Published on September 26, 2014
1 A Sankey Framework for Energy and Exergy Flows Kamalakannan (Kamal) Soundararajan Hiang Kwee Ho Bin Su Energy Studies Institute, National University of Singapore International Conference on Applied Energy (ICAE 2013) Pretoria, South Africa 1-4 July 2013
2 Sankey diagrams •An effective tool for representing energy flows •Not a new tool, developed over 100 years ago •Historically used to represent the energy or mass balances of complex technical systems •Increasingly it has been used to represent the energy flowing through a region, country or an aggregation of facilities
3 Source: Digest of United Kingdom Energy Statistics 2012
Sankey diagram (at a national level) 4
How can Sankey diagrams be designed for different applications and objectives? Some issues not fully addressed: •Structure of diagram (e.g. should flows be centred on processes, physical equipment, final energy services or a combination of these) •Appropriate level of detail and granularity 5
6 Key features and differences of Sankey diagrams for national level analysis •System Boundaries –Spatial and Temporal •Level of granularity –The extent an energy system is broken down (disaggregated) or refined •Representation of losses –e.g. transportation losses, distribution losses and transformation losses
Level of Granularity •Characterized by energy stages 7
Supply Stage •The primary energy supply stage (utilised energy resources) –usually classified into various types of fossil fuels and renewables with different levels of details –Other representations include sub stage division of the supply stage 8
Supply Stage 9 Source: R. E. . Sims and R. . Schock, “2007: Energy supply. In Climate Change 2007: Mitigation. Contribution of Working Group III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change.” 2007
Supply Stage 10 Source: L. Ma, F. Fu, Z. Li, and P. Liu, “Oil development in China: Current status and future trends,” Energy Policy, vol. 45, no. 0, pp. 43–53, Jun. 2012.
Transformation Stage •energy transformation stage broadly refers to energy resources being converted to energy carriers and secondary forms of energy supply –E.g. of power generation and oil refineries –Representation of transmission and distribution sub stages 11
Transformation Stage 12
Transformation Stage 13 Source: L. Ma, F. Fu, Z. Li, and P. Liu, “Oil development in China: Current status and future trends,” Energy Policy, vol. 45, no. 0, pp. 43–53, Jun. 2012.
Consumption Stage •energy consumption stage incorporates the various activities and flows associated with final energy use and consumption to provide desired energy services to the energy user who uses them to produce useful products and services –Represented as demand sectors/energy intensive sub sectors (e.g. Transport, commercial, petrochemicals or iron & steel) –Represented as energy services (e.g. transportation, lighting, space heating or final manufactured products) –Sub-stages represented as end-use energy conversion (e.g. Boilers, lighting devices, motors or chillers) 14
Consumption Stage represented as demand sectors 15
16 Source: Energy Technology Perspectives 2012 Consumption Stage represented in sub stages
Energy loss representation •Primary energy conversion losses during the transformation stage –Electricity generation –Refining •Transport and distribution losses •Losses that result from converting renewable/alternative resources to electricity and non electricity carriers –Insufficient distinction made between resources and carriers at the supply and transformation stages •Within the consumption stage losses are generally not represented –Difficulties faced in defining and identifying various loss mechanisms –Lack of detailed data to quantify such losses 17
•No single Sankey diagram representation is able to fulfil all the objectives of energy analysis at a national level •Alignment of objectives with key features of Sankey diagrams can offer an effective approach to the design and utilization of Sankey diagrams 18 Sankey framework for national level analysis
•Public Awareness (making the common people aware of energy issues and enhancing their ability to contribute directly to national energy challenges and needs) •Security of supply (security of domestic supply of energy resources or carriers entering the energy system) •Increasing the use of alternative/renewable energy •Identifying areas for energy savings –Energy efficiency improvements –Energy conservation 19 National level objectives
20 Key features Public awareness Security of supply Increasing the use of alternative energies Identifying areas for energy savings Energy efficiency improvements Energy conservation General Features 1. Colour coded and labelled energy flows Features based on national boundaries 1.Differentiation of energy resources and their associated carriers 2. Representation of import and export flows of energy resources and carriers 3. Representation of stock exchange and storage flows 4. Representation of important energy intensive sectors (at the transformation stage) 5. Tracing of energy supply to various consumption sectors (represents energy intensive sectors separately) 6. Identifies energy losses in energy transformation, transport and distribution separately 7. Boundary of energy system focused on consumption of energy without differentiating imports and exports Features based on refining representation to trace energy use in various conversion devices, products and services 1.Tracing alternative energy resources to various energy carriers (including conversion losses) 2. Boundary of energy system focused on the industrial sector 3. Boundary of energy system focused on the transport/building sector
Exergy flow as a useful tool in national level analysis •Representing energy losses within the consumption stage, based on energy balances has various limitations (e.g. quality of work associated with different forms of energy) •Unlike energy, exergy is not conserved •Exergy destruction provides an excellent quantifiable indication of where and how losses occur. 27
Overlaying energy with exergy flow diagrams 28
Concluding remarks •Energy loss representation at low levels of granularity do not contribute significantly to energy performance objectives •Features based on refining sub-systems to trace energy use in various conversion devices, products and services provides additional insights to energy performance objectives •Overlaying energy and exergy Sankey diagrams provides a possible alignment of how energy losses are calculated and represented, identifying potential areas for energy performance improvements. 29
Thank you 30
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