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This paper investigates how the heating sector can best support the green transition into climate-neutral societies. In order to do so, the heating sector must be considered and analysed as an integral part of the entire energy system as well as be coordinated with other greenhouse gas emitting sectors. Consequently, in this study with Denmark as a case, we establish the context of a full transition of all sectors into a climate-neutral society. Using such context, we investigate the role of the heating sector with a focus on excess heat potentials, energy savings vs. supply, district heating vs. individual heating as well as the ability to recycle low-temperature excess heat and to provide flexibility and support the integration of variable renewable energy sources also in other subsectors of the energy system. The results of the analyses show (1) a feasible reduction level of around 36% in end-use heat demand in buildings, with higher potential in older buildings and lower in new buildings, (2) expanding district heating to areas with a density of 15-10 kWh/m² is feasible, resulting in a district heating share of 63-70% of the heat demand compared to the current level of 51%, (3) a large unexploited potential to use heat sources such as industrial excess heat, geothermal heat, data centres and power-to-X, reducing the need for biomass in the heating sector, and (4) increased use of variable renewable energy and combined heat and power production increasing gas export and thus replacing biomass consumption outside the country. [ABSTRACT FROM AUTHOR]

At the local level, energy communities are at the forefront of the European Green Deal strategy offering new opportunities for citizens to get actively involved in energy markets. The scope of this study is to apply a multi-objective optimization framework to minimize both carbon dioxide emissions and total annual costs in an energy community, considering, within different constraints, a wide availability of decision variables including local renewable energy sources, sector coupling, storage and hydrogen. The methodology involves the coupling of the software EnergyPLAN with a multi-objective evolutionary algorithm, considering 2030 and 2050 as target years and modelling a set of eight types of scenarios, each consisting of 100 optimal systems out of 10,000. The case study is an energy community in the European Alps. The results show, on the one hand, the key role of sector coupling technologies such as cogeneration, heat pumps and electric vehicles in exploiting local renewable energy sources and, on the other hand, the higher costs in introducing both electricity storage to achieve a complete decarbonisation and hydrogen as an alternative strategy in the electricity, thermal and transport sectors. More specifically, it has been identified that, by 2030 a complete decarbonisation cannot be achieved considering the replacement rates of the technologies included in the Baseline 2018, but nevertheless the European target of -55% of CO2 emissions can be reached with costs similar to those of the Business As Usual trajectory, while, by 2050 a complete decarbonisation is possible with costs within 24% higher than those of the Business As Usual trajectory. [ABSTRACT FROM AUTHOR]

Moving towards carbon-neutral societies, both nuclear and renewable energy can potentially supply CO 2 -free electricity. While the cost of renewable energy has decreased significantly, the cost of nuclear has, however, increased in the past decades and now in general exceeds the cost of renewables. However, one cannot compare directly the per unit cost of electricity since temporal behavior in the electricity production differs substantially between the two groups of technologies. Nuclear power inherently aims to provide a constant base load supply of electricity, while renewables generally depend on weather patterns. Thus, the two have different requirements and impact the overall system costs differently regarding flexibility and system design. Focusing on the case of Denmark, this article investigates a future fully sector-coupled energy system in a carbon-neutral society and compares the operation and costs of renewables and nuclear-based energy systems. The study finds that investments in flexibility in the electricity supply are needed in both systems due to the constant production pattern of nuclear and the variability of renewable energy sources. However, the scenario with high nuclear implementation is 1.2 billion EUR more expensive annually compared to a scenario only based on renewables, with all systems completely balancing supply and demand across all energy sectors in every hour. For nuclear power to be cost competitive with renewables an investment cost of 1.55 MEUR/MW must be achieved, which is substantially below any cost projection for nuclear power. • Both renewable energy and nuclear power benefits from sector coupling. • Hourly modelling is required to capture system effects. • Nuclear systems require less flexibility capacity than renewable only systems. • A renewable energy system is cheaper than a nuclear based system. • Lower flexibility costs do not offset the high investment costs in nuclear energy. [ABSTRACT FROM AUTHOR]

This editorial introduces the 31st volume of the International Journal of Sustainable Energy Planning and Management. This volume reports some of the latest developments in energy systems analyses of smart energy systems and of district heating as well as in methods and analyses using multi-objective optimisation. In one of the analyses, the authors investigate the effects of decentralised storage in district heating systems, finding positive effects on grid design as the impact of peaks can be reduced. Three contributions address the more sociological factors influencing acceptance and energy system development such as ownership, awareness, and moral. [ABSTRACT FROM AUTHOR]

Abstract This paper provides a perspective on the development of future district heating systems and technologies and their role in future smart energy systems. The reviewed papers elaborate on or otherwise contribute to the theoretical scientific understanding of how we can design and implement a suitable and least-cost transformation into a sustainable energy future. Focus is on the important role of the next generation of district heating and cooling technologies. The status of the scientific contributions demonstrates a high level of understanding of how to deal with the technical aspects. The primary current challenge seems to be the understanding of the implementation of these. Highlights • A transformation into low-temperature becomes essential for future district heating. • High level of understanding of how to deal with the technical aspects. • Primary current challenge seems to be the understanding of the implementation. [ABSTRACT FROM AUTHOR]

