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The requirements for ancillary services in energy systems are growing as the amount of renewable energy sources such as solar and wind increases. On the other hand, the system can benefit from extra sources of flexibility thanks to the increased digitalization that enables successful integration of demand response and energy storage. The majority of recent energy system analysis research did not consider the regulation markets. As a result, these investigations preclude the ability to fully evaluate the advantages of energy storage and flexible cooling loads. With the method outlined in this paper, it is possible to compare the two strategies and assess the advantages of energy storage and flexible cooling loads for each strategy. In addition to the energy storage systems, the case study in this paper focuses on flexible cooling loads as a significant consumer in the system. According to the findings, the system's operating costs increased by 19.4% when reserve limitations were placed. Furthermore, the findings demonstrated that when flexible assets were permitted to participate in the reserve market, they generated significantly higher incomes. According to the findings, mechanisms that will allow energy storage and demand response to provide reserve capacities as well as the growth of reserve markets are both necessary.

Background A sustainable energy system based on renewables, energy-efficiency, decentralisation of energy generation and synergies between different sectors requires new energy planning methods and policies. Energy transition and climate change mitigation achievement can no longer be seen only through top-down activities from a national government. Local and regional governments have a crucial role in delivering public policies relevant to such endeavour. Therefore, the implementation of multilevel governance (MLG) has become a priority for fostering local and regional development more inclusively. Paper analyses the existing energy planning governance in Austria throughout the MLG structure by focusing on the alignment between the local energy and climate initiatives and the national and EU goals. Also, the paper examined the effectiveness of the current MLG structures and outlined the fields where improvements are needed. The successfulness of the MLG approach is shown on Judenburg city case study. Desk research is enhanced by a series of interviews with energy policy experts and implementation of case study measures in TIMES model. Results The MLG analysis showed the solid alignment of different governance levels. In contrast, the comparison of the energy and climate initiatives on the local level outlined recommendations for the design of more effective energy planning approach. Four areas of action are identified for further improvement: territorial fragmentation, data availability, spatial energy planning and new integrated MLG. The remaining non-conventional biomass potential of the Murtal region is enough to increase the share of district heating for the residential buildings of the Judenburg city from 16.3 to 30.8% while the building refurbishment increases district heating share to 32%. Conclusion Application of MLG analysis demonstrated the alignment of energy targets in Austrian policy on different governance levels. The general willingness of Austrian municipalities to take part in local energy actions was shown through the local initiatives’ analysis. It is argued that strengthening the listed areas of work is necessary to raise the effectiveness of the local initiatives. The case study for the city of Judenburg developed in the TIMES model confirmed that coordinated actions from different levels of governance lead to effective implementation of measures.

The ongoing climate change, together with the global increase in energy consumption and unpredictable fossil fuel prices have been the main drivers for the implementation of power exchange, market coupling, energy efficiency measures and larger use of renewable energy. All these targets bring up the need for the development of new modelling frameworks and governance systems that will be based on competitive, secure and sustainable national action plans. For this purpose, the Dispa-SET model has been applied to six countries in the Western Balkans region. In the first scenario, the model has been validated for the year 2010. The second scenario has been developed according to the targets from national energy strategies for the years 2020 and 2030, while the third scenario has been developed with the purpose of determining the maximum share of renewable energy sources in the regional power mix. Simulation results indicate that the integration of additional wind and solar capacities, compared to the short and long-term national strategies for the years 2020 and 2030, can be achieved without compromising the stability of the system. ispartof: Journal of Sustainable Development of Energy, Water and Environment Systems vol:8 issue:1 pages:184-212 status: Published online

Heat and cooling stands out with the great potential in decarbonisation since they have a large share in the final energy consumption. Power-to-heat technologies may contribute to the heat sector decarbonisation as well as the integration of renewables if they are sufficiently flexible. They are also shown to have a good effect on the system costs. This work will analyse the potential of seawater heat pump system for the utilization of high share of electricity production from the renewables. The Old City of Dubrovnik is selected as a case study because of its specific situation. A large number of the outdoor units are not well approved by UNESCO since the Old City is under the protection of the UNESCO World Heritage Centre. The results of the study showed that the combination of wind and solar electricity production can cover 67% of load for stand-alone seawater heat pump system based on hourly time step. Utilization of renewable electricity generation, for this case, resulted in 433.71 tCO2/y emission reduction. System based on 10 minutes time step gave poorer results by 6%. System with the additional energy storage gained best results in the case of combined wind and solar electricity generation, as well. It resulted in storage capacity reduction by 78% ac-cording to the case of solar electricity generation and by 60% according to the wind electricity generation. Battery energy storage resulted in 40 times lower volume and 13 times higher investment costs and levelised cost of heat in comparison to the thermal energy storage.

