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This review article addresses the status of research within the application of renewable energy sources. It focuses on the status of renewable technologies, the role of renewable energy sources in meeting sustainable development goals, the status of the research into the sustainability of the renewable energy systems, and finally on the integration of renewable energy technologies in low carbon energy systems. Regarding renewable resources and technologies, wind and wave power resource assessment, heating and cooling, solar energy, renewable energy fuels, and integrated energy systems are reviewed and summarized. The article takes a starting point in work presented at the conference series on Sustainable Development of Energy, Water and Environmental Systems (SDEWES), published in the Renewable Energy journal and puts this work into a broader context. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. • Review of recent developments in renewable energy technology. • Unexploited potentials for renewable energy exploitation identified. • Systems analyses indicate good prospects for transforming energy systems. [ABSTRACT FROM AUTHOR]

This article examines some of the latest findings in the exploitation of renewable energy sources (RES) for sustainable development. It outlines some of the latest findings at the system level – e.g., local systems, community systems, and assemblies of buildings – as well as some of the main components in future renewable energy systems. This includes solar technologies, where particular attention is given to the cooling of photovoltaic panels to improve conversion efficiency. Hydrogen – in one way or the other – will play a role as a storage medium or as a means of electrifying otherwise hard-to-electrify sectors. Bioenergy is a valuable but restricted source in the energy system, hence different processes are investigated to optimize the use of different biomass waste streams. Lastly, wind power is addressed as one of the key constituents of future renewable energy-based energy systems. In this special issue, the focus, however, is on the end-of-life handling of turbine blades. [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]

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. [ABSTRACT FROM AUTHOR]

Electricity generation from photovoltaic (PV) plants plays a major role in the decarbonization of the energy sector. The core objective of this paper is to identify the most important conditions for the future development of PV in order to achieve its greatest possible benefits of PV systems for society. This analysis is based on the documentation of the historical deployment of quantities of PV and on the lessons learned regarding cost developments. In addition, the improvements of PVs technical and environmental performance parameters are investigated. A major result is that the impact of PV feed-in on network capacities may be substantial. Hence, classical energy-based network charges are inadequate. Changes in tariff and pricing structures are needed especially on retail level. The major conclusions is that customers should also receive time-variable price signals that tells them the real-time value of electricity in the system and provides incentives for taking electricity from the grid or feed-in. In addition, the tariffs should have components for maximum power from and to the grid. Another conclusion is that on retail level grid parity already today provides sufficient incentives to purchase a PV system in many countries without additional financial support. • The 4 major Highlights of this paper are: • Grid parity has made PV systems economically attractive already in many countries. • Grid parity has reduced the need for subsidies for small decentralized systems. • Retail pricing systems providing fair conditions for all customers are needed. • Final customers tariffs should include components for power from and to the grid. [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]

Following the 2015 Paris Agreement and other agreements which have been signed after, sustainable energy development is becoming the major goal in many countries. EU have set the targets to reduce the annual greenhouse gas emission by 40% in 2030 and 80% for 2050 compared with 1990 levels. For achieving this ambitious energy policy, three major technological changes are available: energy savings on the demand side, efficiency improvements in the energy production, and replacement of fossil fuels by various sources of renewable energy. Also, for realization cited three major technological changes the support of the multi-disciplinary scientific knowledge is needed. Therefore, from the beginning of the 21st century, since 2002, a series of Sustainable Development of Energy, Water and Environment Systems (SDEWES) Conferences were founded. This paper presents an overview of published researches in special issues of leading journals dedicated to the series SDEWES Conferences, including also the papers in current special issue. The focus is on five main fields: (1) energy policy and analysis of smart energy systems; (2) energy savings in the building sector; (3) co/polygeneration - integrated heating, cooling and electricity systems and district heating; (4) biomass for energy; and (5) measurement of energo-environmental sustainability of processes and systems. Researchers are focused on the development of methods, policies and technologies for both efficient production of energy, mainly from renewable sources, and consumption in industry, buildings and transport. Undoubtedly, the researches presented in the papers in this special issue as well as in previous ones, dedicated to SDEWES conferences, will contribute to the promotion of sustainable development and thus to the achievement of the goals of the Paris Agreement. [ABSTRACT FROM AUTHOR]