Abstract This paper presents a new method, based on the Smart Energy Systems concept. The aim is to increase the share of renewable energy penetration on islands. The method is applied to the island of Gran Canaria (Spain), considering the entire energy system of the island. Several smart renewable energy strategies are proposed following a cross-sectoral approach between the electricity, heating/cooling, desalination, transport and gas sectors. The different smart renewable energy strategies were applied in a series of steps, while looking for a transition from the current energy system to a nearly 100% renewable energy system. Based on the results, the study concludes that the suggested method is applicable for increasing renewable integration on islands and can potentially be used in helping energy planners to take decisions about priorities in development of the sector to improve such integration. The results indicate that, for the case of Gran Canaria, a 75.9% renewable energy system could be attained with technologies that can be implemented at present. Furthermore, it is shown that a nearly 100% renewable energy system in Gran Canaria is technically feasible and could be achieved if certain technologies acquire greater maturity. Highlights • A new Smart Renewable Energy approach for islands is presented. • A cross-sectoral method is proposed to increase the renewable energy on islands. • A new strategy is used to select the optimal energy configuration for each scenario. • The more demand becomes manageable, the more the proposed method increases PV power. [ABSTRACT FROM AUTHOR]

In recent years, the terms “Smart Energy” and “Smart Energy Systems” have been used to express an approach that reaches broader than the term “Smart grid”. Where Smart Grids focus primarily on the electricity sector, Smart Energy Systems take an integrated holistic focus on the inclusion of more sectors (electricity, heating, cooling, industry, buildings and transportation) and allows for the identification of more achievable and affordable solutions to the transformation into future renewable and sustainable energy solutions. This paper first makes a review of the scientific literature within the field. Thereafter it discusses the term Smart Energy Systems with regard to the issues of definition, identification of solutions, modelling, and integration of storage. The conclusion is that the Smart Energy System concept represents a scientific shift in paradigms away from single-sector thinking to a coherent energy systems understanding on how to benefit from the integration of all sectors and infrastructures. [ABSTRACT FROM AUTHOR]

In recent years, several tools and models have been developed and used for the design and analysis of future national energy systems. Many of these models focus on the integration of various renewable energy resources and the transformation of existing fossil-based energy systems into future sustainable energy systems. The models are diverse and often end up with different results and recommendations. This paper analyses this diversity of models and their implicit or explicit theoretical backgrounds. In particular, two archetypes are defined and compared. On the one hand, the prescriptive investment optimisation or optimal solutions approach. On the other hand the analytical simulation or alternatives assessment approach. Awareness of the dissimilar theoretical assumption behind the models clarifies differences between the models, explains dissimilarities in results, and provides a theoretical and methodological foundation for understanding and interpreting results from the two archetypes. [ABSTRACT FROM AUTHOR]

In the transition to renewable energy systems, fluctuating renewable energy, such as wind and solar power, plays a large and important role. This creates a challenge in terms of meeting demands, as the energy production fluctuates based on weather patterns. To utilise high amounts of fluctuating renewable energy, the energy system has to be more flexible in terms of decoupling demand and production. This paper investigates two potential ways to increase flexibility. The first is the interconnection between energy systems, for instance between two countries, labelled as cross-border interconnection, and the second is cross-sector interconnection, i.e., the integration between different parts of an energy system, for instance heat and electricity. This paper seeks to compare the types of interconnectivity and discuss to which extent they are mutually beneficial. To do this, the study investigates two energy systems that represent Northern and Southern Europe. Both systems go through three developmental steps that increase the cross-sector interconnectivity. At each developmental step an increasing level of transmission capacities is examined to identify the benefits of cross-border interconnectivity. The results show that while both measures increase the system utilisation of renewable energy and the system efficiency, the cross-sector interconnection gives the best system performance. To analyse the possible interaction between cross-sector and cross-border interconnectivity, two main aspects have to be clarified. The first part defines the approach and the second is the construction of the two archetypes. [ABSTRACT FROM AUTHOR]

In the transition to renewable energy systems, national plans are being created for several countries around the world. Concurrently, regions, municipalities and cities are planning for CO 2 neutral and renewable energy systems. Both developments are necessary, which raises the question whether these two types of energy planning are coordinated. How should national plans specify local actions, and how should local plans take into account the surrounding development of the energy system? Most local plans rely on the surrounding energy systems as they need to integrate with the energy system to export excess production or import during demands with insufficient capacity. This paper suggests a methodology to analyse how well these local plans integrate with the surrounding national energy system. The methodology is applied to the two Danish examples of Copenhagen and Sønderborg. Both examples connect to the Danish 2030 scenario defined in the Coherent Energy and Environmental System Analysis study. Based on the results the study concludes that the suggested methodology is applicable for evaluating how well local and national energy systems integrate, and can potentially be used in bettering energy planning to include the benefits of local action and national coordination. [ABSTRACT FROM AUTHOR]

This editorial gives an introduction to the important relationship between Smart Energy Systems and 4th Generation District Heating and presents a number of selected papers from the 1st International Conference on the topic. All of the papers elaborate on or otherwise contribute to the theoretical scientific understanding on how we can design and implement a suitable and least-cost transformation into a sustainable energy future. The concept of Smart Energy Systems emphasizes the importance of being coherent and cross-sectoral when the best solutions are to be found and how this also calls for the active inclusion of the heating and cooling sectors. The concept of 4th Generation District Heating emphasizes that district heating and cooling are both important elements but also technologies that have to be developed further into a 4th generation version to be able to fulfil their roles in future sustainable energy systems. The conclusion is that further development of such theoretical scientific understanding is essential for the implementation of political goals related to future sustainable energy solutions. [ABSTRACT FROM AUTHOR]

In the transition towards a 100% renewable energy system, energy savings are essential. The possibility of energy savings through conservation or efficiency increases can be identified in, for instance, the heating and electricity sectors, in industry, and in transport. Several studies point to various optimal levels of savings in the different sectors of the energy system. However, these studies do not investigate the idea of energy savings being system dependent. This paper argues that such system dependency is critical to understand, as it does not make sense to analyse an energy saving without taking into account the actual benefit of the saving in relation to the energy system. The study therefore identifies a need to understand how saving methods may interact with each other and the system in which they are conducted. By using energy system analysis to do hourly simulation of the current Danish energy system, the combination of reductions in heat and electricity demands is analysed within the Danish district heating sector to show the benefits of coordinating savings in the electricity and district heating sectors. [ABSTRACT FROM AUTHOR]

