In view of the energy transition, it is important that engineering students are familiar with the concept of exergy and the added value of exergy analysis compared to energy analysis. Exergy analysis tells the truth about energy efficiency and exergy is directly related to sustainable development. This paper focuses on teaching exergy to students at the Delft University of Technology (TU Delft), but the contents are valuable to other engineering students as well. To encourage the teaching of exergy, the basics of exergy and exergy analysis are presented, as well as examples and ideas for teaching exergy to BSc students that are related to the topics of their BSc programme. It is recommended that the contents of this paper be discussed with many teachers of BSc programmes, especially teachers of BSc programmes that do not yet seem to include the teaching of exergy, and that attention be paid to teaching exergy to MSc students as well.@en

The Netherlands is known for its high penetration of natural gas use in households and industry, but the threat of climate change and earthquakes in the province of Groningen, caused by natural gas production, stimulate the search for alternatives, such as hydrogen gas. Various ways of producing and supplying hydrogen have the attention of scientists, companies and policy makers. This study compares the following three ways of green hydrogen production: 1) a photovoltaic system in Africa is used to produce hydrogen from sea water, followed by pipeline transport to Rotterdam, Netherlands, 2) electricity generated by the offshore Borssele 1&2 wind farm in the Netherlands is used for the offshore production of hydrogen from sea water followed by pipeline transport to Rotterdam, or 3) the electricity generated by this offshore wind farm is transmitted to Rotterdam where it is used for onshore production of hydrogen from sea water. The sustainability of the three systems is assessed from a life cycle point of view. The environmental LCA resulted in ReCiPe 2016 endpoint indicators and the midpoint indicators GWP, land use and water consumption. The exergetic sustainability assessment applied the Total Cumulative Exergy Loss (TCExL) method. The preferred system according to the results of the environmental LCA and the exergetic sustainability assessment is the wind energy system including offshore hydrogen production. The results are not unanimous as to which system is the second-best. The three systems need to be investigated in more detail before firm conclusions can be drawn. It is recommended that attention also be paid to the economic and social pillars of sustainability, and to the exergetic sustainability of technological systems in general, as exergetic assessment results are independent of changing and subjective models, weighting factors and other variables.@en

The intermittent nature of renewable energy sources like solar and wind energy stimulates the use of centralised and decentralised energy storage systems. The sustainability of lead acid, lithium-ion and concentration gradient flow batteries, compressed air and pumped hydro energy storage (PHES) systems is investigated by conducting a multi-dimensional life cycle assessment. The environmental, economic and exergetic sustainability are assessed by calculating ReCiPe 2016 indicators, the present worth ratio and the Total Cumulative Exergy Loss, respectively. The multi-dimensional sustainability assessment did not lead to one preferred system. The PHES causes the lowest damage to human health, ecosystem diversity and resource availability and results in the lowest global warming potential. The concentration gradient flow battery system named BBS is preferred from an economic viewpoint, while the PHES is second-best. The lithium-ion battery system causes the lowest exergy losses, followed by the PHES. It is recommended to pay attention to the exergetic sustainability of technological systems as exergy losses are independent of environmental models, weighting factors, market prices, subsidies etc. More research into the specifications of the energy storage systems is needed to be able to draw firm conclusions with regard to which system is preferred.

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Power generation from biomass is mentioned as a means to make our society more sustainable as it decreases greenhouse gas emissions of fossil origin and reduces the dependency on finite energy carriers, such as coal, oil and natural gas. When assessing the sustainability of power generation from biomass, it is important to consider the supply chain of the used biofuel by conducting a life cycle assessment of the system. Besides regular sustainability assessments, such as the calculation of the environmental sustainability, attention should be paid to exergy losses, i.e. the loss of 'energy quality', caused by the system as a whole, because every process and activity is accompanied with the loss of exergy and because the amount of exergy on earth can only be replenished by capturing new exergy from solar and tidal energy. This research compares the use of livestock manure and verge grass for power generation by assessing the systems from an environmental as well as an exergetic life cycle point of view. The assessed systems are the following: combustion of bioethanol from the fermentation of verge grass, combustion of substitute natural gas from anaerobic digestion of cow and pig manure and combustion of substitute natural gas from supercritical water gasification of cow and pig manure. The environmental sustainability is assessed by calculating ReCiPe endpoint indicators and the exergetic sustainability is assessed by applying the relatively new Total Cumulative Exergy Loss (TCExL) method. The TCExL method considers all exergy losses caused by a technological system during its life cycle, i.e. the internal exergy loss caused by the conversion of materials and energy, the abatement of emissions and the exergy loss related to land use. In addition to comparing the three systems as well as both assessment methods, the influence of taking into account the system's by-products as 'avoided products' and via 'allocation' on the assessment results is investigated. The bioethanol system appears more sustainable from an environmental sustainability point of view, while the bioethanol and supercritical water gasification systems are preferred from an exergetic sustainability point of view. The indicator of the environmental sustainability assessment is highly influenced by the way of taking into account by-products, while the exergetic sustainability indicator is not.@en