Abstract: Increase of the global energy demand and environmental problems relating to fossil energy utilization request the new energy sources to replace the traditional fossil fuels. With respect to energy production, most of the islands in European Union and in the other parts of the world, depend on importation, mainly from oil and its related products. The global development of renewable energy technologies can assure sustainable supply of power for islands. To overcome the limitation of the sources of renewable energy, hydrogen is utilized as a storage medium integrated with intermittent renewable energy sources such as wind and solar. This paper introduces the programme of “Renewislands—Renewable Energy Solutions for Islands”, the work tasks, details of the design of the activities to develop solutions integrating intermittent renewable energy supply (RES), fuel cell (FC) and hydrogen infrastructure to promote RES and innovative decentralized power systems penetration in islands; main results achieved in each work packages are presented; in addition, the development of intermittent renewable energy penetration in specific European Islands are reviewed briefly. [Copyright &y& Elsevier]

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. [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]

A smart municipal energy grid including electricity and heat production infrastructure and electricity demand response has been modeled in HOMER case study with the aim of decreasing total yearly community energy costs. The optimal configurations of used technologies (photovoltaic plants, combined heat and power plants, wind power plants) and sizing, with minimal costs, are presented and compared using three scenarios of average electricity market price 3.5 c€/kWh, 5 c€/kWh and 10 c€/kWh. Smart municipal energy grids will have an important role in future electricity markets, due to their flexibility to utilize excess electricity production from CHP and variable renewable energy sources through heat storage. This flexibility enables the levelized costs of energy within smart municipal energy grids to decrease below electricity market prices even in case of fuel price disturbances. With initial costs in the range 0–3,931,882 €, it has been shown that economical and environmental benefits of smart municipal energy grids are: the internal rate of return in the range 6.87–15.3%, and CO2 emissions in the range from −4,885,203 to 5,165,780 kg/year. The resulting realistic number of hours of operation of combined heat and power plants obtained by simulations is in the range 2410- 7849 h/year. [ABSTRACT FROM AUTHOR]

Geothermal energy is a widely available renewable energy source. In Croatia geological data have been indicating promising potential, especially in the North-Eastern part of the country with a geothermal gradient higher than 49 °C/km and terrestrial heat flux of 76 mW/m 2 . Nonetheless, despite this potential, this resource is not highly exploited to date. Efficient use of geothermal energy can contribute on reducing Croatia’s energy dependence. In this paper, a methodology of a possible integration of geothermal energy within residential, commercial and industrial systems was attempted. Pinch analysis was used to find the best ways to fulfil the energy system requirements in an efficient, clean and cost-effective way. The used approach gives a good overall picture of energy targets for process, site and utility levels. The recommendation for cost-effective integration of geothermal energy into regional energy network is considered by use of Pinch Analysis. Additional attention was paid to geothermal energy utilisation in low enthalpy sedimentary environments. The obtained results can be used for integration of geothermal energy in different cases and “countries”. It gives general recommendation for geothermal sources placement as well as for energy planning and regional sustainability. [ABSTRACT FROM AUTHOR]

Global warming concerns have driven developments in carbon neutral energy, pulling initiatives on biofuels production. However, the low bulk density and low specific energy of biomass refrain its widespread use due to logistic costs comprising harvesting and collection, storage, pretreatments and transportation. This work approaches increasing land energy productivity by thermochemical conversion of residual biomass to energy products, identifying the best options in terms of energy efficiency and economic indicators. Techno-economic performance of three corncob-to-energy pathways is investigated: gasification to methanol, fast pyrolysis to bio-oil and combustion to electricity. Fast pyrolysis allows higher energy recovery in its products (79%) than biomass gasification to methanol (53%), with biomass densification (volume reduction) of 72.7% and 86.2%, respectively. The combustion route presents net efficiency of 30.2% of biomass low heating value (LHV). All alternatives are economically feasible provided biomass cost is lower than US$75.5/t. The minimum allowable product prices for economic attractiveness of gasification, combustion and pyrolysis routes are US$305/t methanol, US$80.1/MWh electricity and US$1.47/gasoline-gallon-equivalent bio-oil. Despite its vulnerability to price volatility, gasification presents the highest net present value, seconded by the combustion route, which has lower medium-term payback and investment than gasification due to its process simplicity. Unlabelled Image • Three thermochemical processes for energy densification of corncob are compared. • Pyrolysis has highest energy efficiency, lowest CO 2 emissions and shorter payback. • Net Present Values decrease from combustion to gasification and then pyrolysis. • All Net Present Values are positive provided biomass costs below US$75.50/t. • Bio-oil price above US$18/t renders pyrolysis the best economic alternative. [ABSTRACT FROM AUTHOR]

