Sankey Diagrams (Oxford AQA IGCSE Combined Science Double Award)

Sankey Diagrams

• Sankey diagrams can be used to represent energy transfers or energy flow in a system

  • Sankey diagrams are characterised by arrows that split to show the proportions of the energy transfers taking place

• The different parts of the arrow in a Sankey diagram represent the different energy transfers:

  • The left-hand side of the arrow (the flat end) represents the energy transferred into the system

  • The straight arrow pointing to the right represents the energy that ends up in the desired store; this is the useful energy output

  • The arrows that bend away represent the wasted energy

Features of a Sankey diagram

• The width of each arrow is proportional to the amount of energy being transferred

• The law of conversation of energy states that:

Total energy in = total energy out 

Total energy in = Useful energy out + Wasted energy

• A Sankey diagram for a modern efficient light bulb will look very different from that for an old filament light bulb

• A more efficient light bulb has less wasted energy

  • This is shown by the smaller arrow downwards representing the heat energy

Comparing Sankey diagrams for a filament and an energy efficient bulb