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The National Grid is supplied mainly from power stations which have overall efficiencies of up to about 40% Table 1 shows the average power requirements of a large paper-manufacturing business (a paper mill) - AQA - A-Level Physics - Question 4 - 2018 - Paper 6
Question 4
The National Grid is supplied mainly from power stations which have overall efficiencies of up to about 40% Table 1 shows the average power requirements of a large ... show full transcript
Worked Solution & Example Answer:The National Grid is supplied mainly from power stations which have overall efficiencies of up to about 40% Table 1 shows the average power requirements of a large paper-manufacturing business (a paper mill) - AQA - A-Level Physics - Question 4 - 2018 - Paper 6
Step 1
explain why the maximum theoretical efficiency of a heat engine is much less than 100%
Answer
The maximum theoretical efficiency of a heat engine is dictated by the second law of thermodynamics, which states that not all energy can be transformed into useful work due to irreversibilities in thermal processes.
Heat engines operate between two thermal reservoirs, and the efficiency can be expressed by: ext{Efficiency} = 1 - rac{T_c}{T_h} where is the temperature of the hot reservoir and is the temperature of the cold reservoir. Because of heat losses, friction, and other dissipative processes, practical efficiencies are always lower than 100%. Additionally, real heat engines cannot attain the Carnot efficiency since they operate under less-than-ideal conditions.
Step 2
explain the advantages and disadvantages of the National Grid vs CHP option
Answer
Advantages of National Grid
- No Need to Install Additional Equipment: Energy can be consumed directly without needing a generator.
- High Reliability: A known, established power supply with reduced risk of power cuts.
- Lower Initial Costs: No installation or maintenance costs associated with having a backup generator.
Disadvantages of National Grid
- Higher Costs Over Time: Paying for electricity can be expensive in the long run, especially during peak hours.
- Vulnerability to Power Cuts: The system is susceptible to fluctuations and outages, which could disrupt operations.
Advantages of CHP
- Increased Efficiency: CHP can utilize the heat produced from power generation for other processes, thus enhancing overall system efficiency.
- Cost Savings: Potential grade savings on fuel costs by using waste heat for heating applications.
- Independence from the Grid: Greater autonomy and security in energy supply.
Disadvantages of CHP
- Initial Setup Costs: Higher upfront costs associated with installing a CHP system.
- Maintenance Requirements: Ongoing maintenance will be necessary to ensure efficient operation.
- Less Flexibility: Dependence on specific operational constraints, such as the thermal needs of the paper mill.