Abstract Energy use in cities has attracted significant research in recent years and city level energy planning is becoming a required task driven by the contribution of decentralized renewable electricity production and a demand-side approach towards greenhouse gases emissions reduction. However, traditional energy planning approaches are limited because they tend to focus on technology substitution. We argue that a more ambitious and holistic urban energy planning approach is desirable. This paper proposes a novel method to integrated Energy and Urban Planning solutions assessment by modelling and quantifying urban energy planning strategies impact in terms of energy savings, greenhouse gases emission reduction and in increasing cities renewable distributed and local energy generation. We apply the approach to São Paulo megacity using the LEAP_SP urban energy simulation model (from 2014 to 2030) through four scenarios. Results showed that by using a traditional energy planning approach, it is possible to reach 2% energy savings from the current situation, 18% greenhouse gas emission reduction and a three-fold increase in renewables deployment. When applying only urban planning strategies these benefits are of 10% energy savings, 8% greenhouse gas emission reduction and one-fold increase in renewables deployment. If a more holistic urban energy approach is adopted by integrating both energy and urban planning policies, gains increase to 12% energy savings, 30% greenhouse gases emission reductions, and a four-fold increase in renewable distributed and local electricity generation from the current city status. Graphical abstract Image 102680 Highlights • Integrated Urban Energy Planning Strategies for new and established cities. • São Paulo city real data multisectoral Urban Energy System development. • Assess the benefits of combining urban and energy planning strategies. • Urban Energy Planning strategies integration creates substantial synergies. • Major impact of urban energy planning strategies is for GHG emission reduction. [ABSTRACT FROM AUTHOR]

Abstract This review article presents a description of contemporary developments and findings related to the different elements needed in future 4th generation district heating systems (4GDH). Unlike the first three generations of district heating, the development of 4GDH involves meeting the challenge of more energy efficient buildings as well as the integration of district heating into a future smart energy system based on renewable energy sources. Following a review of recent 4GDH research, the article quantifies the costs and benefits of 4GDH in future sustainable energy systems. Costs involve an upgrade of heating systems and of the operation of the distribution grids, while benefits are lower grid losses, a better utilization of low-temperature heat sources and improved efficiency in the production compared to previous district heating systems. It is quantified how benefits exceed costs by a safe margin with the benefits of systems integration being the most important. Highlights • Provides a review of 4th Generation District Heating (4GDH) in scientific papers. • Shows how 4GDH is an important integrated part of future sustainable energy systems. • Quantifies costs and benefits of 4GDH in a future sustainable energy system. • Shows how benefits exceed costs by a safe margin. • Shows the significant benefits of systems integration. [ABSTRACT FROM AUTHOR]

Small Islands usually rely on fossil fuels for their energy supply and face common challenges such as high energy costs and carbon dioxide emissions. For these reasons they represent interesting cases for analysing the transition towards a clean and secure energy system. Nevertheless, integrating non-dispatchable Renewable Energy Sources in the power grid causes stability issues and this is particularly true for island grids. Such issue is not fully considered in long-term energy planning; indeed, an important factor that should be considered in order to ensure the reliability of the grid are Reserves. There are different types of Reserves depending on the reactiveness/response time and the duration of the service. In this paper, primary and secondary reserves have been analysed in order to plan the long-term energy transition of the small island of Favignana, Italy by means of the new version of H2RES, a Linear Programming single-objective optimisation model able to provide a long-term capacity investment and dispatching optimisation. It has been found that biomass generators are favoured to both photovoltaic and wind turbines for their ability to provide reserves and also decrease the unpredictability of the supply. Batteries and Electrolysers are also used mostly for reserve provision. • Primary and Secondary Reserves are embedded in long-term optimisation model. • Optimal energy Transition strategy towards Smart Island Energy System is found. • Biomass is the main renewable source since it reduces reserve requirement. • Electrolysers are operated for 85% of their usage time as downward reserve provider. [ABSTRACT FROM AUTHOR]