Intermittent renewable energy sources (RES) are increasingly used in many energy systems. The higher capacity of intermittent RES increases the importance of introducing flexible generation units into the electricity system balancing. Distributed district heating plants with combined heat and power (CHP) can provide this flexibility. However, in electricity systems with a high penetration of intermittent RES, CHP units are currently experiencing decreasing hours of operation, making it likely that existing CHP capacity will be phased out from the energy system. Furthermore, when the plants provide balancing for the electricity system, the complexity of their daily operation planning is increased. This article analyses and discusses how these units can improve their economic feasibility by providing balancing services to the electricity system, benefitting both each individual plant and the system as a whole. This is done by using the case of the Danish district heating plant, Ringkøbing District Heating, which has a relatively high capacity of solar heating installed and is located in an area with a high penetration of wind power. It is found that the plant can increase the economic feasibility of the CHP unit by participating in the electricity balancing tasks; however, it is uncertain whether the benefits are substantial enough to keep the distributed CHP capacity in operation. [ABSTRACT FROM AUTHOR]

Abstract: This paper defines the concept of 4th Generation District Heating (4GDH) including the relations to District Cooling and the concepts of smart energy and smart thermal grids. The motive is to identify the future challenges of reaching a future renewable non-fossil heat supply as part of the implementation of overall sustainable energy systems. The basic assumption is that district heating and cooling has an important role to play in future sustainable energy systems – including 100 percent renewable energy systems – but the present generation of district heating and cooling technologies will have to be developed further into a new generation in order to play such a role. Unlike the first three generations, the development of 4GDH involves meeting the challenge of more energy efficient buildings as well as being an integrated part of the operation of smart energy systems, i.e. integrated smart electricity, gas and thermal grids. [Copyright &y& Elsevier]

Abstract: The utilisation of biomass poses large challenges in renewable energy systems while buildings account for a substantial part of the energy supply even in 100% renewable energy systems. In this paper the focus is on how the heating sector can reduce its consumption of biomass, thus leaving biomass for other sectors, but while still enabling a 100% renewable energy system. The analyses of heating technologies shows that district heating (DH) systems are important in limiting the dependence on biomass and create cost effective solutions. DH systems are especially important in renewable energy systems with large amounts of fluctuating sources as it enables fuel efficient and low cost energy systems with thermal heat storages. DH increases the efficiency with the use of combined heat and power production (CHP), while reducing the biomass demand by enabling the use of other renewable resources such as large-scale solar thermal, large heat pumps, geothermal heat, industrial surplus heat, and waste incineration. Where the energy density in the building stock is not high enough for DH to be economical, geothermal heat pumps can be recommended for individual heating systems, even though biomass consumption is higher than the DH solutions. [Copyright &y& Elsevier]

Abstract: This paper presents the results of adding a CCS(Carbon Capture and Storage) plant including an underground CO2 storage to a well described and well documented vision of converting the present Danish fossil based energy system into a future sustainable energy system made by the Danish Society of Engineers. The analyses point in the direction that in such context a CCS investment is not a suitable way to decrease CO2 emissions. Other alternatives are more cost effective and will fit better into the long-term implementation of sustainable energy systems. The reason is that CCS investments involve huge construction costs with the expectation of long lifetimes. Consequently, the CCS has to operate as part of large-scale power or CHP plants with high utilisation hours for the CCS investment to come even close to being feasible. However, seen in the light of transforming to sustainable energy systems, the number of utilisation hours of power and CHP plants will have to decrease substantially due to the energy efficiency measures in combination with the inclusion of renewable energy power inputs from wind and similar resources. Consequently, no power or CHP plants exist in future sustainable energy systems with sufficient utilisation hours to justify a CCS plant. [Copyright &y& Elsevier]

Abstract: This paper presents Concrete Institutional Economics as an economic paradigm to understand how the wish for sustainable energy in times of economic crisis can be used to generate jobs as well as economic growth. In most countries, including European countries, the USA and China, the implementation of sustainable energy solutions involves the replacement of imported fossil fuels by substantial investments in energy conservation and renewable energy (RE). In such situation, it becomes increasingly essential to develop economic thinking and economic models that can analyse the concrete institutions in which the market is embedded. This paper presents such tools and methodologies and applies them to the case of the Danish heating sector. The case shows how investments in decreasing fossil fuels and CO2 emissions can be made in a way in which they have a positive influence on job creation and economic development as well as public expenditures. [Copyright &y& Elsevier]

Abstract: The challenge of integrating fluctuating power from renewable energy sources in the electricity grid by the use of smart grids cannot be looked upon as an isolated issue but should be seen as one out of various means and challenges of approaching sustainable energy systems in general. Therefore, electricity smart grids must be coordinated with the utilisation of renewable energy being converted into other forms of carriers than electricity including heat and biofuels as well as energy conservation and efficiency improvements, such as CHP and improved efficiencies e.g. in the form of fuel cells. All such measures have the potential to replace fossil fuels or improve the fuel efficiency of the system. However, they also add to the electricity balancing problem and contribute to the excess electricity production and thereby to the need for electricity smart grids. The long-term relevant systems are those in which such measures are combined with energy conservation and system efficiency improvements. This article illustrates why electricity smart grids should be seen as part of overall smart energy systems and emphasises the inclusion of flexible CHP production in the electricity balancing and grid stabilisation. Furthermore, it highlights some recent developments in the Danish electricity market operation. [Copyright &y& Elsevier]

