Energy Flow Sankey Diagram: How to Build and Read One
How to draw an energy flow Sankey diagram: sources, conversion, losses and end use, why losses are a ribbon, and an editable example with invented figures.
An energy flow Sankey follows energy from fuel to use and shows what is lost on the way. It is the diagram the form was invented for.
Energy is conserved, so what goes into a conversion step comes out again as useful energy plus losses, usually heat. A Sankey diagram makes that visible: the loss is a band, as wide as it is, instead of a number in a table.
The example is a small power and heat plant with invented figures: 100 units of fuel go in, 40 leave as electricity and 45 as heat, and 15 are lost. The useful outputs then go to industry and homes.
How to structure it
Put the sources on the left, the conversion equipment next, then the carriers (electricity, heat) and losses, and finally the end uses. Use one unit throughout, such as kWh or joules, and a defined boundary, for example one building, one plant or one country.
Why losses get a band
Without a losses node the plant's bands would not add up. With it, the diagram balances and the efficiency is visible: 85 of 100 units leave as useful energy here.
Use real data and say where it came from
The example is invented. For a real diagram take metered or published figures, state the year and the boundary, and cite the source. A Sankey diagram presents energy data; it is not an energy audit and does not meet any reporting standard on its own.
Key points
- 100 units of fuel become 85 units of electricity and heat and 15 of losses: an efficiency of 85% in this example.
- Heat is the larger output (45) and all of it goes to homes.
- Electricity splits evenly between industry and homes.
- The figures are invented.
The example’s data
Invented figures in arbitrary energy units. Not data about any real plant.
| From | To | Amount (units of energy) |
|---|---|---|
| Fuel | Power and heat plant | 100 |
| Power and heat plant | Electricity | 40 |
| Power and heat plant | Heat | 45 |
| Power and heat plant | Losses | 15 |
| Electricity | Industry | 20 |
| Electricity | Homes | 20 |
| Heat | Homes | 45 |
The same data as CSV
source,target,value
Fuel,Power and heat plant,100
Power and heat plant,Electricity,40
Power and heat plant,Heat,45
Power and heat plant,Losses,15
Electricity,Industry,20
Electricity,Homes,20
Heat,Homes,45How it works
Draw the boundary
Decide what is inside the diagram and for which period.
Add the conversions and their losses
For each piece of equipment, add flows to its outputs and a flow to a losses node.
Check conservation
Energy in must equal energy out plus losses at every node.
Frequently asked questions
Why do energy Sankey diagrams often have a lot of losses?
Because conversions such as burning fuel to make electricity lose a large share as heat. The diagram makes the share visible.
Can I use it for compliance?
Not by itself. It presents data you have compiled and documented. Reporting standards need their own method and evidence.
Edit this energy Sankey
Open the example as your own chart and enter your sources and uses.