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This article presents some of the main findings from the SDEWES conferences of 2021 within the field of renewable energy. More specifically, results are summarized and contextualised within solar energy and thermal comfort, wind power resource assessment, and biogas and biomass resources and technology. The two last sections deal more broadly with energy systems and energy systems transition issues; the systems analyses used to design complex renewable energy systems and the investment strategies and barriers associated with the transition. This article presents some of the main findings from the SDEWES conferences of 2021 within the field of renewable energy. More specifically, results are summarized and contextualised within solar energy and thermal comfort, wind power resource assessment, and biogas and biomass resources and technology. The two last sections deal more broadly with energy systems and energy systems transition issues; the systems analyses used to design complex renewable energy systems and the investment strategies and barriers associated with the transition.

This paper presents the first comprehensive hourly-resolution scenario study of the Indian electricity system with a view to investigate the transition from fossil to renewable energy-based power generation. Currently, India is 76% dependent on coal for power generation, however ambitious goals exist. Energy organisations including International Renewable Energy Agency and The Energy and Resources Institute, have presented scenarios but neither with support of dynamic simulation nor with assessment of optimal renewable energy contributions. In this paper, the optimal electricity system is analyzed in comparison with these. Results show that an optimal scenario could supply the hourly electricity by (i) increasing production capacity to about 615 GW, which is a 98.3% increase compared to the 310 GW in 2016, (ii) improving capacity factor of wind power and photovoltaic to 27% and 21% respectively, (iii) increasing wind power production to 433 TWh/yr (from 46 GWh/yr in 2016), solar photovoltaic to 290 TWh/yr (12 GWh/yr in 2016), river hydro to 42 TWh/yr (7.7 GWh/yr in 2016), biomass and nuclear power of 15 GW each. The costs of the identified optimal scenario are lower than of the previous scenarios. Finally, simulations show that inclusion of optimal proportion of biomass and nuclear could avoid any import dependency.

Island energy systems should aim for a better integration of local resources and exploit their potential for local energy supply to increase their independence and security of supply besides other benefits. Two trends addressing this problem can be observed: On the one hand, increasing the local use of renewable electricity in the electricity sector by investing in Battery Energy Storage Systems (BESS). On the other hand, the integration of all energy sectors into a Smart Energy System (SES) with the conversion of renewable electricity to heat – thus enabling the usage of Thermal Energy Storage (TES). In this paper, these two potential approaches are investigated through energy systems analyses using EnergyPLAN for the Danish island Samso and the Orkney islands in Scotland. This investigation shows that BESS tend to address only the electricity sector, while TES furthermore improves issues in the heating sector and enables possibilities in the transport sector. The TES approach results in overall reduced energy system costs, while the BESS has a stronger effect on the exchange of electricity. Depending on the various energy systems, both approaches present potential solutions, while the SES approach with the use of TES demonstrates more advantages for the whole energy system.

Hydropower has the advantages of quickly responding to load variability, which overcomes the unpredictable and unstable variabilities of solar and wind power. Therefore, such power generation can be combined into a hydro-wind-photovoltaic complementary plant (HWPCP). However, hydropower units running at partial load are prone to suffer from hydraulic instabilities generated by a cavitating vortex rope, which may lead to power swings and high vibrations. Operation in these vibration zones may affect the operation and ultimately cause structural damage and affect the power plant. The problem of avoiding running hydropower units in the vibration zones is effectively addressed in this study. This is achieved by adopting a vibration avoidance strategy to determine a rational power distribution scheme for hydropower units. Multi-objective optimization is performed to maximize power generation, minimize output power fluctuations, and minimize the deviation between the power generation and the planned output. The power distribution strategies of hydropower units under 12 scenarios, composed of different inflow and weather conditions, are analyzed. The results indicate that the vibration avoidance strategy effectively avoids the operation of hydropower units in the vibration zones and ensures the operation of hydropower units in the non-vibration zone for more than 99.31% of the operation time. This study contributes to the identification of the relationship between conflicting objectives and provides operational strategies for the safe and stable operation of hydropower units. Hydropower has the advantages of quickly responding to load variability, which overcomes the unpredictable and unstable variabilities of solar and wind power. Therefore, such power generation can be combined into a hydro-wind-photovoltaic complementary plant (HWPCP). However, hydropower units running at partial load are prone to suffer from hydraulic instabilities generated by a cavitating vortex rope, which may lead to power swings and high vibrations. Operation in these vibration zones may affect the operation and ultimately cause structural damage and affect the power plant. The problem of avoiding running hydropower units in the vibration zones is effectively addressed in this study. This is achieved by adopting a vibration avoidance strategy to determine a rational power distribution scheme for hydropower units. Multi-objective optimization is performed to maximize power generation, minimize output power fluctuations, and minimize the deviation between the power generation and the planned output. The power distribution strategies of hydropower units under 12 scenarios, composed of different inflow and weather conditions, are analyzed. The results indicate that the vibration avoidance strategy effectively avoids the operation of hydropower units in the vibration zones and ensures the operation of hydropower units in the non-vibration zone for more than 99.31% of the operation time. This study contributes to the identification of the relationship between conflicting objectives and provides operational strategies for the safe and stable operation of hydropower units.

EnergyPLAN is an energy system analysis tool created for the study and research in the design of future sustainable energy solutions with a special focus on energy systems with high shares of renewable energy sources. The tool has been under development since 1999 and has formed the basis for a substantial number of PhD theses and several hundreds of research papers. EnergyPLAN is designed to exploit the synergies enabled from including the whole energy system, as expressed in the smart energy system concept. Thus, with EnergyPLAN, the user can take a holistic approach focusing on the analysis of the cross-sectoral interaction. Traditionally disparate demand sectors, such as buildings, industry and transport, are linked with supply technologies through electricity, gas, district heating and cooling grids. In this way, EnergyPLAN enables the analysis of the conversion of renewable electricity into other energy carriers, such as heat, hydrogen, green gases and electrofuels, as well as the implementation of energy efficiency improvements and energy conservation. This article describes the overall structure of EnergyPLAN and the essential algorithms and computational structure. EnergyPLAN is an energy system analysis tool created for the study and research in the design of future sustainable energy solutions with a special focus on energy systems with high shares of renewable energy sources. It has been under development since 1999 and has formed the basis for a substantial number of PhD theses and several hundreds of research papers. EnergyPLAN is designed to exploit the synergies enabled from including the whole energy system, as expressed in the smart energy system concept. Thus, with EnergyPLAN, the user can take a holistic approach focusing on the analysis of the cross-sectoral interaction. Traditionally disparate demand sectors, such as buildings, industry and transport, are linked with supply technologies through electricity, gas, district heating and cooling grids. In this way, EnergyPLAN enables the analysis of the conversion of renewable electricity into other energy carriers, such as heat, hydrogen, green gases and electrofuels, as well as the implementation of energy efficiency improvements and energy conservation. This article describes the overall structure of EnergyPLAN and the essential algorithms and computational structure.