Abstract: This paper presents a model of the Romanian energy system with the purpose of providing a tool for the analysis of future sustainable energy strategies. The model represents the total national energy system and is detailed to the level of hourly demand and production in order to be able to analyse the consequences of adding fluctuating renewable energy sources to the system. The model has been implemented into the EnergyPLAN tool and has been validated in order to determine if it can be used as a reference model for other simulations. In EnergyPLAN, two different future strategy scenarios for the Romanian energy system are compared to the actual data of Romania of year 2008. First, a comparison is made between the 2008 model and the 2013 strategy scenario corresponding to the grid of the Romanian transmission system operator (TSO) Transelectrica. Then, a comparison is made to a second strategy scenario in which the installed nuclear capacity is reduced by 50%. [Copyright &y& Elsevier]

Abstract: This paper presents the ability of the existing Chinese energy system to integrate wind power and explores how the Chinese energy system needs to prepare itself in order to integrate more fluctuating renewable energy in the future. With this purpose in mind, a model of the Chinese energy system has been constructed by using EnergyPLAN based on the year 2007, which has then been used for investigating three issues. Firstly, the accuracy of the model itself has been examined and then the maximum feasible wind power penetration in the existing energy system has been identified. Finally, barriers have been discussed and suggestions proposed for the Chinese energy system to integrate large-scale renewable energy in the future. It is concluded that the model constructed by the use of EnergyPLAN can accurately simulate the Chinese energy system. Based on current regulations to secure grid stability, the maximum feasible wind power penetration in the existing Chinese energy system is approximately 26% from both technical and economic points of view. A fuel efficiency decrease occurred when increasing wind power penetration in the system, due to its rigid power supply structure and the task of securing grid stability, was left primarily to large coal-fired power plants. There are at least three possible solutions for the Chinese energy system to integrate large-scale fluctuating renewable energy in the long term: Redesigning the regulations to secure grid stability by means of diversifying the participants, such as including hydropower and CHP plants; integrating large-scale heat pumps combined with heat storage devices to satisfy district heat demands and developing electric vehicles to promote off peak electricity utilisation. [Copyright &y& Elsevier]

Abstract: Along with high-speed economic development and increasing energy consumption, the Chinese Government faces a growing pressure to maintain the balance between energy supply and demand. In 2009, China has become both the largest energy consumer and CO2 emitting country in the world. In this case, the inappropriate energy consumption structure should be changed. As an alternative, a suitable infrastructure for the implementation of renewable energy may serve as a long-term sustainable solution. The perspective of a 100% renewable energy system has been analyzed and discussed in some countries previously. In this process, assessment of domestic renewable energy sources is the first step. Then appropriate methodologies are needed to perform energy system analyses involving the integration of more sustainable strategies. Denmark may serve as an example of how sustainable strategies can be implemented. The Danish system has demonstrated the possibility of converting into a 100% renewable energy system. This paper discusses the perspective of renewable energy in China firstly, and then analyses whether it is suitable to adopt similar methodologies applied in other countries as China approaches a renewable energy system. The conclusion is that China’s domestic renewable energy sources are abundant and show the possibility to cover future energy demand; the methodologies used to analyse a 100% renewable energy system are applicable in China. Therefore, proposing an analysis of a 100% renewable energy system in China is not unreasonable. [ABSTRACT FROM AUTHOR]

Abstract: Greenhouse gas mitigation strategies are generally considered costly with world leaders often engaging in debate concerning the costs of mitigation and the distribution of these costs between different countries. In this paper, the analyses and results of the design of a 100% renewable energy system by the year 2050 are presented for a complete energy system including transport. Two short-term transition target years in the process towards this goal are analysed for 2015 and 2030. The energy systems are analysed and designed with hour-by-hour energy system analyses. The analyses reveal that implementing energy savings, renewable energy and more efficient conversion technologies can have positive socio-economic effects, create employment and potentially lead to large earnings on exports. If externalities such as health effects are included, even more benefits can be expected. 100% Renewable energy systems will be technically possible in the future, and may even be economically beneficial compared to the business-as-usual energy system. Hence, the current debate between leaders should reflect a combination of these two main challenges. [ABSTRACT FROM AUTHOR]

Abstract: The Danish city Frederikshavn is aiming at becoming a 100% renewable energy city. The city has a number of energy resources including a potential for off-shore wind power, waste and low-temperature geothermal energy usable as heat source for heat pumps producing district heating. In this article, a technical scenario is described and developed for the transition of Frederikshavn’s energy supply from being predominantly fossil fuelled to being fuelled by locally available renewable energy sources. The scenario includes all aspects of energy demand in Frederikshavn i.e. electricity demand, heat demand, industrial demand as well as the energy demand for transportation. The locally available energy resources are deliberated and an energy system is designed and analysed with an energy systems analysis model on an aggregate annual level as well as on an hourly basis. Particular attention is given to the use of geothermal energy in the area. It is shown, that the use of geothermal energy in combination with an absorption heat pump shows promise in a situation where natural gas supply to conventional cogeneration of heat and power (CHP) plants decreases radically. [ABSTRACT FROM AUTHOR]

Abstract: Replacing individual natural gas heating with district heating based to increasing shares of renewable energy sources may further reduce CO2-emissions in the Danish Building mass, while increasing flexibility of the energy system to accommodate significantly larger amounts of variable renewable energy production. The present paper describes a geographical study of the potential to expand district heating into areas supplied with natural gas. The study uses a highly detailed spatial database of the built environment, its current and potential future energy demand, its supply technologies and its location relative to energy infrastructure. First, using a spatially explicit economic model, the study calculates the potentials and costs of connection to expanded district heating networks by supply technology. Then a comprehensive energy systems analysis is carried out to model how the new district heat can be supplied from an energy system with higher shares of renewable energy. It can be concluded on the basis of these analyses that the methods used proved highly useful to address issues of geographically dependent energy supply; however the spatio-economic model still is rather crude. The analyses suggest to expand district heating from present 46% to somewhere in between 50% and 70%. The most attractive potential is located around towns and cities. The study also suggests that CO2-emissions, fuel consumption and socio-economic costs can be reduced by expanding district heating, while at the same time investing in energy savings in the building mass as well as increased district heating network efficiency. [Copyright &y& Elsevier]

