. Dynamos are connected to the wheels ofbikes and generate electricity by transferringthe kinetic energy of the wheels as electricalenergy to run bicycle lights. Explain twodisadvantages of using dynamos instead ofbatteries to supply electricity for bicyclelights. (Hint: one disadvantage shouldmention energy.)

7.5 Power to the peopleQuestions

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(Level 8)

(Level EP)

7. One solution to the world shortage of oilmight be to build more nuclear powerstations to replace fossil-fuel power stations.Do you think this is a good idea?Explain your answer.

7.5 Power to the peopleQuestions

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(Level EP)