Life-Cycle Energy & Resource Accounting — Practice · Grade 12 Science

Chapter: Energy, Water & Material Resources

What this practice covers

By the end of Life-Cycle Energy & Resource Accounting you should be able to:

8 questions, numeric and written answer, each with a worked explanation.

Vocabulary used: embodied energy, functional unit, capacity factor.

Problem 1

Delivered energy 300MJ, invested 30MJ. Find modeled EROI.
Hints

Write the relationship first; substitute with consistent units.

Answer and explanation

10

300/30=10.

Problem 2

Why specify a functional unit?
Answer and explanation

It ensures the alternatives provide comparable service.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the calculation or mechanism that supports it.
  • Include units, conditions, or limits where relevant.

Problem 3

A 4 kW unit produces 24 kWh in 12 h. Find capacity factor as a percent.
Hints

List the given quantities, select a relationship, and check units before substituting.

Answer and explanation

50 %

24/(4×12)×100=50.

Problem 4

How does capacity factor differ from efficiency?
Answer and explanation

Capacity factor compares output with rated output over time; efficiency compares useful output energy with input energy.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the calculation or mechanism that supports it.
  • Include units, conditions, or limits where relevant.

Problem 5

Find total A energy over 15 years. Show the reasoning, not just the conclusion.
Hints

A service life shorter than 40 years may prevent break-even.

Answer and explanation

600+20×15=900 MJ.

Problem 6

What could change the estimated break-even result?
Hints

State what the supplied observations or conditions establish, and separate that from any assumption.

Answer and explanation

Different actual use rates, lifetimes, replacements, maintenance, production methods and omitted life-cycle stages.

Problem 7

Break-even compares cumulative accounts over repeated serviceBreak-even compares cumulative accounts over repeated serviceCumulative energy (illustrative units)0100200300400020406080Number of equivalent usesReusable:120+2nDisposable:5n
Calculated hypothetical equal-service energy lines; this is not empirical product LCA data.
Interpret the supplied visual. At60 uses, how much smaller is the reusable energy account?
Answer and explanation

Disposable=300; reusable=240; difference=60 illustrative energy units.

A break-even point is where two cumulative accounts are equal. Here reusable energy is 120+2n while disposable energy is 5n, giving n=40 uses. Before 40 uses the reusable account is larger; after 40 it is smaller under these assumptions. Equality at 40 does not prove every environmental impact also breaks even there. Actual loss, replacement, washing and service differences can shift or remove the threshold.

Disposable=300; reusable=240; difference=60 illustrative energy units.

Response criteria

  • Interpret labels, structures, axes, units and directions correctly.
  • Explain the physical or environmental relationship or mechanism.
  • Respect stated assumptions and distinguish observation from inference.

Problem 8

Reusable production energy is 180 units with 3 units/use; disposable energy is 9 units/use. Find break-even and energy difference after 50 uses.
Answer and explanation

180+3n=9n gives n=30 uses. At50, reusable=330 and disposable=450, a 120-unit advantage in this hypothetical energy category; other impacts need separate accounts.

180+3n=9n gives n=30 uses.

At50, reusable=330 and disposable=450, a 120-unit advantage in this hypothetical energy category; other impacts need separate accounts.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the physical or environmental mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

Browse all courses