What is a Sankey Diagram

Sankey Diagram - Definition

Sankey diagrams - definition:

At a Sankey diagram it is a special type of flowchart in which the flow rates are indicated by arrows proportional to the amount: the width of the arrow represents the amount to scale.

In addition, in a Sankey diagram, directed flows always run between two nodes (processes), and consequently, in addition to the quantities, they also transport other information, such as the division or structure of systems.

Sankey diagrams are therefore an effective alternative to conventional flow diagrams or bar and pie charts, especially when it comes to depicting energy flows and volume flows in production plants.

They are used, among other things, in energy management, facility management (building technology), in process technology or in system technology.

Why should I use Sankey diagrams?

When it comes to depicting rivers, Sankey diagrams offer a number of advantages over conventional diagram types:

  • They show rivers with arrows proportional to the amount: the wider the arrow, the greater the amount of flow. As a result, they immediately direct the viewer's gaze to the essential mass flows.
  • They have directional arrows: Sankey diagrams show flows that flow from one node (source, warehouse, process, machine) to another node. This makes them ideal for mapping flows in production systems or along the value chain.
  • With a Sankey diagram communicate your message in an appealing way: both within the project team and externally to customers or partners.

Sankey diagrams are named after the Irish engineer Captain Matthew H.R. Sankey (1853-1925)

History of the Sankey Diagrams

The first representation of energy flows with arrows proportional to the amount was created by the Irish engineer Captain Matthew Henry Phineas Riall Sankey in 1898. He used it to compare the energy efficiency of different steam engines. This diagram form was previously chosen by the French civil engineer Charles Joseph Minard for the representation of the troop losses of the French army during Napoleon's Russian campaign.

Captain Sankey only drew one Sankey diagram and so this form of representation was quickly forgotten again until the Austrian mechanical engineer Alois Riedler (1850-1936) used Sankey diagrams to examine the performance and energy losses of cars at that time.

In the course of this, Sankey diagrams became increasingly popular, especially in Germany, among other things because, due to the reparation payments after the First World War, the German economy focused on material and energy efficiency.

After a renewed decline in use, Sankey diagrams have recently gained popularity again and are now used across the board, e.g. for material flow analyzes or in energy management.

Example diagrams:

Below are some examples of different Sankey diagrams. All diagrams were created with our software e! Sankey.

Example 1: Energy use in the car

This Sankey diagram shows the proportions of energy used in a car. In addition to the energy actually used (mechanical energy on the wheel, drive), a large part of the energy is lost as losses (especially heat losses). Other consumers in the vehicle are also shown.

The numerical values ​​are displayed both in percentages and in absolute numbers (based on a petrol consumption of 6.57 liters / 100 km). The rivers on the arrows are differentiated by color and - as is usual with Sankey diagrams - their widths are exactly proportional to the flow rates.

(Source: Prof. Mario Schmidt, INEC, Pforzheim University)

Example 2: Food losses

In this diagram, the quantitative losses along the food process chain are visualized. It shows the percentage losses in each level as an arrow that branches off downwards. One recognizes an "efficiency" in the production and use of food.

So here no absolute quantities are given, only proportions are shown.

Source: David Lisle, Know The Flow Blog, based on data from a FAO study.

Example 3: Battery in an electric vehicle

Often, but not always, Sankey diagrams are oriented from left to right (along the reading direction of many scriptures). Especially when feedbacks (loops) are to be displayed.

In this example, the arrows run from top to bottom and from bottom to top or counterclockwise: It shows the battery cycle in an electric car, with losses branching off.

Source: sankey-diagrams.com

Example 4: energy balance

Sankey diagrams are also often used to visualize the energy balance of a region or country. Instead of confusing tables with statistical data, the shares of the various energy sources, imports and exports, and finally the use of energy in different sectors are shown here.

In this specific example it concerns the energy balance of Malaysia for the year 2011. The rivers are in the unit 'Mtoe'.

Source: Chong, C .; Ni, W .; Times.; Liu, P .; Li, Z. The Use of Energy in Malaysia: Tracing Energy Flows from Primary Source to End Use. Energies 2015, 8, 2828-2866.

Summary:

  • Sankey diagrams are used to visualize material and energy flows.
  • They show energy or material flows with arrows that are proportional to the amount
  • You have directional arrows
  • Sankey diagrams direct the viewer's gaze to the largest rivers or the largest consumers.
  • You communicate your message in an appealing way, both within the project team and externally.
  • There is no standard form or specification of how Sankey diagrams should look. There is a multitude of layout and design options.

Related topics:

Our software e! Sankey specializes in the creation of Sankey diagrams. The program is particularly well suited to visualize energy flows (energy flow diagrams, energy balances) and volume flows (mass / goods, value flows).