The urgency of mitigating climate change comes with opportunities to transition society towards a more sustainable future. Numerous options exist for immediate, deep, and sustained efforts to realise a 43% reduction in greenhouse gas emissions by 2030. Beyond the recent reports of the Intergovernmental Panel on Climate Change, this editorial extends insight into new research advances for integrated approaches that can support effective climate mitigation. Based on the 16th Conference on Sustainable Development of Energy, Water, and Environment Systems, the review in this editorial interconnects the 28 research articles in this special issue within a broader context across eight main themes. The first theme on 100% renewable energy systems emphasizes recent advances in modelling and sector coupling, extending to the optimization of positive energy districts and energy communities at the local level and ultra-low temperature district heating and cooling networks. Energy security with sustainable energy solutions involves electrification, renewable energy, and energy savings. Transforming transport for energy transition solutions and new frontiers in renewable energy technologies cover advances for smart energy districts, electric vehicles, accurate forecasting of long-term wind speed, hydrogen propulsion in marine vessels, and innovations for water quality monitoring. System restructuring for the energy transition is supported with research contributions on time variability and environmental signalling in electricity markets, dedicated price structures for energy community trading, flexibilisation, and repurposing drilling sites for deep geothermal energy. Thematically, upgrading of biomass for biofuel production, green hydrogen innovations and heat transfer as well sustainable combustion complete the special issue. New catalysts, hybrid reaction for lignocellulosic biofuels, hydrogen fuel cell electrocatalyst, and waste heat recovery from granules in concentrating solar power or slags are some of the research advances under these themes. The widespread upscaling of solutions for mitigating climate change requires an effective approach that involves integrated, coordinated, and synergistic action now as the only chance for better protecting the life-support systems of the planet.

The paper shows the process of the development of the sustainable energy action plan (SEAP) for the city of Zagreb and analysis of the interaction between measures, which are used for the reduction in energy consumption and CO2 emissions. The energy savings and CO2 reduction potential of measures are compared in a scenario and individual approach. Sectors of energy consumption listed in SEAP are buildings, transport and public lighting. The buildings sector is divided into public buildings, residential and commercial buildings. The transport sector is subdivided on public transport, public vehicles and private and commercial transport. Measures for CO2 emission reduction are selected by a discussion with relevant stakeholders and most effective measures from the previous SEAP. Mutual interaction between measures, which influences the total result of energy consumption and CO2 emissions reduction, is done through simulation in LEAP. In this way, it can be shown that measures have either synergetic, negative or neutral interaction between them. The analysis showed the negative interaction is prevailing and scenario approach resulted in 16.23% lower CO2 reduction potential than the individual assessment of each measure. It is recommended to use a scenario approach in the development of SEAP for the assessment of measures CO2 reduction potential. This will provide more efficient planning of measures for the reduction in CO2 emissions on a local level and avoid overestimating of the CO2 reduction potential when developing SEAPs.

This present study offers a novel approach for the improvement of energy planning. This has become increasingly important as higher penetration of variable energy resources and increased interconnection between the different energy sectors require more detailed planning in terms of spatiotemporal modeling in comparison to the presently available approaches. In this study, we present a method that soft-linked the energy planning and power flow models, which enabled fast and reliable solving of optimization problems. A linear continuous optimization model was used for the energy system optimization and the non-linear problem for the power system analysis. The method is used to compare different energy planning scenarios; further, this also offers the possibility for implementation assessment of the proposed scenarios. The method was applied to interconnected islands for five different scenarios. It was determined that the detailed spatial approach resulted in 26.7% higher total system costs, 3.3 times lower battery capacity, and 14.9 MW higher renewable energy generation capacities installed than in the coarser spatial representation. Moreover, the results of the power flow model indicated that the highest voltage deviation was 16% higher than the nominal voltage level. This indicates the need for inclusion of implementation possibility assessments of energy planning scenarios.