District heating is a well-established system for providing energy efficient space and domestic hot water heating in dwellings in particularly in temperate and cold climate zones. Research has shown that going from the current 3rd generation district heating (3GDH) systems towards 4th generation district heating (4GDH) systems can facilitate a better integration between energy sectors, reduce grid losses and assist the integration of renewable energy sources. This article investigates the economic and energy effects of going from 3GDH to 4GDH for the specific case of Aalborg Municipality, Denmark based on overall hourly energy systems simulations. The analyses include effects from changes in excess heat potentials, changes in grid losses, and changes in efficiencies of conversion units in the district heating. Altogether, the analyses of the Aalborg case reveal that going from 3GDH to 4GDH decreases the primary energy consumption of the entire energy system by around 4.5% and the costs of the system by 2.7%.

The global COVID-19 pandemic has had strong impacts on national and international freight, construction and tourism industry, supply chains, and has resulted in a rapid decline in the demand for traditional energy sources. In fact, research has outlined that urban areas depend on global supply chains for their day-to-day basic functions, including energy supplies, food and safe access to potable water. The disruption of global supply chains can leave many urban areas in a very vulnerable position, in which their citizens may struggle to obtain their basic supplies, as the COVID-19 crisis has recently shown. Therefore, solutions aiming to enhance local food, water and energy production systems, even in urban environments, have to be pursued. The COVID-19 crisis has also highlighted in the scientific community the problem of people’s exposure to outdoor and indoor pollution, confirmed as a key element for the increase both in the transmission and severity of the contagion, on top of involving health risks on their own. In this context, most nations are going to adopt new preferential policies to stimulate the development of relevant sustainable energy industries, based on the electrification of the systems supplied by renewable energy sources as confirmed by the International Energy Agency (IEA). Thus, while there is ongoing research focusing on a COVID 19 vaccine, there is also a need for researchers to work cooperatively on novel strategies for world economic recovery incorporating renewable energy policy, technology and management. In this framework, the Sustainable Development of Energy, Water and Environment Systems (SDEWES) conference provides a good platform for researchers and other experts to exchange their academic thoughts, promoting the development and improvements on the renewable energy technologies as well as their role in systems and in the transition towards sustainable energy systems. The 14th SDEWES Conference was held in Dubrovnik, Croatia. It brought together around 570 researchers from 55 countries in the field of sustainable development. The present Special Issue of Energies, specifically dedicated to the 14th SDEWES Conference, focuses on four main fields: energy policy for sustainable development, biomass energy application, building energy saving, and power plant and electric systems. The global COVID-19 pandemic has had strong impacts on national and international freight, construction and tourism industry, supply chains, and has resulted in a rapid decline in the demand for traditional energy sources. In fact, research has outlined that urban areas depend on global supply chains for their day-to-day basic functions, including energy supplies, food and safe access to potable water. The disruption of global supply chains can leave many urban areas in a very vulnerable position, in which their citizens may struggle to obtain their basic supplies, as the COVID-19 crisis has recently shown. Therefore, solutions aiming to enhance local food, water and energy production systems, even in urban environments, have to be pursued. The COVID-19 crisis has also highlighted in the scientific community the problem of people’s exposure to outdoor and indoor pollution, confirmed as a key element for the increase both in the transmission and severity of the contagion, on top of involving health risks on their own. In this context, most nations are going to adopt new preferential policies to stimulate the development of relevant sustainable energy industries, based on the electrification of the systems supplied by renewable energy sources as confirmed by the International Energy Agency (IEA). Thus, while there is ongoing research focusing on a COVID 19 vaccine, there is also a need for researchers to work cooperatively on novel strategies for world economic recovery incorporating renewable energy policy, technology and management. In this framework, the Sustainable Development of Energy, Water and Environment Systems (SDEWES) conference provides a good platform for researchers and other experts to exchange their academic thoughts, promoting the development and improvements on the renewable energy technologies as well as their role in systems and in the transition towards sustainable energy systems. The 14th SDEWES Conference was held in Dubrovnik, Croatia. It brought together around 570 researchers from 55 countries in the field of sustainable development. The present Special Issue of Energies, specifically dedicated to the 14th SDEWES Conference, focuses on four main fields: energy policy for sustainable development, biomass energy application, building energy saving, and power plant and electric systems.

The transition towards renewable energy will operate on different geographical scales. Many of the concrete steps will address the local level; however, these have to align with the broader energy perspective. It is therefore necessary to develop methods that enable cities to assess the compatibility of the local renewable energy strategy to the surrounding national and global energy systems. This paper presents a methodology to design Smart Energy Cities within the context of 100% renewable energy at a national level. Cities and municipalities should act locally with regard to local demands but acknowledge the national and global context when addressing resources, industry and transport. The method is applied to the case of transitioning the municipality of Aalborg to a 100% renewable smart energy system within the context of a Danish and European energy system. The case demonstrates how it is possible to transition to a Smart Energy City that fits within a 100% renewable energy context of Denmark and Europe. The suggested methodology is framed in a way that makes it applicable to other cases globally.

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.

District heating systems are appropriate infrastructures to supply space heating and domestic hot water from a number of potential sources in future energy systems based on renewable energy. On the other hand, district heating is also facing competition from heating technologies in individual buildings. Lowering the district heating temperatures will improve efficiency and competitiveness of district heating; however, the production of domestic hot water is an impediment to this. This article uses energyPRO to analyse three low-temperature district heating schemes. District heating is supplied from a heat pump using air, seawater or groundwater as heat sources. Domestic hot water is supplied by booster heat pumps using district heating as heat source or through a heat exchanger. The economic benefit of adding booster heat pumps to cover the domestic hot water demands is assessed by modelling the time-varying operation against the electricity market as well as the time-varying coefficient of performance of heat pumps and grid losses. Based on this operation cost reduction assessment, the energy system value of booster heat pumps ranges from 2500 to 6800€ per house depending on the choice of low-temperature heat source for the district heating heat pump as well as economic time-horizon and discount rate.

This paper addresses economic aspects of heat savings in the context of strategic heat planning. The analysis uses the city of Aalborg, Denmark, as a case where municipalisation through a recent acquisition of a coal-fired cogeneration of heat and power (CHP) plant has made an update of a municipal strategic energy plan necessary. Combining datasets on buildings and insulation techniques with economic methods, we investigate how the local district heating tariff can be adapted to improve the conditions for heat savings and support the transition to lower supply temperatures in line with the requirements of future fourth generation district heating systems. The paper concludes that implementing a fully variable heat tariff scheme improves the financial incentive for heat savings, while also making the system development less vulnerable to fluctuations and shortages in capital markets. The paper supplements existing literature on heat savings with novelty in its approach and in its systematic investigation of the interplay between tariff policies and interest rates. This paper addresses economic aspects of heat savings in the context of strategic heat planning. The analysis uses the city of Aalborg, Denmark, as a case where municipalisation through a recent acquisition of a coal-fired cogeneration of heat and power (CHP) plant has made an update of a municipal strategic energy plan necessary. Combining datasets on buildings and insulation techniques with economic methods, we investigate how the local district heating tariff can be adapted to improve the conditions for heat savings and support the transition to lower supply temperatures in line with the requirements of future fourth generation district heating systems. The paper concludes that implementing a fully variable heat tariff scheme improves the financial incentive for heat savings, while also making the system development less vulnerable to fluctuations and shortages in capital markets. The paper supplements existing literature on heat savings with novelty in its approach and in its systematic investigation of the interplay between tariff policies and interest rates.

