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Thermodynamics and engines (A-level only)

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Question 9

AeroGrow Systems is designing a large-scale, automated vertical farming and hydroponic food production complex in a sub-polar region. The average power requirements for the proposed facility are detailed in Table 1 below.

Table 1

RequirementAverage power / MW
For driving water purification, climate-control, and nutrient pumps35
For LED agricultural lighting, ventilation, and automation15
For office administration, security systems, and workspace lighting5
Thermal energy for soil sterilization, space heating, and hot water110

The facility has two potential energy supply strategies:

  • Option 1: Source all electricity from the regional grid (supplied by traditional thermal power stations operating at an average overall efficiency of 40%), and use dedicated natural gas boilers to supply the heating requirements.
  • Option 2: Install an on-site Combined Heat and Power (CHP) system. This consists of a gas turbine with a maximum electrical generation capacity of 60 MW and an electrical efficiency of 35%. The high-temperature exhaust gases from the turbine are routed through a heat recovery system to meet the plant’s thermal demands.

The executive board is evaluating these options.

Write a comprehensive assessment of the two energy supply pathways to advise the board.

In your response, you should:

  • Explain, with reference to the Second Law of Thermodynamics, why the maximum theoretical efficiency of any heat engine is fundamentally limited to well below 100%.
  • Use the numerical data provided to perform a quantitative comparison of the energy inputs, outputs, and any surpluses or deficits under different operating scenarios for both options.
  • Provide qualitative arguments for and against both options to support your final recommendation.
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Thermodynamics and engines (A-level only) Questions

  1. A Level
  2. /Physics
  3. /Thermodynamics and engines (A-level only)

29 exam-style questions on AQA A Level Physics Thermodynamics and engines (A-level only), covering First law of thermodynamics (A-level only), Non-flow processes (A-level only), The $p$ - $V$ diagram (A-level only), Engine cycles (A-level only), Second Law and engines (A-level only), and Reversed heat engines (A-level only). Each one has a worked solution and a mark scheme showing where the marks go.

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