Energy Resources and Electricity Generation
Energy resources are classified as renewable (replenished naturally and will not run out, such as solar, wind, hydroelectric, tidal, geothermal and biofuel) or non-renewable (finite and being used up faster than they form, such as coal, oil, natural gas and nuclear fuel). Most large-scale electricity generation uses a fuel or heat source to produce steam, which drives a turbine connected to a generator; the generator converts kinetic energy into electrical energy by electromagnetic induction. Comparing the advantages and disadvantages of different resources (reliability, cost, environmental impact and carbon dioxide emissions), the structure of the National Grid, and calculating the efficiency of a power station using efficiency = useful energy output / total energy input extend the core GCSE course with quantitative National Grid transmission calculations using P = I x V.
Before you start
Make sure you're comfortable with these topics first:
Method
- Classify the resource in the question as renewable or non-renewable, and recall which resources are used directly to spin a turbine (wind, hydroelectric, tidal, wave) and which are used to boil water into steam that then spins a turbine (fossil fuels, biofuel, nuclear, geothermal, concentrated solar).
- For advantages and disadvantages, consider reliability (can it generate on demand, or does it depend on weather), start-up time, running cost, capital cost, carbon dioxide and other emissions, and other environmental impacts (land use, habitat disruption, radioactive waste, visual or noise impact).
- Calculate the efficiency of a power station using efficiency = useful energy output / total energy input, and convert to a percentage by multiplying by 100 if required.
- Explain that the National Grid transmits electrical power at a high potential difference and low current, since a lower current reduces the energy wasted as heat in the transmission cables (power dissipated = current^2 x resistance), and transformers step the potential difference up for transmission and down again for safe use in homes.
- For National Grid calculations, use power = current x potential difference (P = I x V) to compare the current needed to transmit the same power at different potential differences, and explain why the lower current reduces power loss.
- When asked to evaluate or compare two resources, give a specific point for each resource and finish with a justified overall conclusion, rather than just listing facts.
Worked example
A coal-fired power station has a total energy input of 500 MJ per second from burning coal and produces 210 MJ per second of useful electrical energy output. Calculate the efficiency of the power station as a percentage.
- Write down the efficiency equation: efficiency = useful energy output / total energy input.
- Substitute the values: efficiency = 210 / 500.
- Calculate: 210 / 500 = 0.42.
- Convert to a percentage by multiplying by 100: 0.42 x 100 = 42.
- State the final answer with its unit: efficiency = 42%.
Practice questions
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Q1Give two examples of renewable energy resources.Show answer
Answer: Any two of: solar, wind, hydroelectric, tidal, wave, geothermal, biofuel.
Q2State one advantage of wind power over a coal-fired power station.Show answer
Answer: Wind power produces no carbon dioxide (or other pollutants) while generating electricity, unlike burning coal.
Q3State one disadvantage of wind power compared with a coal-fired power station.Show answer
Answer: Wind power is unreliable, since it only generates electricity when the wind is blowing, unlike a coal-fired power station, which can generate on demand.
Q4State the energy transfer that takes place in a generator.Show answer
Answer: Kinetic energy is transferred to electrical energy.
Q5A power station has an efficiency of 35% and a total energy input of 800 MJ. Calculate the useful energy output.Show answer
Answer: 280 MJ (35% of 800 = 0.35 x 800).
Q6State why the National Grid transmits electricity at a high potential difference.Show answer
Answer: A high potential difference means a lower current is needed to transmit the same power, which reduces the energy wasted as heat in the cables.
Q7State the role of a transformer in the National Grid.Show answer
Answer: It steps the potential difference up for efficient transmission, or steps it down again to a safe level for use in homes.
Exam-style questions
Written in the style of a IGCSE Science exam paper, with a full mark scheme.
A power station transmits 400 kW of power along the National Grid. Calculate the current in the cables if the transmission potential difference is (a) 400 V and (b) 400000 V, using P = I x V, and use your answers to explain why a higher transmission potential difference reduces energy losses.
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A country currently generates most of its electricity from a coal-fired power station and is considering replacing it with a combination of wind turbines and a nuclear power station. Evaluate this decision, comparing coal, wind and nuclear power in terms of reliability, carbon dioxide emissions and other environmental impacts, and give an overall judgement.
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Free printable worksheet
Want more practice on paper? Download the energy resources and electricity generation worksheet pack - 6 pages of exam-style questions with a full mark scheme. One email opens every download in this browser for 14 days - no account, no card. Print it for personal and classroom use.
This topic is chapter 28 of IGCSE Science Workbook, the whole course as one free printable PDF.
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