Mini-grids have been widely developed for rural electrification purposes in Kenya, predominantly as systems combining photovoltaic modules (PV), a diesel generator, and battery capacity. (Small) wind turbines have been largely neglected in such setups and are basically non-existent in Kenyan mini-grids despite potential complementarity with PV due to different temporal production profiles of PV and wind power.This study investigates why small wind turbines have largely been omitted from Kenyan mini-grids from both a techno-economic and diffusion theoretical perspective. A techno-economic model is used for backtesting the feasibility of a hybrid PV/wind system, and building upon theories of innovation and diffusion of technology a conceptual framework is developed and applied for assessing the state of the Kenyan mini-grid sector and categorizing identified barriers accordingly.The article thus suggest an interdisciplinary approach to investigating the potential role of small wind power in energy systems transitioning towards renewables.The techno-economic modelling shows that PV/wind hybrids have both technical and economic potential at average wind speeds above 4.5 m/s but little relevance below. Comprehensive barriers within the technical, economic and systemic spheres are encountered by established stakeholders of the Kenyan mini-grid sector, severely hindering diffusion of hybrid PV/wind solutions. Mini-grids have been widely developed for rural electrification purposes in Kenya, predominantly as systems combining photovoltaic modules (PV), a diesel generator, and battery capacity. (Small) wind turbines have been largely neglected in such setups and are basically non-existent in Kenyan mini-grids despite potential complementarity with PV due to different temporal production profiles of PV and wind power.This study investigates why small wind turbines have largely been omitted from Kenyan mini-grids from both a techno-economic and diffusion theoretical perspective. A techno-economic model is used for backtesting the feasibility of a hybrid PV/wind system, and building upon theories of innovation and diffusion of technology a conceptual framework is developed and applied for assessing the state of the Kenyan mini-grid sector and categorizing identified barriers accordingly.The article thus suggest an interdisciplinary approach to investigating the potential role of small wind power in energy systems transitioning towards renewables.The techno-economic modelling shows that PV/wind hybrids have both technical and economic potential at average wind speeds above 4.5 m/s but little relevance below. Comprehensive barriers within the technical, economic and systemic spheres are encountered by established stakeholders of the Kenyan mini-grid sector, severely hindering diffusion of hybrid PV/wind solutions.

This article present a review of the status of research within the exploitation of renewable energy sources with a focus on the status of technologies exploiting renewable energy sources, a status of the assessment of the availability of renewable energy sources and the status on the research into the types of systems, that can integrate renewable energy sources. In terms of technologies and resources, wind and wave power resources, wind technology, geothermal energy, solar heating, cooling and electricity and salinity gradient technologies are reviewed. Lastly, system integration, impacts and environmental performance of energy systems are assessed. The review takes a starting point in work presented at the conference series on Sustainable Development of Energy, Water and Environmental Systems (SDEWES), published in Special Issues in various journals and puts this work into a wider context. This article present a review of the status of research within the exploitation of renewable energy sources with a focus on the status of technologies exploiting renewable energy sources, a status of the assessment of the availability of renewable energy sources and the status on the research into the types of systems, that can integrate renewable energy sources. In terms of technologies and resources, wind and wave power resources, wind technology, geothermal energy, solar heating, cooling and electricity and salinity gradient technologies are reviewed. Lastly, system integration, impacts and environmental performance of energy systems are assessed. The review takes a starting point in work presented at the conference series on Sustainable Development of Energy, Water and Environmental Systems (SDEWES), published in Special Issues in various journals and puts this work into a wider context.

Currently, Kenya depends mainly on oil, geothermal energy and hydro resources for electricity production, however all three have associated issues. Oil-based electricity generation is environmentally harmful, expensive and a burden to the national trade balance. The rivers for hydropower and their tributaries are found in arid and semi-arid areas with erratic rainfall leading to problems of supply security, and geothermal exploitation has cost and risk issues amongst others. Given these problems and the fact that Kenya has a significant yet underexploited potential for photo voltaic (PV)-based power generation, the limited—although growing—exploitation of solar PV in Kenya is explored in this paper as a means of diversifying and stabilising electricity supply. The potential for integration of PV into the Kenyan electricity generation mix is analysed together with the sociotechnical, economic, political, and institutional and policy barriers, which limit PV integration. We argue that these barriers can be overcome with improved and more robust policy regulations, additional investments in research and development, and improved coordination of the use of different renewable energy sources. Most noticeably, storage solutions and other elements of flexibility need to be incorporated to balance the intermittent character of electricity generation based on solar PV. Currently, Kenya depends mainly on oil, geothermal energy and hydro resources for electricity production, however all three have associated issues. Oil-based electricity generation is environmentally harmful, expensive and a burden to the national trade balance. The rivers for hydropower and their tributaries are found in arid and semi-arid areas with erratic rainfall leading to problems of supply security, and geothermal exploitation has cost and risk issues amongst others. Given these problems and the fact that Kenya has a significant yet underexploited potential for photo voltaic (PV)-based power generation, the limited—although growing—exploitation of solar PV in Kenya is explored in this paper as a means of diversifying and stabilising electricity supply. The potential for integration of PV into the Kenyan electricity generation mix is analysed together with the sociotechnical, economic, political, and institutional and policy barriers, which limit PV integration. We argue that these barriers can be overcome with improved and more robust policy regulations, additional investments in research and development, and improved coordination of the use of different renewable energy sources. Most noticeably, storage solutions and other elements of flexibility need to be incorporated to balance the intermittent character of electricity generation based on solar PV.

This short paper introduces the contents of selected papers from the 4th International Conference on Smart Energy Systems and 4th Generation District Heating – SES4DH. All of the papers elaborate on or contribute to the theoretical scientific understanding on how we can design and implement a suitable and least-cost transformation into a sustainable energy future with a focus on the important role of district heating and cooling technologies. This short paper introduces the contents of selected papers from the 4th International Conference on Smart Energy Systems and 4th Generation District Heating – SES4DH. All of the papers elaborate on or contribute to the theoretical scientific understanding on how we can design and implement a suitable and least-cost transformation into a sustainable energy future with a focus on the important role of district heating and cooling technologies.