Energy conversion systems have assumed a crucial role in current society. The threat of climate change, fossil fuel depletion and the growing world energy demand ask for a more sustainable way of electricity production, eg, by using renewable energy sources, by improving the conversion efficiency and/or by controlling power plant emissions. Despite the relationship between exergy and sustainability stated in literature, exergy losses are usually not considered when comparing systems and energy sources for power generation. The exergetic sustainability assessment method named Total Cumulative Exergy Loss (TCExL) has been used to assess several systems for electricity production, ie, a coal-fired power plant, a coal-fired power plant including carbon capture and storage, a biomass-fired power plant, an offshore wind farm and a photovoltaic park. The results of the TCExL method have been compared with an environmental sustainability indicator, ie, the overall ReCiPe endpoint indicator and the economic indicator named Present Worth Ratio. The offshore wind farm is the best system from the exergetic and environmental point of view. The photovoltaic park is the system with the second-best scores. However, from the economic viewpoint including subsidy by the Dutch government, the photovoltaic park performs better than the wind farm system and the system that performs best is the biomass-fired power plant. Without subsidy, only the coal-fired power plant without carbon capture and storage is profitable. The exergetic sustainability scores of the coal-fired and biomass-fired power plants are similar, but from the environmental sustainability viewpoint, the biomass-fired power plant performs better than both coal-fired power plants. As the results of environmental and economic sustainability assessments strongly depend on models, weighting factors, subsidy, market prices, etc, while the results of the exergetic sustainability assessment do not, it is recommended that the exergetic sustainability be taken into account when assessing the sustainability of power generation and other technological systems.

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It is difficult to decide which power generation system is the most sustainable when environmental, economic and social sustainability aspects are taken into account. Problems with conventional environmental sustainability assessment methods are that no consensus exists about the applied models and weighting factors and that exergy losses are not considered. Economic sustainability assessment methods do not lead to results that are independent of time because they are influenced by market developments, while social sustainability assessment methods suffer from the availability and qualitative or semi-quantitative nature of data. Existing exergy analysis methods do not take into account all exergy losses and/or are extended with factors or equations that are not commonly accepted. The new Total Cumulative Exergy Loss (TCExL) method is based on fundamental thermodynamic equations and takes into account all exergy losses caused by a technological system during its life cycle, i.e. internal exergy losses, exergy losses caused by emission abatement and exergy losses related to land use. The development of the TCExL method is presented as well as the application of this method and environmental, economic and social sustainability assessment methods to two case studies: power generation in combination with LNG evaporation and Fossil versus renewable energy sources for power generation. According to the results of the assessments, large differences exist between the environmental sustainability assessment and TCExL methods in the sense that different parts of the systems contribute most to their overall scores. It is concluded from the case studies that involving the TCExL method in choices between power generation systems with the same energy sources has no consequences, i.e. it does not result in a different ranking of the systems, but can lead to the choice of a system that has a lower economic sustainability if the assessed systems use different energy sources. However, it must be noted that the economic sustainability changes over time, while the results of the TCExL method do not.

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The selection of power generation systems is important when striving for a more sustainable society. However, the results of environmental, economic and social sustainability assessments are subject to new insights into the calculation methods and to changing needs, economic conditions and societal preferences. Researchers active in the field of exergy and sustainability claim that exergy losses and sustainability are related. The Total Cumulative Exergy Loss method and the exergy replacement costs of minerals are used to assess and compare power generation systems that make use of fossil and renewable energy carriers. These power generation systems are the following: an ultrasupercritical coal power plant, a power plant that co-fires coal and biomass, a wind farm, and a combined cycle power plant that uses bioethanol originating from the fermentation of verge grass. Furthermore, environmental, economic and social sustainability assessment methods are applied to assess the four power generation systems as well. On the basis of the results of the assessments, it is concluded that the wind farm system is preferred from the environmental, social and exergetic sustainability points of view, but not from the economic sustainability viewpoint. The advantage of the exergetic sustainability assessment method is that its results are not influenced by choices like whether verge grass should be considered a waste product or not. The influence of the exergy replacement costs on the results of the exergetic assessment is small, because less than 5 per cent of the exergy input of the systems during construction, operation and commission is of mineral origin. When looking at the infrastructural part of the systems only, the influence of the exergy replacement costs is larger because about 25 to 40 per cent of the exergy input is of mineral origin. @en