Due to the stochastic nature and variability of renewable energy sources (RES), it is necessary to integrate still expensive storage capacities into an energy system with a high share of RES and to model appropriate energy market. The study presented here considers all energy carriers, however, only the electricity carrier is modeled in detail, with notion taken for the heating demand that is covered but without proper modeling of storage. A proposed two-level approach with multi-objective optimization on the global level, was used to design a Croatian Energy System (CES), where electric vehicles (EVs) are integrated to serve as battery storage in Vehicle-to-Grid (V2G) mode, for a scenario between 2015 and 2050. In addition, case study includes nine aggregated hydro power plants, one for each river basin in Croatia. Also, case study includes solar and wind power plants modeled for six locations in Croatia: Osijek, Zagreb, Rijeka, Sibenik, Split and Dubrovnik. The resulting Pareto front suggests that with assumed future costs of fuels and technology certain level of conventional energy sources will have to remain in the energy system to take into the account unfavourable weather conditions and to cover heating demand, which also results in significantly lower load factors for those power plants. Also, variants with more RES share have lower total energy system load factor and significantly higher installed capacity. [ABSTRACT FROM AUTHOR]

The goal of this paper is to showcase a modelling exercise, conducted for the Republic of Macedonia, a non-Annex I country under UNFCCC and a candidate for EU membership, by making use of MARKAL energy system model. Baseline Scenario and three groups of mitigation scenarios have been developed until 2050, reflecting different types of targets with different levels of ambition regarding CO 2 emissions reduction: (1) EU scenarios – end-year targets compared to 1990 level; (2) QELRC (Quantified Emission Limitation and Reduction Commitment) scenarios – a range of targets over the period 2021–28 and for each subsequent 8-year period, and (3) Baseline deviation scenarios – deviation compared to baseline emission level. The comparative assessment of mitigation scenarios, based on the cumulative emissions, cumulative total system costs and incremental specific reduction cost, has generated a basis for setting the national mitigation contributions and formulating the most appropriate national mitigation action plan. [ABSTRACT FROM AUTHOR]

Abstract: As forecasted by the International Energy Agency Energy Technology Perspectives baseline scenario, the largest increment in LDV (light-duty vehicles) stock, travel demand and transport sector energy consumption will take place in the developing world. In the developing countries where the import of used vehicles is allowed, a considerable portion of the LDV stock increment will be realized with used vehicles. In this paper, the analytical framework for assessment of climate change mitigation potential of transport sector in developing countries is adapted in order to incorporate the expected vehicle fleet increase with used vehicles. The evaluation of appropriate mitigation strategies is performed using the GHG Costing Model (GACMO), which compares each mitigation option with the BAU (business-as-usual) option and determines its environmental effectiveness (t CO2 reduced) and economic effectiveness (US$/t CO2 reduced). The adapted analytical framework is applied on the case of transport sector of Macedonia, evaluating appropriate options inline with five mitigation strategies: improvement of vehicle fleet, introduction of low carbon fuels, improvement of travel behaviour, advancement of vehicle equipment and improvement of driver behaviour. The resulting marginal cost curve for the year 2020 indicates a total achievable reduction of 22% with respect to BAU GHG transport sector emissions, with bulk of it at relatively high specific costs of around 90 US$/t CO2. [Copyright &y& Elsevier]

Abstract: The increase in PV (photovoltaic) capacities in Germany had since 2011 on some days already significant impacts on spot market prices at the German electricity exchange. The core objective of this paper is to investigate the possible effects of a further uptake of PV on the prices in electricity markets. We analyze two major effects: (i) the direct impact of PV at specific times of the year when PV shifts the supply curve of conventional electricity virtually out of the market, leading to temporarily very low market prices close to Zero; (ii) the indirect impact of PV (and wind) on the costs at which fossil capacities are offered at times when renewable energy sources are scarce. The major effects of these developments on the electricity markets will be: (i) a much higher price volatility from hour-to-hour and day-to-day; (ii) higher prices for electricity from fossil capacities and storage technologies for balancing the intermittent renewable generation; and (iii) growth of balancing markets and intensified competition at the level of decentralized balancing organizations. [Copyright &y& Elsevier]

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]