Combined heat and power units connected to district energy plants have an important role displacing condensing mode power generation and boiler-based heat-only generation. However, often the earnings on the electricity markets are not sufficient to promote the establishment of these; therefore, support schemes are needed. When designing a support scheme to promote combined heat and Power, it is important to consider that in the transition to a renewable energy system, the role changes radically from displacing traditional generation to assisting in the integration of fluctuating renewables and finally providing the electrical capacity needed during hours with insufficient wind and sun. An energyPRO-based comparison of a premium and a triple tariff support scheme is presented. The comparison shows that, during a 20-year period, the cost to society is less than half when using the triple tariff compared to using the premium scheme for providing a certain capacity. While this capacity displaces the same amount of production from condensing mode power plants, the triple tariff promotes larger thermal energy storage capacity compared to the premium scheme, which is beneficial for district energy combined heat and power to fulfil its subsequent tasks in a renewable energy system. Combined heat and power units connected to district energy plants have an important role displacing condensing mode power generation and boiler-based heat-only generation. However, often the earnings on the electricity markets are not sufficient to promote the establishment of these; therefore, support schemes are needed. When designing a support scheme to promote combined heat and Power, it is important to consider that in the transition to a renewable energy system, the role changes radically from displacing traditional generation to assisting in the integration of fluctuating renewables and finally providing the electrical capacity needed during hours with insufficient wind and sun. An energyPRO-based comparison of a premium and a triple tariff support scheme is presented. The comparison shows that, during a 20-year period, the cost to society is less than half when using the triple tariff compared to using the premium scheme for providing a certain capacity. While this capacity displaces the same amount of production from condensing mode power plants, the triple tariff promotes larger thermal energy storage capacity compared to the premium scheme, which is beneficial for district energy combined heat and power to fulfil its subsequent tasks in a renewable energy system.

Flexible District Energy plants providing heating and cooling to cities represent an important part of future smart renewable energy systems. Equipped with large combined heat and power units, heat pumps and thermal energy storage they have the possibility to provide flexibility – but an optimized unit commitment is required. A common conclusion has been that unit commitment based on analytic methods is not useful. However, the market-based operation of District Energy plants often being reduced to participation in one or two electricity markets, simplifies the unit commitment problem and brings analytic unit commitment methods back as potentially attractive methods for District Energy plants. This is demonstrated in this paper by establishing a complex generic District Energy plant which is yet so simplified that a solver-based Mixed Integer Linear Programming method is able to deliver optimal unit commitments. An advanced analytic unit commitment method for district energy plants is proposed and the comparison of the unit commitments made by this method with the optimal solver-based unit commitments shows that the method delivers operation income within 1% of the optimal operation income, which is fully adequate for daily operation planning, yearly budgeting and long-term investment analysis for this generic District Energy plant.

Heat pumps are foreseen to play a pivotal role in future renewable energy-based heating systems. In addition to supplying heat, they can assist the sector integration that facilitates the integration of fluctuating renewable energy-based electricity production. However, while heat pumps have this potential, they are also associated with high investment costs and modest operation costs. Thus, heat pumps give incentives for near-continuous operation and not the flexible operation required for renewable energy integration. This article investigates heat pumps from two perspectives: The impact of electricity taxes on a) the incentive to increase heat pump and thermal energy storage capacities to give the basis for flexible operation and b) the alignment of heat pump operation with the dynamic electricity system needs. Results show that a tax equal to the hourly spot market electricity price will provide the same fiscal income for the state as in the current system with a fixed tax and will provide incentives for tentatively 20% more thermal storage. However, the tax will not provide incentives for more heat pump capacity, but for a somewhat more flexible operation causing the heat pump/thermal energy storage combination to operate more according to electricity prices and less according to heat demands. Heat pumps are foreseen to play a pivotal role in future renewable energy-based heating systems. In addition to supplying heat, they can assist the sector integration that facilitates the integration of fluctuating renewable energy-based electricity production. However, while heat pumps have this potential, they are also associated with high investment costs and modest operation costs. Thus, heat pumps give incentives for near-continuous operation and not the flexible operation required for renewable energy integration. This article investigates heat pumps from two perspectives: The impact of electricity taxes on a) the incentive to increase heat pump and thermal energy storage capacities to give the basis for flexible operation and b) the alignment of heat pump operation with the dynamic electricity system needs. Results show that a tax equal to the hourly spot market electricity price will provide the same fiscal income for the state as in the current system with a fixed tax and will provide incentives for tentatively 20% more thermal storage. However, the tax will not provide incentives for more heat pump capacity, but for a somewhat more flexible operation causing the heat pump/thermal energy storage combination to operate more according to electricity prices and less according to heat demands.

District heating (DH) enables the utilisation and distribution of heating from sources unfeasible for stand-alone applications and combined with cogeneration of heat and power (CHP), has been the cornerstone of Denmark’s realisation of a steady national primary energy supply over the last four decades. However, progressively more energy-efficient houses and a steadily improving heat pump (HP) performance for individual dwellings is straining the competitive advantage of the CHP–DH combination as DH grid losses are growing in relative terms due to decreasing heating demands of buildings and relatively high DH supply temperatures. A main driver for the DH water temperature is the requirements for domestic hot water (DHW) production. This article investigates two alternatives for DHW supply: (a) DH based on central HPs combined with a heat exchanger, and (b) a combination of DH based on central HPs and a small booster HP using DH water as low-temperature source for DHW production. The analyses are conducted using the energyPRO simulation model and are conducted with hourly varying factors; heating demands, DH grid losses, HP coefficient of performance (COP) and spot market prices in order to be able to analyse the relative performance of the two options and their performance over the year. Results are also compared to individual boilers and individual HPs. The results indicate that applying booster HPs enables the DH system to operate at substantially lower temperature levels, improving the COP of central DH HPs while simultaneously lowering DH grid losses significantly. Thus, DH performance is increased significantly. Additionally, performance for the DH HP with booster combination is considerably better than individual boiler or HP solutions.

The need to act on the challenges brought by climate change calls for an increasing penetration of renewable energy sources (RES) in our society’s energy supply, but such integration can be challenging.This study analyzes the impact of large numbers of smart electric vehicles (EVs) in a real urban district, using the Italian town Osimo as a case study, to determine the achievable degree of RES self-consumption and CO2 emission reductions. Osimo features a multi-energy system with electricity, natural gas, district heating, and a 23% share of non-controllable RES capacity, mostly photovoltaics. The presence of EVs is evaluated in the present conditions and in scenarios with an increasing capacity of non-controllable RES. The case study is modeled in the deterministic hourly energy systems simulation model EnergyPLAN, which for these analyses is embedded within a framework aimed at enhancing its capabilities to consider the impact of uncertainties and obtain more robust results.The results show that a 10% EV penetration with vehicle-to-grid (V2G) capability can eliminate the need to export electricity surplus at the current PV capacity, lowering Osimo’s CO2 emissions by 3.5%. A 30% penetration achieves the same with twice the PV capacity, reducing the emissions of 17.6%.

