A Primer on Energy Flow Diagrams
Energy Flow Diagrams (often also referred to as Energy Flow Charts) are used to show energy and energy transformation visually and quantitatively. This may include primary energy used as raw fuels to feed into a system, energy supply, conversion or transformation, losses and energy being used.
These are the types of energy flow diagrams we find most:
- energy flow chart of a country (national energy balance)
- energy flows in a region
- corporate energy flows (in a company, site or plant)
- energy streams in a technical process
They are mostly presented as Sankey diagrams, where the width of an arrow represents the energy quantity. All flows typically use the same unit of measurement, such as kWh, MWh, PJ, BTU, or Mtoe. If various types of energy are displayed, this is normally done with different colors.
Energy Flow Chart for a Country
Probably the most famous energy flow charts are the ones produced by Lawrence Livermore National Laboratories (LLNL). They are available for the United States (and for all states individually) and for many other countries (see here). The one shown here is for the U.S. 2017, the unit of measurement is 'Quads'.
The energy flow diagram shows, on the left side, the fuels (primary energy) as sources. Streams lead to energy generation (power plants) or directly to the consuming sectors on the right (industry, commercial, residential, transportation). 'Rejected energy' (losses) are shown in grey color and contrasted with 'Energy services' (useful energy).
Data for national energy flow charts are typically from statistics offices. In the case presented here the Department of Energy (DOE) compiles the data every year.
Regional Energy Flows
States, regions, and communities take initiative and also present diagrams of their energy flows. With technologies such as micro grid, and an increasing trend for local, decentralized energy generation they document transparently where energy is sourced, how it was created, and who is using it. One particular aspect of regional energy flow charts are imports and exports of energy across administrative boundaries of the region considered.
Local actors use these visualizations to create awareness in the community for the energy topic, and to endorse alternative energy systems, often based on renewables.
In France there are a number of local energy and climate agencies (Agences Locales de l’Énergie et du Climat) that coordinate regional activities. They also publish energy flows diagrams, like this one from the Nouvelle-Acquitaine region in the South-West of the country. Image courtesy AREC-NA, image from their internet site www.arec-nouvelleaquitaine.com
Energy Flows in a Company
Companies in different industrial sectors, are setting up energy management systems according to ISO 50001. Within the framework of this management system they are also measuring and analyzing energy consumption at the production site or plant. This is another typical use case for energy flow diagrams (Sankey diagrams).
The diagrams serve to support internal communication (e.g. analysis and discussion with in the energy team), but also as documentation (e.g. to prepare for an energy audit) and for presentations to external stakeholders.
The figure shows a typical corporate energy flow diagram (although with fictitious values). On the left we can see the total energy supply per year, broken down into the different fuels purchased. On the right we can see the consumers and their share of the energy use. According to the ISO 50006 standard the EnPI energy use per revenue is used exemplarily.
Energy Flow in a Process
Energy flow diagrams are also a great tool to trace energy losses within a production line or a technical process. They help identifying at which stage losses occur.
In this sample energy flows are shown for the generation of natural gas out of biomass (wood). The chart shows precisely how the process heat is re-used.
Energy Flow Charts are often shown as Sankey Diagrams.
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Several examples files shipped in e!Sankey show Sankey diagrams from energy management, like the one above. Download your e!Sankey trial version free-of-charge now.