Sankey diagram framework for energy and exergy flows
Introduction
Sankey diagrams have been used as an effective tool to focus on energy flow and its distribution across various energy systems. It is represented by arrows, whose width represents the magnitude of the flow. Schmidt [1] presented a comprehensive review of the historical uses of Sankey diagrams stressing its rising importance in decision making and public policy. For example, the use of Sankey diagrams for identifying energy efficiency improvements for a society was addressed in a 1971 paper [2]. Many countries and international agencies have represented energy flows using Sankey diagrams from supply to end use sectors. International organizations such as ISO have developed energy management systems standards such as ISO 50001 (Energy Management Systems) to improve organizational energy performance. Such standards recognize the Sankey diagram as one of the tools that could be used in the energy review process that analyzes energy consumption, identifying significant consumption and identifying areas for improvements for energy performance planning [3, p. 14].
However, there is a lack of understanding on how such Sankey diagrams should be designed and developed for different applications and objectives. Issues such as the diagram’s structure (e.g. should flows be centered on processes, physical equipment, final energy services or a combination of these) and the appropriate level of detail and granularity are not fully addressed. Furthermore inconsistencies can be observed as to how energy losses are represented for various end-use products and services, showing a lack of consensus in how energy losses should be quantified for end-use products and services.
Representing energy losses for end-use products and services can be particularly challenging given that energy analysis does not support assessment of the quality and usefulness of energy. On the other hand, exergy analysis of energy systems and processes serves as a quantitative measure of quality and usefulness of energy [4]. Therefore, exergy flow Sankey diagrams can be very useful in identifying thermodynamic losses and potential areas for energy savings, and providing a rational basis for energy performance benchmarking, and for improving energy management systems and activities.
The purpose of this paper is to provide a framework to use energy and exergy flow Sankey diagrams for national level analysis. The remaining sections are organized as follows: Section 2 conducts a literature review of recent energy flow Sankey diagrams to identify and understand their features and differences. In Section 3, a framework matching key features of Sankey diagrams with different objectives of energy performance is presented. Section 4 explains the difference between energy balance and exergy balance, and provides a case study of UK’s industrial heating to show how and why exergy flow Sankey diagrams can be used in identifying potential energy savings. Section 5 concludes the paper.
Section snippets
Literature review of Sankey diagrams at national level
Although Sankey diagrams were originally developed to trace energy flows for steam engines, its application to energy flows in a society (e.g. at national and global level) has become increasingly important in recent years. This section conducts a review of the use of Sankey diagrams at the national level to identify and understand the features and differences of these Sankey diagrams, including system boundaries (both spatial and temporal), level of granularity, and representation of energy
Sankey framework for energy flow analysis at national level
National level analysis of energy systems are often performed under three categories of interests: energy economics, environmental impacts of energy, and energy security. Alternative classification of the objectives of analysis, such as increasing the use of alternative energy, and identifying areas for energy efficiency improvements and energy conservation have ramifications in all three categories mentioned above. These inter-linkages and inter-dependence of objectives make it challenging to
Exergy as a metric for loss representation
Sankey diagrams are often used to trace energy flows based on energy balance/conservation concepts and the First law of Thermodynamics. Under these principles, energy input and outputs at each stage of the energy system is balanced by considering the energy content of various sources and flows. Differences between magnitude of energy input and output are represented as losses only at relatively low levels of details and granularity (e.g. power generation losses, oil refining losses,
Conclusion
The matching of various key features with different objectives provides a framework for designing Sankey diagrams for national level and facility level analysis. The analysis makes three unique contributions to our understanding of how Sankey diagrams are to be designed for various objectives. Firstly, energy loss representations at low levels of granularity do not contribute significantly to energy performance objectives. Secondly, features based on refining sub-systems to trace energy use in
References (24)
- et al.
Oil development in China: current status and future trends
Energy Policy
(2012) - et al.
The efficient use of energy: tracing the global flow of energy from fuel to service
Energy Policy
(2010) - et al.
The use of energy in China: tracing the flow of energy from primary source to demand drivers
Energy
(2012) - et al.
Thermodynamic analysis of air-blown gasification for IGCC applications
Appl Energy
(2011) - et al.
Regional and global exergy and energy efficiencies
Energy
(1996) - et al.
Theoretical efficiency limits for energy conversion devices
Energy
(2010) - et al.
Exergy analysis of micro-organic Rankine power cycles for a small scale driven reverse osmosis desalination system
Appl Energy
(Apr 2010) The Sankey diagram in energy and material flow management
J Ind Ecol
(2008)The conversion of energy
Sci Am
(1971)- Draft International Standard ISO/DIS 50001 Energy management systems. International Organization for Standardization...
Chapter 2 – exergy and energy analyses, in EXERGY
Cited by (114)
A bibliometric examination and state-of-the-art overview of hydrogen generation from photoelectrochemical water splitting
2024, International Journal of Hydrogen EnergyEnvironmental optimization model for the European batteries industry based on prospective life cycle assessment and material flow analysis
2023, Renewable and Sustainable Energy ReviewsA supply chain allocation method for environmental responsibility based on fossil energy as the anchor for carbon responsibility
2023, Journal of Cleaner ProductionA bibliometric analysis of quality assurance in higher education institutions: Implications for assessing university's societal impact
2023, Evaluation and Program PlanningEnergy security performance evaluation revisited: From the perspective of the energy supply chain
2023, Renewable and Sustainable Energy Reviews