Several countries have recently realized that the present development paradigm is notsustainable from an environmental and energy point of view. The growing awareness of thepopulation regarding environmental issues is pushing governments worldwide more and more topromote policies aiming at limiting harmful effects of human development. In particular, the rapidincrease of the global temperature, especially in the polar regions, and the management of humanwastes, mainly plastic in seas, are some of the main points to be addressed by these novel policies.Several actions must be implemented in order to limit such issues. Unfortunately, the recent COP24 Conference was not successful, but hopefully an agreement will be established in 2020 at theCOP 26 Conference. The effort performed by policymakers must be mandatorily supported by thescientific community. In this framework, this paper aims at showing that countries worldwide aretrying to negotiate an agreement to increase energy efficiency and reduce greenhouse gas (GHG)emissions. In addition, in this paper all the researchers reported can provide quantitative measures ofthe actions to be implemented in order to address a sustainable and efficient use of energy. Here,innovations in terms of novel efficient and environmentally friendly technologies mainly based onrenewable energy sources have been also investigated. The study also highlights different sectorsthat have been involved for this aim, such as energy conversion systems, urban areas, mobility,sustainability, water management, social aspects, etc. In this framework, specific conferences areperiodically organized in order to provide a forum for discussion regarding these topics. In this areathe Sustainable Development of Energy, Water and Environment Systems (SDEWES) conference isthe most ordinary conference. The 13th Sustainable Development of Energy, Water and EnvironmentSystems Conference was held in Palermo, Italy in 2018. The current Special Issue of Energies,precisely dedicated to the 13th SDEWES Conference, is based on three main topics: energy policy andenergy efficiency in urban areas, energy efficiency in industry and biomass and other miscellaneousenergy systems.

Flexible District Energy plants providing heating and cooling to cities have an important role in the transition to a renewable energy system. They may become major actors in integrating wind and solar power, when equipped with a combination of combined heat and power units, heat consuming absorption chillers, heat pumps producing both heating and cooling and large thermal energy stores. However, often electricity prices do not create sufficient feasibility for these to be installed thus calling for support schemes. The societal resources dedicated to support should be minimised while ensuring the establishment of an adequate amount and right ratio between these units. This paper presents a method for determining the capacities different support schemes will promote as a function of dedicated resources. The method is used in a comparison of two support schemes promoting combined heat and power; a premium on top of hourly wholesale electricity prices and a fixed Feed in Tariff. The comparison shows that the premium scheme requires a little less total support than the Feed In Tariff scheme for promoting a given amount of electrical capacity, but promotes a five-times larger thermal energy store capacity, thereby promoting substantially increased flexibility for integrating intermittent power production.

This article focuses on two components of local energy system planning. Firstly, a 100% local renewable energy system is created, based on the interplay between the electricity, heating and transport sectors. Secondly, an analysis of the integration of the proposed local system with the rest of the country is carried out, in order to see how the two systems influence each other. The EnergyPLAN model is used as the modelling tool for creating scenarios, while MultiNode, an add-on tool to EnergyPLAN, is used for the integration analysis. The proposed system is carbon neutral, has a 47% lower primary energy supply and has the same level of total annual costs as the existing system. The integration analysis shows that 14% of the excess electricity production can be utilized in the surrounding system, revealing an opportunity to increase the capacity of renewable technologies. Modelling the hourly integration between local and national system is proved to be more accurate and reliable in comparison to conventional integration studies with EnergyPLAN where only the interconnection capacity is defined. It is also the most efficient way to fully exploit the natural potentials and integrate high shares of renewables in a technically and economically feasible way.

Environmental and security concerns urge energy planners to design more sustainable energy systems, reducing fossil fuel consumptions in favour of renewable solutions. The proposed scenarios typically rely on a mixing of different energy sources, thereby mitigating the availability and intermittency problems typically related to renewable technologies. Optimizing this combination is of crucial importance to cope with economic, technical, and environmental issues, which typically give rise to multiple contradictory objectives. To this purpose, this article presents a generalized framework coupling EnergyPLAN – a descriptive analytical model for medium/large-scale energy systems – with a multi-objective evolutionary algorithm – a type of optimizer widely used in the context of complex problems. By using this framework, it is possible to automatically identify a set of Pareto-optimal configurations with respect to different competing objectives. As an example, the method is applied to the case of Aalborg municipality, Denmark, by choosing cost and carbon emission minimization as contrasting goals. Results are compared with a manually identified scenario, taken from previous literature. The automatic approach, while confirming that the available manual solution is very close to optimality, yields an entire set of additional optimal solutions, showing its effectiveness in the simultaneous analysis of a wide range of combinations.

The establishment of an optimal mix of renewable energy sources (RES) is pertinent to creating low-carbon energy systems with adequate load-following capabilities. Transitioning from a fossil fuel-based energy system to a system based on RES is a process in which the RES penetration must be guided by specific targets in the medium term. Moreover, the relative contributions from RES and fossil fuels in every stage of the transition process must be identified through clear optimization criteria. In this article, we propose a methodology denoted the Minimum Total Mix Capacity (MTMC) to determine the optimal mix of RES and fossil fuels in an electricity system by taking into account the hourly values of RES production and electricity demand. The MTMC methodology is applied to the Mexican electricity system, which greatly depends on fossil fuels. The Mexican Congress mandated that the fossil fuel-based electricity generation be limited to 65% by the year 2024, 60% by 2035 and 50% by 2050. We use the MTMC methodology to investigate the potential for RES integration into the Mexican electricity system by constructing three scenarios (low, mid and high biomass) to achieve the 2024 target and analyze the system’s response to varying contributions of wind and solar power production to the scenarios. The minimum complementary capacity based on fossil fuels that is needed to cover the demand without electricity imports is assessed to determine the total mix capacity for the transition system. Using the MTMC methodology, several combinations of biomass, wind and solar power that achieve a minimum of 35% RES electricity production are identified; however, there is only one combination that results in the minimum overall capacity, hence resulting in the optimal mix. Moreover, a domain of near-optimal mix combinations can be identified among all of the scenarios, which may also be considered as an alternative. Biomass has the highest effectiveness in terms of high RES production and the lowest required overall power generating capacity.

In this document a review of three active as well as ten passive cooling methods suitable for residential buildings is carried out. The review firstly addresses how the various technologies cool the space according to the terms of the building heat balance, under what technical conditions they might be applied, and what their energy needs are. Secondly, what scientific analysis has been carried out and what the major findings are. Thirdly, what their economic and technical feasibility of use at the stage of implementation and operation within a dwelling are. Then, either with the reviewed studies or with a simulation modelling, an assessment of temperature drop of each cooling method within a standard-size dwelling is carried out. Also, a comparison of initial investment, energy consumption, maintenance, retrofitting and required space is done. Thereafter, with this information, a decision-making program is developed in order to find out the most suitable cooling method of this dwelling in each case study according to the climate, status (new or existing), and the affordability. With that, and taking the Mexican housing sector as case study, it is found that building color, shading system, night ventilation, controlled ventilation, roof coating and eco-evaporative cooling are the most suitable passive methods for an extensive use in this country.