Background, aim and scope This paper discusses the identification of the environmental consequences of marginal electricity supplies in consequential life cycle assessments (LCA). According to the methodology, environmental characteristics can be examined by identifying affected activities, i.e. often the marginal technology. The present 'state-of theart' method is to identify the long-term change in power plant capacity, known as the long-term marginal technology, and assume that the marginal supply will be fully produced at such capacity. However, the marginal change in capacity will have to operate as an integrated part of the total energy system. Consequently, it does not necessarily represent the marginal change in electricity supply, which is likely to involve a mixture of different production technologies. Especially when planning future sustainable energy systems involving combined heat and power (CHP) and fluctuating renewable energy sources, such issue becomes very important. Materials and methods This paper identifies a business-asusual (BAU) 2030 projection of the Danish energy system. With a high share of both CHP and wind power, such system can be regarded a front-runner in the development of future sustainable energy systems in general. A strict distinction is made between, on the one hand, marginal capacities, i.e. the long-term change in power plant capacities, and on the other, marginal supply, i.e. the changes in production given the combination of power plants and their individual marginal production costs. Detailed energy system analysis (ESA) simulation is used to identify the affected technologies, considering the fact that the marginal technology will change from one hour to another, depending on the size of electricity demand compared to, among others, wind power and CHP productions. On the basis of such input, a long-term yearly average marginal (YAM) technology is identified and the environmental impacts are calculated using data from ecoinvent. Results The results show how the marginal electricity production is not based solely on the marginal change in capacity but can be characterised as a complex set of affected electricity and heat supply technologies. A longterm YAM technology is identified for the Danish BAU2030 system in the case of three different long-term marginal changes in capacity, namely coal, natural gas or wind power. Discussion Four analyses and examples of YAMs have been used in order to present examples of the cause-effect chain between a change in demand for electricity and the installation of new capacity. In order to keep open the possibilities for further analysis of what can be considered the marginal technology, the results of four different situations are provided. We suggest that the technology mix with the installation of natural gas or coal power plant is applied as the marginal capacity. Conclusions The environmental consequences of marginal changes in electricity supply cannot always be represented solely by long-term change in power plant capacity, known as the long-term marginal technology. The marginal change in capacity will have to operate as an integrated part of the total energy system and, consequently, in most energy systems, one will have to identify the long-term YAM technology in order to make an accurate evaluation of the environmental consequences. Recommendations and perspectives This paper recommends a combination of LCA and ESA as a methodology for identifying a complex set of marginal technologies. The paper also establishes values for Danish marginal electricity production as a yearly average (YAM) that can be used in future LCA studies involving Danish electricity. [ABSTRACT FROM AUTHOR]

Future sustainable energy systems call for the introduction of integrated storage technologies. One of these technologies is compressed air energy storage (CAES). In Denmark at present, wind power meets 20% and combined heat and power production (CHP) meets 50% of the electricity demand. Based on these figures, the paper assesses the value of integrating CAES into future sustainable energy systems with even higher shares of fluctuating renewable energy sources. The evaluation is made on the basis of detailed energy system analyses in which the supply of complete national energy systems is calculated hour by hour in relation to the demands during a year. The Danish case is evaluated in a system-economic perspective by comparing the economic benefits achieved by improving the integration of wind power to the costs of the CAES technology. The result is compared to various other storage options. Furthermore, a business-economic evaluation is done by calculating the potential income of the CAES technology from both spot markets and regulating power markets. The evaluation includes both historical hour by hour prices during a 7-year period on the Nordic Nord Pool market as well as expected future price variations. The conclusion is that even in energy systems with very high shares of wind power and CHP, neither the historical nor the expected future price variations on the spot market alone can justify the investment in CAES systems. Other storage technology options are significantly more feasible. CAES may operate both on the spot market and the regulating power market, which indicates potential feasibility. However, such strategy is highly risky because of the small extent of the regulating power market and if CAES is to become feasible it will depend on incomes from auxiliary services. [Copyright &y& Elsevier]

Abstract: This paper provides an introduction to the special issue on Sustainable Energy and Transportation Systems. No single technology can solve the problem of ever increasing CO2 emissions from stationary and transportation energy usage. Various single technologies must be put together and coordinated with parallel activities in the energy power generation and transportation infrastructure sectors. This special issue focuses on the methodologies and practices applied to the analysis of such sustainable energy and transportation systems. The three first papers discuss the possible changes in the transportation sector, which will make possible the integration of renewable energy. The potentials of electric, hybrid cars and hydrogen fuel cell cars are shown. Based on such recommendations, the succeeding four papers show how such technologies can be integrated into the electricity supply in such a way that fluctuating renewable energy sources are better integrated and utilised in the overall energy system. [Copyright &y& Elsevier]

Abstract: In 2005, wind power supplied 19% of the 36TWh annual electricity demand in Denmark, while 50% was produced at combined heat-and-power plants (CHP). The installed wind-turbine capacity in Western Denmark exceeds the local demand at certain points in time. So far, excess production has been exported to neighbouring countries. However, plans to expand wind power both in Denmark and in its neighbouring countries could restrain the export option and create transmission congestion challenges. This results in a need to increase the flexibility of the local electricity-system. Compressed-Air Energy-Storage (CAES) has been proposed as a potential solution for levelling fluctuating wind-power production and maintaining a system balance. This paper analyses the energy-balance effects of adding CAES to the Western Danish energy-system. Results show that even with an unlimited CAES plant capacity, excess power production is not eliminated because of the high percentage of CHP production. The optimal wind-power penetration for maximum CAES operation is found to be around 55%. The minimum storage size for CAES to fully eliminate condensing power plants operation in the optimized system is over 500GWh, which corresponds to a cavern volume of around 234Mm3 at an average pressure of 60 bar. Such a storage size would be technically and economically unfeasible. The analysis, however, did not include the potential role of a CAES plant in regulating the power services. [Copyright &y& Elsevier]

