Energy conversion and efficiency

Where is energy lost when generating electricity?

Activity Image
20 mins
Group work


After examining a Sankey diagram representing coal-fired electricity generation, students create diagrams of the energy conversions that occur when hydro power is used to generate electricity, and identify where the greatest efficiencies and inefficiencies might be found.


What you'll need

  • "Energy conversion and efficiency" slideshow
  • "Energy conversion and efficiency" worksheet, one for each group
  • Digital projector and screen

  1. Organize your students into small groups (2-4 students) and open up the "Energy conversion and efficiency" slideshow. Show slide 2 and ask groups to suggest where the most energy is lost when coal is used to generate electricity. Encourage groups to use details from the diagram to guide their thinking. 
  2. Invite groups to share their suggestions with the class. 
  3. Display slide 3 and ask groups to compare their ideas with the details from the diagram. Briefly explain that the slide features a Sankey diagram, a visual representation of the energy flow and conversions.
  4. Show slides 4 and 5, ensuring that students understand how to interpret Sankey diagrams.
  5. Provide each group with a copy of the "Energy conversion and efficiency" worksheet. Ask your students to suggest what the arrow suggests about the efficiency of hydroelectric energy. Explain that the challenge of this activity is to create a Sankey diagram for hydroelectric power, drawing the arrows for the conversions that prevent hydro power from being 100% efficient. 
  6. Display slide 6 and encourage groups to use details from the diagram to guide their thinking. Prompt your students to think of the different forms of energy conversions that might take place during the generation of hydroelectric energy.
  7. Conclude the activity by asking groups how the efficiency of a hydroelectricity generating station might be improved: where would they prioritize their efforts to make the greatest improvement in efficiency?

Modify or extend this activity


  • Invite students to create and compare Sankey diagrams for other types of electricity generation. 


  • If your students require more information about hydroelectric energy, consider showing this short video about how a dam works.

Curriculum Fit

Physics 11

Big Idea

  • Energy is found in different forms, is conserved, and has the ability to do work.


  • Conservation of energy; principle of work and energy
  • Power and efficiency

Curricular competencies

Questioning and predicting
  • Demonstrate a sustained intellectual curiosity about a scientific topic or problem of personal, local, or global interest
  • Formulate multiple hypotheses and predict multiple outcomes
Processing and analyzing data and information
  • Seek and analyze patterns, trends, and connections in data, including describing relationships between variables, performing calculations, and identifying inconsistencies
  • Construct, analyze, and interpret graphs, models, and/or diagrams
  • Use knowledge of scientific concepts to draw conclusions that are consistent with evidence
  • Analyze cause-and-effect relationships
  • Evaluate the validity and limitations of a model or analogy in relation to the phenomenon modelled
Applying and innovating 
  • Implement multiple strategies to solve problems in real-life, applied, and conceptual situations
  • Communicate scientific ideas and information, and perhaps a suggested course of action, for a specific purpose and audience, constructing evidence-based arguments and using appropriate scientific language, conventions, and representations


Assess your students’ abilities to:

  • Construct diagrams that accurately reflect scientific principles (e.g., conservation of energy).
  • Appropriately and effectively use scientific language and representations.


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