In 2006, a number of Danish energy experts proposed that Denmark should convert the supply of a specific town to 100% renewable energy by 2015. The experts suggested Frederikshavn in the northern part of Denmark for the following reasons. The town area of 25,000 inhabitants is well defined, the local support is high, and Frederikshavn already has a number of large wind turbines at the harbor. In February 2007, the city council unanimously decided to go for the project and set up a project organization involving utilities and municipality administrators. The local industry and the Aalborg University are also involved in the project. This chapter presents the methodology of mapping the existing energy system, including transport, and defining the share of renewable energy, which is approximately 20% at present. It introduces a proposal for a potential 100% renewable energy system for the year 2015 and a number of realistic short-term first steps, which will raise the share of renewable energy in Frederikshavn to approximately 40% by 2009 or 2010. This chapter describes detailed hour-by-hour energy system analyses of the proposal for a 100% renewable energy system. Also, it relates the proposal to the perspective of converting Denmark to a 100% renewable energy supply system.

This editorial introduces the content of selected papers from the 2nd International Conference on Smart Energy Systems and 4th Generation District Heating. 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 with a focus on the important role of district heating and cooling technologies.

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 solu- tions, 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.

In Denmark expansion of on-shore, near-shore and off-shore wind power is planned to increase the wind power share to 50% of electricity consumption by 2020. In this situation a continuation of past policies will not suffice, and a dual-track incentive system that both establishes incentives for investing in wind power and integration infrastructure with integration between the electricity, heating and transportation sectors, is required. The current Danish taxation system discourages electricity use and works against this integration. Likewise, the current day-ahead electricity spot market is not appropriate for a high-wind future as wind reduces price levels, but integration across sectors can partly assist in increasing demand and prices. The European Emission Trading System does not suffice in providing a level playing field for wind power and thus needs a revision. Another barrier for on-shore and near-shore wind power expansion is a growing citizens’ resistance due to an unequal distribution of benefits and burdens. Ownership should be open for more types of investors – especially local investors – in order to ensure public support and local acceptance of wind power projects. The Danish political system needs to address these issues in order to promote further expansion of wind power in Denmark.

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.Keywords: energy system analysis; investment optimisation models; simulations models; modelling theory;renewable energy

The aim of this article is to assess the potential of flexible demand in a far future energy system. Flexible energy systems are imperative for more integration of fluctuating renewable energy sources (RES) and therefore flexible demand as a flexible measure becomes more significant. Denmark is a leading country for high share of wind power in its electricity production and has announced to become a non-fossil fuel using country by 2050. In this article, Denmark is seen as a case due to this ambitious national goal, but the validity of the object of the analyses is not restricted to Denmark. The energy system simulated in this article is based on a Danish government year 2050 scenario based solely on RES. The article adopts two approaches for the assessment of the potential of flexible demand. The first approach is a bottom-up technical approach investigating the potential of flexible demand from individual processes. Secondly, the level of flexible demand which makes a significant impact on the future energy system is assessed with a view to investigating whether the two approaches will ever meet and thus whether flexible demand has a significant role to play in the future energy system. The results show that the potential of flexible demand is only found in the 2 h time frame with 24% and the daily time frame with approx. 7% of the electricity demand. The system benefit at the assessed amount of flexible demand is limited however. Results from the other analysis indicate that in order to have a significant impact on the energy system performance, more than a quarter of the classic electricity demand would need to be flexible within a month, which is highly unlikely to happen. The value of flexible demand in the energy system is thus limited.

The objective of this article is to show the potential of natural ventilation as a passive cooling method within the residential sector of countries which are located in warm conditions using Mexico as a case study. The method is proposed as performing, with a simplified ventilation model, thermal–airflow simulations of 27 common cases of dwellings (considered as one thermal zone) based on the combination of specific features of the building design, occupancy and climate conditions. The energy saving potential is assessed then by the use of a new assessment method suitable for large-scale scenarios using the actual number of air-conditioned dwellings distributed among the 27 cases. Thereby, the energy saving is presented as the difference in the cooling demand of the dwelling during one year without and with natural ventilation, respectively. Results indicate that for hot-dry conditions, buildings with high heat capacity combined with natural ventilation achieve the lowest indoor temperature, whereas under hot-humid conditions, night ventilation combined with low heat capacity buildings present the best results. Thereafter, an average aggregated saving potential of 4.2 TW h for 2008 is estimated, corresponding to 54.4% of the Mexican electric cooling demand for the same year. The practical implications of the study are that the results contribute to an assessment of the economic and environmental benefits for using natural ventilation rather than an active method such as air conditioning. Thereby, the average economic saving is estimated at US$ 900 M and the environmental benefit at an annual average mitigation of 2 Mt CO 2 eq, both for 2008.

Climate change and energy security are forcing Hong Kong to shift from a fossil fuel-based to a clean and low-carbon energy structure. In this article, a simulation model for Hong Kong's energy system is developed to examine the present energy structure and analyse alternative future sustainable energy strategies. First, a reference model is established and validated based on year 2009 data. Secondly, three scenarios are modelled. The BAU (business-as-usual) scenario for Hong Kong's energy system in 2020 is presented and simulated. To address the energy security and environmental sustainability challenges posed by the BAU outcomes, two alternative scenarios are then studied. The first alternative is a fuel mix for 2020 proposed by the government which is characterized by importing more nuclear power from the mainland. As a result of the Fukushima nuclear incident, however, this proposal has been held in abeyance. Therefore, a second alternative for Hong Kong in 2020 is proposed in this study, using more RE (renewable energy) to replace nuclear power. The results show that both the governmentally proposed scenario and the RE scenario can achieve the carbon reduction target. However, the RE scenario would be much better than the government scenario in terms of environmental, social benefits and long-term sustainability.

Islands typically have sensitive energy systems depending on natural surroundings, but innovative technologies and the exploitation of renewable energy (RE) sources present opportunities like self-sufficiency, but also challenges, such as grid instability. Samsø, Orkney, and Madeira are in the transition to increase the RE share towards 100%—however, this is addressed in different ways depending on the local conditions and current development phases in the transition. Scenarios focusing on the short-term introduction of new technologies in the energy systems are presented, where the electricity sector is coupled with the other energy sectors. Here, both smart grid and sector-integrating solutions form an important part in the next 5−15 years. The scenarios are analyzed using the modeling tool EnergyPLAN, enabling a comparison of today’s reference scenarios with 2030 scenarios of higher RE share. By including three islands across Europe, different locations, development stages, and interconnection levels are analyzed. The analyses suggest that the various smart grid solutions play an important part in the transition; however, local conditions, sector integration, and balancing technologies even more so. Overall, the suggestions complement each other and pave the way to reach 100% RE integration for both islands and, potentially, other similar regions.