Abstract: This paper presents a comparative study of two energy system analysis models both designed for the purpose of analysing electricity systems with a substantial share of fluctuating renewable energy. The first model (EnergyPLAN) has been designed for national and regional analyses. It has been used in the design of strategies for integration of wind power and other fluctuating renewable energy sources into the future energy supply. The model has been used for investigating new operation strategies and investments in flexibility in order to utilize wind power and avoid excess production. The other model (H2RES) has been designed for simulating the integration of renewable sources and hydrogen into island energy systems. The H2RES model can use wind, solar and hydro as renewable energy sources and diesel blocks as backup. The latest version of the H2RES model has an integrated grid connection with the mainland. The H2RES model was tested on the power system of Porto Santo Island, Madeira, Portugal, Corvo and Graciosa Islands, Azores Islands, Portugal and Sal Island, Cape Verde. This paper presents the results of using the two different models on the same case, the island of Mljet, Croatia. The paper compares methodologies and results with the purpose of identifying mutual benefits and improvements of both models. [Copyright &y& Elsevier]

Abstract: This paper discusses the perspective of renewable energy (wind, solar, wave and biomass) in the making of strategies for a sustainable development. Such strategies typically involve three major technological changes: energy savings on the demand side, efficiency improvements in the energy production, and replacement of fossil fuels by various sources of renewable energy. Consequently, large-scale renewable energy implementation plans must include strategies for integrating renewable sources in coherent energy systems influenced by energy savings and efficiency measures. Based on the case of Denmark, this paper discusses the problems and perspectives of converting present energy systems into a 100% renewable energy system. The conclusion is that such development is possible. The necessary renewable energy sources are present, and if further technological improvements of the energy system are achieved the renewable energy system can be created. Especially technologies of converting the transportation sector and the introduction of flexible energy system technologies are crucial. [Copyright &y& Elsevier]

Abstract: Combined heat and power (CHP) as well as intermittent renewable energy sources (RES) are key elements in future cleaner electricity production systems. This article presents solutions which will integrate fluctuating renewable electricity supplies, such as wind power, into electricity systems using small and medium-sized combined heat and power plants (CHP). Such solutions call for a new organisational setup of partnerships and software tools. The software tools will allow the new partnerships to offer services which are currently only offered by big power plants to electricity markets. The article presents recent results of the development and implementation of such partnerships and focuses on the methodologies and computer tools necessary in order to allow the partnerships to optimise their behaviour on the market. The use of such tools and methodologies makes groups of small CHP plants able to replace large power stations and, at the same time, allows for the integration of a higher share of RES in the electricity supply, resulting in a decrease in both fossil fuels and CO2 emissions. [Copyright &y& Elsevier]

Abstract: The paper presents the ability of different energy systems and regulation strategies to integrate wind power. The ability is expressed by the following three factors: the degree of electricity excess production caused by fluctuations in wind and Combined Heat and Power (CHP) heat demands, the ability to utilise wind power to reduce CO2 emission in the system, and the ability to benefit from exchange of electricity on the market. Energy systems and regulation strategies are analysed in the range of a wind power input from 0 to 100% of the electricity demand. Based on the Danish energy system, in which 50% of the electricity demand is produced in CHP, a number of future energy systems with CO2 reduction potentials are analysed, i.e. systems with more CHP, systems using electricity for transportation (battery or hydrogen vehicles) and systems with fuel-cell technologies. For the present and such potential future energy systems different regulation strategies have been analysed, i.e. the inclusion of small CHP plants into the regulation task of electricity balancing and ancillary grid stability services and investments in electric heating, heat pumps and heat storage capacity. The results of the analyses make it possible to compare short-term and long-term potentials of different strategies of large-scale integration of wind power. [Copyright &y& Elsevier]

This article presents a methodology of showing the rate of integration of specific renewable energy sources (RESs) into the electricity supply system. The methodology is used on large-scale integration of wind, photo voltaic and wave power into a future Danish reference energy system. The possibility of integrating RES into the electricity supply is expressed in terms of the ability to avoid excess electricity production. The different sources are analysed in the range of an electricity production from 0 to 100% of the electricity demand. The excess production is found from detailed energy system analyses on the computer model EnergyPLAN. The analyses have taken into account that certain ancillary services are needed in order to secure the electricity supply system. The conclusion is that different patterns of each of the RES can be shown in terms of excess electricity diagrams. Such diagrams do not differ from one year to another, but do differ from one RES to another. [ABSTRACT FROM AUTHOR]

Renewable energy has been prioritized in Danish energy policy since the early 1980s. This has led to the current situation where Denmark is one of the leading countries in the world in the field of wind energy utilization. The background for this success is a story about how a society can manage the development and diffusion of sustainable technologies so that they are simultaneously socially acceptable and environmentally benign. Consequently, this article describes the relationship between the organization of wind power and the protection of nature. The aim is to analyse which kinds of public planning and policy can promote wind power and nature protection in a situation where a conflict exists between these two issues. The discussion acknowledges that it has been a serious problem to balance these contrasting considerations. However, it also suggests that the problems seem solvable if technology development, the social organization relating to the use of the technology and proper planning are brought together to work in a spirit of local involvement. © 1998 John Wiley & Sons, Ltd. and ERP Environment [ABSTRACT FROM AUTHOR]