Denmark has more than 10 years’ of experience with a wind share of approximately 20 per cent. During these 10 years, electricity markets have been subject to developments with a key focus on integrating wind power as well as trading electricity with neighbouring countries. This article introduces a methodology to analyse and understand the current market integration of wind power and concludes that the majority of Danish wind power in the period 2004–2008 was used to meet the domestic demand. Based on a physical analysis, at least 63 per cent of Danish wind power was used domestically in 2008. To analyse the remaining 37 per cent, we must apply a market model to identify cause–effect relationships. The Danish case does not illustrate any upper limit for wind power integration, as also illustrated by Danish political targets to integrate 50 per cent by 2020. In recent years, Danish wind power has been financed solely by the electricity consumers, while maintaining production prices below the EU average. The net influence from wind power has been as low as 1–3 per cent of the consumer price. Keywords: Wind power, Wind power integration, Wind power cost, Energy system analysis, Electricity markets

Nepal is heavily dependent on the traditional energy sources and imported fossil fuel, which has an adverse impact on the environment and economy. Renewable energy technologies promoted in the country are regarded as a means of satisfying rural energy needs of the country for operating different rural end-uses. In this context, this article is prepared to investigate energy alternatives to pump drinking water in one of the remote rural village of Nepal, which has no means of running water source. Analyses in this article are based on the formulation of three technical scenarios of water pumping using petro-diesel, jatropha-based biodiesel and solar photovoltaic pumps. The technical system design consists of system sizing of prime mover (engine, solar panel and pumps) and estimation of reservoir capacity, which are based on the annual aggregate water demand modelling. With these investigations, detailed financial modelling is carried out in a spreadsheet to compare the alternatives on the basis of the economic parameters; net present value, equivalent annualised cost and levelised cost of water pumping. Analysis is carried out considering different influential parameters; water head, discharge, incentives on the investments, which have effects on the cost of pumped water. Likewise, in case of biodiesel-based system, different yield rate of jatropha plants is also considered in estimating the cost of producing biodiesel. It is found that for operating a biodiesel-based pumping system for the study area, the levelised cost of pumping 1 L of water is higher than that of a solar pump and even higher when compared with diesel, if the seed yield per plant is less than 2 kg and without subsidy on the investment cost of cultivation and processing. With the productivity of 2.5 kg/plant, a biodiesel-based system is more attractive than that of the diesel-based pump, but still remains more expensive than that of solar pump. From the technical perspective (reliability and easiness in operation) and economic evaluation of the technical alternatives, solar pumping system is found to be the most viable solution to pump drinking water in the project area.

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.

Scenario-making is becoming an important tool in energy policy making and energy systems analyses. This article probes into the making of scenarios for Denmark by presenting a comparison of three future scenarios which narrate 100% renewable energy system for Denmark in 2050; IDA 2050, Climate Commission 2050, and CEESA (Coherent Energy and Environmental System Analysis). Generally, although with minor differences, the scenarios suggest the same technological solutions for the future such as expansion of biomass usage and wind power capacity, integration of transport sector into the other energy sectors. The methodologies used in two academic scenarios, IDA 2050 and CEESA, are compared. The main differences in the methodologies of IDA 2050 and CEESA are found in the estimation of future biomass potential, transport demand assessment, and a trial to examine future power grid in an electrical engineering perspective. The above-mentioned methodologies are compared in an evolutionary perspective to determine if the methodologies reflect the complex reality well. The results of the scenarios are also assessed within the framework of “radical technological change” in order to show which future scenario assumes more radical change within five dimensions of technology; technique, knowledge, organization, product, and profit.

This article presents a model of natural ventilation of buildings at the stage of design and a consequence of the behaviour of the occupants. An evaluation is made by coupling multizone air modelling and thermal building simulation using a deterministic set of input factors comprising among others climate, local environment, building characteristics, building systems, behaviour of occupants and heat loads. Selected deterministic input factors are varied to generate additional information applied in an optimization loop. With that, it is found that the optimal solution depends to a great extent on the possibility of optimization of the behaviour of occupants, and to a lesser extent on the design of the building.

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.

Increasing penetration of fluctuating energy sources for electricity generation, heating, cooling and transportation increase the need for flexibility of the energy system to accommodate the fluctuations of these energy sources. Controlling production, controlling demand and utilising storage options are the three general categories of measures that may be applied for ensuring balance between production and demand, however with fluctuating energy sources, options are limited, and flexible demand has also demonstrated limited perspective. This article takes its point of departure in an all-inclusive 100% renewable energy scenario developed for the Danish city Aalborg based on wind power, bio-resources and low-temperature geothermal heat. The article investigates the system impact of different types of energy storage systems including district heating storage, biogas storage and electricity storage. The system is modelled in the energy systems analyses model energyPRO with a view to investigating how the different storages marginally affect the amount of wind power that may be integrated applying the different storage options and the associated economic costs. Results show the largest system impact but also most costly potential are in the form of electricity storages.

Aalborg Municipality, Denmark, wishes to investigate the possibilities of becoming independent of fossil fuels. This article describes a scenario for supplying Aalborg Municipality’s energy needs through a combination of low-temperature geothermal heat, wind power and biomass. Of particular focus in the scenario is how low-temperature geothermal heat may be utilised in district heating (DH) systems. The analyses show that it is possible to cover Aalborg Municipality’s energy needs through the use of locally available sources in combination with significant electricity savings, heat savings, reductions in industrial fuel use and savings and fuel-substitutions in the transport sector. With biomass resources being finite, the two marginal energy resources in Aalborg are geothermal heat and wind power. If geothermal heat is utilised more, wind power may be limited and vice versa. The system still relies on neighbouring areas as an electricity buffer though.The costs of the scenario are at a comparable level with the reference situation, but with significantly higher needs for investments and lower fuel costs. Implementation of the scenario would therefore have a positive socio-economic impact as investments are more local labour-intensive than fuel supply. Aalborg Municipality, Denmark, wishes to investigate the possibilities of becoming independent of fossil fuels. This article describes a scenario for supplying Aalborg Municipality’s energy needs through a combination of low-temperature geothermal heat, wind power and biomass. Of particular focus in the scenario is how low-temperature geothermal heat may be utilised in district heating (DH) systems. The analyses show that it is possible to cover Aalborg Municipality’s energy needs through the use of locally available sources in combination with significant electricity savings, heat savings, reductions in industrial fuel use and savings and fuel-substitutions in the transport sector. With biomass resources being finite, the two marginal energy resources in Aalborg are geothermal heat and wind power. If geothermal heat is utilised more, wind power may be limited and vice versa. The system still relies on neighbouring areas as an electricity buffer though.The costs of the scenario are at a comparable level with the reference situation, but with significantly higher needs for investments and lower fuel costs. Implementation of the scenario would therefore have a positive socio-economic impact as investments are more local labour-intensive than fuel supply.

Denmark is in a situation with many scattered sources of electricity that are not controlled by the central load dispatch. At the same time, Denmark is being used as an electricity transit corridor between the hydro-based systems of Norway/Sweden and the thermal systems of Germany and continental Europe. Through energy systems analyses and load-flow analyses, it is determined that if geographically scattered load balancing utilising the regulation ability of hitherto locally controlled plants is introduced while also introducing new dispatchable loads in the form of electric vehicles and heat pumps, electricity transit is enabled to a higher degree than if central load balancing is maintained. This is the case of an intact transmission system as well as a system with inoperative transmission lines. With an intact system, the average load of the system is approximately halved when applying scattered load balancing. Utilising the regulating capacity of local plants thus improves the role of the Danish system in the Northern European system.

At modest penetration, wind power merely substitutes electricity generated typically at thermal power plants. In this case, wind power only provides economic benefits in terms of saved marginal fuel and operation and maintenance costs. At higher penetrations, it becomes increasingly important for the energy system to be able to operate without costly reserve capacity awaiting fluctuations in demand or wind power generation. Existing transmission interconnections have mainly been established in order to assist in reducing the reserve capacity of thermal power systems. While indeed relevant in thermal systems, this is typically even more important in renewable energy-based systems, in which fluctuations to a large extent are uncontrollable. This makes interconnected systems an interesting option for integrating electricity produced from such energy sources. Using a Danish example, this article demonstrates how different demand and wind production variations in different geographical areas assist in evening out fluctuations and reducing imbalances in systems with high penetrations of wind power. By exploiting these variations, the needs for reserve capacity and condensing mode power generation are reduced. However, the article also demonstrates that there are limits to what can be gained on this account.

The Mexican electricity consumption is highly based on fossil fuels. In 2012 only 15% of the electricity generation was produced using renewable energy sources (RES) and most of the new installed capacity during the last decade has been based on combined cycle power plants. On the other hand, Mexico is a land of ample opportunities for renewable energy exploitation that could lower its dependency on fossil fuels. Recently, the Mexican Congress approved a regulation limiting fossil fuel-based electricity generation to 65% by the year 2024, to 60% by 2035 and to 50% by 2050. In this work the authors investigate the potential for renewable energy integration into the Mexican electricity system. The authors construct three scenarios (low, mid and high biomass) for achieving the 2024 target and analyse the electricity system response to varying contributions of wind and solar power production to the scenarios. The minimum complementary capacity based on fossil fuels needed to cover the demand without electricity imports is also assessed. Results indicate that within each scenario several combinations of bio, wind and solar power make a minimum of 35% RES electricity production possible. However, in every scenario there is only one combination resulting in the minimum overall capacity. Biomass has the highest effectiveness in terms of high RES production with the lowest needed overall power generating capacity.

Energy systems with high degrees of renewable energy integration require on the one hand energy scenario making and energy system analyses for the optimal design of systems and pathways and on the other hand well-established criteria for decision-making and for characterisation of energy system suitability. This article has a threefold objective, it reviews the application of a given energy system simulation model – EnergyPLAN – analysing its application on geographic level as well as the types of simulations or scenario analyses performed on the model. Secondly, it reviews the types of performance indicators applied in said energy systems simulations and thirdly it reviews and details existing advanced energy system performance indicators and proposed additional indicators.

Six different strategies have recently been proposed for the European Union (EU) energy system in the European Commission's report, Energy Roadmap 2050. The objective for these strategies is to identify how the EU can reach its target of an 80% reduction in annual greenhouse gas emissions in 2050 compared to 1990 levels. None of these scenarios involve the large-scale implementation of district heating, but instead they focus on the electrification of the heating sector (primarily using heat pumps) and/or the large-scale implementation of electricity and heat savings. In this paper, the potential for district heating in the EU between now and 2050 is identified, based on extensive and detailed mapping of the EU heat demand and various supply options. Subsequently, a new ‘district heating plus heat savings’ scenario is technically and economically assessed from an energy systems perspective. The results indicate that with district heating, the EU energy system will be able to achieve the same reductions in primary energy supply and carbon dioxide emissions as the existing alternatives proposed. However, with district heating these goals can be achieved at a lower cost, with heating and cooling costs reduced by approximately 15%. Six different strategies have recently been proposed for the European Union (EU) energy system in the European Commission's report, Energy Roadmap 2050. The objective for these strategies is to identify how the EU can reach its target of an 80% reduction in annual greenhouse gas emissions in 2050 compared to 1990 levels. None of these scenarios involve the large-scale implementation of district heating, but instead they focus on the electrification of the heating sector (primarily using heat pumps) and/or the large-scale implementation of electricity and heat savings. In this paper, the potential for district heating in the EU between now and 2050 is identified, based on extensive and detailed mapping of the EU heat demand and various supply options. Subsequently, a new ‘district heating plus heat savings’ scenario is technically and economically assessed from an energy systems perspective. The results indicate that with district heating, the EU energy system will be able to achieve the same reductions in primary energy supply and carbon dioxide emissions as the existing alternatives proposed. However, with district heating these goals can be achieved at a lower cost, with heating and cooling costs reduced by approximately 15%.

In energy dependent economies, energy consumption is often linked with the growth in Gross Domestic Product (GDP). Energy intensity, defined herewith, as the ratio of the total primary energy consumption (TPE) to the GDP, is a useful concept for understanding the relation between energy demand and economic development. The scope of this article is to assess the future primary energy consumption of Nepal, and the projection is carried out along with the formulation of simple linear logarithmic energy consumption models. This initiates with a hypothesis that energy consumption is dependent with the national macro-economic parameters. To test the hypothesis, nexus between energy consumption and possible determinant variables are examined. Status of energy consumption between the period of 1996 and 2009, and for the same period, growth of economic parameters are assessed. Three scenarios are developed differing from each other on the basis of growth rates of economic indicators: total GDP, GDP-agriculture, GDP-trade, GDP-industry, and other variables including growth in private consumptions, population, transport vehicles numbers, prices of fossil fuels etc. Scenarios are: Business as Usual (BAU), Medium Growth Scenario (MGS) and High Growth Scenario (HGS). Energy consumption in all the sectors and for all fuel types are not statistically correlated with every economic parameters tested in the assessment. Hence, the statistically correlated models are included in the prognosis of energy consumption. For example, the TPE consumption and electricity consumption, both are significantly dependent with the total GDP and population growth. Likewise, fuel wood consumption is significantly dependent with the growth in rural population and private consumptions. In BAU the estimated electricity consumption in 2030 would be 7.97 TWh, which is 3.47 times higher than that of 2009. In MGS, the total electricity consumption in 2030 is estimated to increase by a factor of 5.71 compared to 2009. Likewise, in HGS, electricity consumption would increase by 10-fold until 2030 compared to 2009, demanding installed capacity of power plant at 6600 MW, which is only from hydro power and other centralised system.