This short paper gives some perspectives on the recent development in the concept of Smart Energy Systems while introducing the contents of selected papers from the 5th International Conference on Smart Energy Systems, 4th Generation District Heating, Electrification, Electrofuels and Energy Efficiency – SESAAU2019. All of the papers elaborate on or contribute to the theoretical scientific understanding on how to design and implement an energy efficient green transition with an emphasis on system integration and sector-coupling. Low-temperature 4th generation district heating and its possibilities of providing flexible demand is particularly emphasized in the papers presented. However, in order to reach 100% renewability in the energy system, further research is required particularly on the transformation of the transport and industrial sectors. Methods for accommodating increased levels of renewable energy sources, while maintaining proper load-balancing capability and security of supply, should also be further investigated – an area where smart energy systems play an important role. • Recent studies related to the development of Smart Energy Systems are presented. • Studies are divided in 6 categories, each contributing to the green transition. • The overall development is discussed, and perspectives on this research is presented. [ABSTRACT FROM AUTHOR]

Recent studies show that a high share of district heating is an important part of a future sustainable energy system or smart energy system with a high renewable energy penetration. These studies also show socio-economic benefits of expanding the district heating coverage. However, in order to implement such an expansion, district heating needs to be economically feasible for the heat consumers. This aspect is often not investigated and hence it is unknown if calculations based on consumer-economy, where tax payment is included, will yield the same potential of expansion. This study identifies the differences in the expansion potential of district heating calculated with a socio-economic and a consumer-economic approach, respectively, in a case study of Denmark. By also investigating the consumer-economy of expanding district heating, a deeper insight is obtained of possible locations for expanding district heating under the current framework conditions. [ABSTRACT FROM AUTHOR]

Reducing energy-related greenhouse gas emissions in the energy, buildings, industry and transport sectors plays a key role in combating climate change. This energy transition requires interdisciplinary work in the areas of sustainable development of energy, water and environment systems, including technical, economic, ecological and social assessments. Since 2002, the Conferences on Sustainable Development of Energy, Water and Environmental Systems (SDEWES) have provided a growing international scientific forum for the presentation and discussion of new research findings and solutions to these challenges. This editorial provides an overview of some of the latest work presented at SDEWES 2023. The papers published in this special issue highlight new findings in the fields of renewable energy systems and energy system modelling, as well as research into transitions in the space heating, mobility and industrial sectors. The overview clearly shows that, in addition to the development of individual technologies, their interaction, including flexibility options and sector coupling, is crucial for a successful energy transition. The review emphasizes that integrated renewable energy systems are a key factor for a more sustainable development of energy, water and environmental systems. In this context, overall system efficiency will become more important as a new performance indicator than the pure energy efficiency of individual conversion steps. [ABSTRACT FROM AUTHOR]

Abstract: Renewable energy is one of the possible solutions when addressing climate change. Today, large-scale renewable energy integration needs to include the experience to balance the discrepancy between electricity demand and supply. The electrification of transportation may have the potential to deal with this imbalance and to reduce its high dependence on oil production. For this reason, it is interesting to analyse the extent to which transport electrification can further the renewable energy integration. This paper quantifies this issue in Inner Mongolia, where the share of wind power in the electricity supply was 6.5% in 2009 and which has the plan to develop large-scale wind power. The results show that electric vehicles (EVs) have the ability to balance the electricity demand and supply and to further the wind power integration. In the best case, the energy system with EV can increase wind power integration by 8%. The application of EVs benefits from saving both energy system cost and fuel cost. However, the negative consequences of decreasing energy system efficiency and increasing the CO2 emission should be noted when applying the hydrogen fuel cell vehicle (HFCV). The results also indicate that developing renewable energy is crucial for transportation electrification. [Copyright &y& Elsevier]

Decarbonising the heating sector is one of the key elements to realizing the ambitious dual carbon goals of China, which is the largest carbon emitter and energy consumer globally. Currently, district heating (DH) systems have penetrated approximately 88% of the urban heating areas in Northern China. Nevertheless, around 90% of the heating demand in China still relies on fossil fuels. A larger scale integration of renewable energy and waste heat sources into the DH systems is critical for decarbonising the entire heating sector in China. However, a deeper level of comprehension is required to harness its full potential. This paper provides a thorough investigation of the status, potential, and national policy schemes of renewable energy and waste heat recovery in the DH systems of China. Combined with a critical review of recent literature on relevant areas published in both international and Chinese domestic sources, the trends, challenges, and future perspectives are discussed from scientific research and practical implementation aspects. This paper highlights the synergy of the integration of renewable energy and waste heat sources in DH, the energy efficiency improvements as well as the use of thermal storage technologies through the implementation of 4th generation district heating and smart energy systems that could offer a more economically viable pathway forward. • Focus on renewable energy and waste heat (REWH) in the district heating (DH) systems in China. • A systematic review of REWH in Chinese DH systems from status, policy, and literature aspects. • Identification of research gaps based on the review of both international and Chinese journals. • Policy recommendations proposed to promote REWH in Chinese DH systems. • The introduction of international experiences on REWH in DH for analysis in the Chinese context. [ABSTRACT FROM AUTHOR]

Integration of different energy infrastructures (heat, electricity and gas vectors) offers great potential for better managing energy sources, reducing consumption and waste as well as enabling a higher share of renewables, lower environmental impact and lower costs. This paper aims at reviewing the state-of-the-art energy system infrastructures in order to provide a comprehensive overview of technologies, operational strategies, modelling aspects and the trends towards integration of heat, electricity and gas infrastructures. Various technological domains are taken into account, ranging from energy distribution networks (thermal, electric and gas), components for the energy vector conversion (e.g. combined heat and power, power to heat, power to gas, etc.) and energy storage. Furthermore, the aspects related to smart management in energy systems are investigated, such as integration of renewable energy sources and energy recovery systems. • A review of separated and integrated energy infrastructures (EI) is here presented. • The main components in EI are networks, energy vector conversion systems and storages. • Electricity, thermal and gas facilities are increasingly interconnected. • Transition towards multi-energy systems is changing conception of EI. • Trends, technology and modelling aspects are here investigated. [ABSTRACT FROM AUTHOR]

The environmental impact of the energy sector and the security and economics of energy supply and utilisation have been raising increasing concerns, stimulating the search for innovative solutions for a sustainable use of resources. This article provides an overview of published research in this area, with a focus on papers contributed in special issues of leading journals dedicated to the series of Conferences on Sustainable Development of Energy, Water and Environment Systems (SDEWES), including the articles in the current special issue. Based on this review, research trends are identified and achievements supporting the energy transition are highlighted. The studies that focused on regional or urban energy planning have aimed at (a) increasing penetration of renewable energy sources, (b) optimizing the mix of centralized and distributed technologies (c) introducing additional flexibility in the power sector and (d) identifying solutions for sustainable heating. Conversely, researches focused on single plants or users have targeted the development of technologies for efficient energy use in industry and buildings, with emphasis on multi-generation and waste heat utilisation. The review highlights that future scenarios based on sustainable energy systems are viable, although their implementation will require further efforts by researchers and investors and active involvement of consumers. • Research trends on energy transition and the associated technologies are reviewed. • Literature review examined the Special Issues of journals dedicated to SDEWES Conferences. • Challenges posed by increased share of renewables are solvable by cost-efficient solutions. • Power-to-heat and district heating are key-technologies for sustainable energy supply. • Energy saving in the building and industrial sectors contributes to sustainability of energy sector. [ABSTRACT FROM AUTHOR]

The aim of this paper is to present options to make low-carbon footprint large-scale desalination a reality on arid islands with weak electrical grids. Through these options, the goal is to reconfigure on-grid wind energy/desalination systems for large- and medium-scale water production. In this context, it is proposed to use lithium-ion batteries for stationary energy storage together with management strategies aimed at avoiding the wind energy/desalination systems having to consume energy from the conventional grid they are connected to. The control strategy is based on ensuring that the power provided by the wind farm and batteries remains in synchrony with the power demand of the desalination plant throughout the system's useful life. The interannual variation of wind energy is considered when sizing the renewable energy system and processes for its estimation are proposed. The case study is centred on the Canary Archipelago, a region that is especially vulnerable to the impacts of climate change, but which enjoys exceptional characteristics for the exploitation of wind energy. The results obtained show the optimal wind farm and energy storage system capacities of the analysed configurations. The approach presented allows a low-carbon operational footprint. If the control strategy were to be put into practice today, the current grid restrictions and a life cycle assessment of the system carried out in a societal context that continues to be fossil fuel dependent indicate a potential reduction of 77.4% of the footprint. However, the remaining 22.6% could be eliminated in the future when the manufacturing processes of wind turbines, batteries and desalination plants receive the benefits of carbon-neutral societies. [Display omitted] • A method for achieving large-scale, low-carbon desalination is presented. • Optimal wind farm and storage capacities for the system are determined. • The method offers substantial CO2 emission reduction potential. • Using climate ERA5 reanalysis data, enhances robustness by addressing wind variability. • Proposed adjustments enhance adaptability to technological advances and future scenarios. [ABSTRACT FROM AUTHOR]

[Display omitted] • Optimal energy planning scenarios are obtained to boost the EV on islands. • Validation of scenarios with a higher participation of EVs on islands is conducted. • RES participation increases with EVs on islands, making generation costs lower. • Optimal EnergyPLAN scenario meets TSO grid criteria. This article discusses the integration of renewable energy sources in islanded energy systems, focusing on electrification of the transport sector and highlighting the challenges that are faced. The proposed method comprises different steps. First, the energy system is analyzed using the Smart Energy Systems concept to identify high renewable energy scenarios. Then, the power system is evaluated to ensure compliance with security and stability requirements. The method innovatively combines an overall energy system analysis, from an energy planning perspective, with more detailed power system analyses, where the power balance at each instant is the main item of interest rather than the energy balance. The study, applied to Gran Canaria (Canary Islands, Spain), demonstrates that 100% electrification of passenger cars with renewable energy sources is the optimal scenario, resulting in reductions of 45.86% and 45.1% in oil consumption and CO 2 emissions, respectively, compared to the reference scenario. In addition, in these optimal conditions, there would be a 29.9% reduction in the total annual costs of the energy system and a 13.81% reduction in the total energy required to supply it. The stability analysis that was undertaken confirms that the system can handle a significant electric vehicle load and high renewable energy production without excessive load shedding. [ABSTRACT FROM AUTHOR]

Climate change and fossil fuel reserve depletion both pose challenges for energy security and for wellbeing in general. The top ten among them include: Decarbonising the world economy; Enhancing the energy efficiency and energy savings in buildings; Advancing the energy technologies; Moving towards energy systems based on variable renewables; Electrifying the transport and some industrial processes; Liberalizing and extending the energy markets; Integrating energy sectors to Smart Energy Systems; Making the cities and communities smart; Diversifying the energy sources; and Building more biorefineries. Presenting the contributions of selected conference papers published in the special issues of leading scientific journals (including all the papers from the current Energy special issue), this review demonstrates the capacity of the Conferences on Sustainable Development of Energy, Water and Environment Systems for generation of knowledge which could serve as the centrepiece of a pertinent response to those challenges. [ABSTRACT FROM AUTHOR]