Blue energy is one of the development sectors identified in the European Union strategic documents within the blue economy that promotes the exploitation of the sea potential. European energy initiatives recognize the importance of blue energy and encourage its research and development. The offshore exploitation of hydrocarbons worldwide is entering the final phase, followed by the gradual decommissioning of the production platforms and their removal. Decommissioning usually has an adverse effect on the environment aside from its economic intensity. By proper planning, lifetime of existing offshore infrastructure can be extended as it can be used for blue energy or other activities related to the blue economy. The paper deals with preliminary assessment of natural gas offshore infrastructure applicability for various blue energy options such as the wind power for electricity generation along with hydrogen, methane or ammonia production and other uses to reduce waste, energy consumption and CO2 emissions. Methods used included data gathering from 19 offshore gas facilities including assessment of natural gas production on current offshore fields, reserves and technology use, wind potential and decommissioning. Review of potential for energy production, storage and other activities such as CCS and CCU have also been given. Preliminary results show that there are possibilities for feasible and environmentally friendly blue energy utilisation. Average calculated capacity factors for the wind turbines are at the 32%. To investigate economic feasibility of decommission delay, detailed data gathering of wind potential should be done at specific heights along with load capacity of the gas platforms.

This study presents developed approaches that could be used for retrofitting of existing heat exchanger networks (HENs) within individual processes and industrial sites to achieve lower energy consumption, cost savings and emission reduction. Successful industrial applications are further presented, and future challenges are identified. Approaches used for retrofitting of existing HENs are based on heuristics, on thermodynamic analysis and insights – Pinch Analysis and recently developed Bridge Analysis, on numerical optimisation - Mathematical Programming, and on hybrid or combined approaches which are based on a combination of heuristics, physical insights and/or numerical optimisation. Optimisation-based approaches could be further divided into deterministic and stochastic (probabilistic) methods. Those systematic approaches (all approaches except pure heuristics) use either sequential (divided into sub-problems) or simultaneous synthesis methods.

Integrated approaches across energy, water and environment systems can accelerate the process of mitigating climate change through urgent action. New scientific advances that extend multiple opportunities in this direction have emanated from the 2nd Latin American, 1st Asia Pacific, 4th South East European and 15th Conferences on Sustainable Development of Energy, Water and Environment Systems as represented in this editorial. The review of recent scientific advances connects the 27 research articles in this special issue with those of other researchers based on eight main themes. The first two themes relate to system flexibility for renewable energy penetration and urban solutions in the energy transition. The foci of these themes include enabling energy system flexibility, climate neutral islands, electrification solutions, optimizing urban energy systems, spatiotemporal modelling of heat demand and smart energy hubs. The next three themes relate to solar energy technologies, hydrokinetic, wind and osmotic innovations as well as bioenergy and combustion modelling. These themes include new advances for predicting and monitoring photovoltaic module performance, thermochemical energy storage for concentrated solar options, artificial intelligence for wind energy, micro-cogeneration, and wastewater utilization. The last three themes relate to batteries and hydrogen energy advances, including sector coupling opportunities, optimizing heat exchangers and networks as well as solutions for redesigning sectors and repurposing post-mining reservoirs for energy storage. There are multi-disciplinary interrelations among these themes and each contribution will support the wide-ranging opportunities for realizing the European Climate Law and any other similar targets around the world for sustaining planetary life-support systems on which sustainable development depends.

Existing studies propose different demand response models and often test them on islands that represent test-beds for new technologies. However, proposed models are often simplified and integrated into energy system models that do not consider the existing limitations of the power grid. This study proposes a novel demand response model based on price differentials on the day-ahead electricity market. The model is implemented in the distribution system that considers all relevant grid constraints. The case study is conducted in an archipelago characterised by a medium-voltage distribution system connected to the mainland grid. The obtained results showed that the implementation of the proposed demand response model caused a 0.13 kV voltage deviation which did not cause voltage issues for the observed distribution system. The breakpoint incentive was achieved for an incentive value of 23% of the day-ahead market, and the demand response was not activated for higher values than the breakpoint incentive. The highest savings amounted to 258.7 V for the scenario with the highest flexibility allowed. The results implicate that implementing the demand response model in the grid would benefit all observed stakeholders in the system.

European Union has definitely identified the priorities towards sustainable and low-carbon energy systems recognizing a key role to islands that have been described as ideal sites to develop and test innovative strategies and solutions that will then boost the transition on the mainland. Nevertheless, the integration of Variable Renewable Energy Sources (vRES) into the electricity grid are already causing technical problems to island grids thus making grid flexibility a key topic. In the past, since power plants were completely manageable while the load was unpredictable, the grid flexibility was supplied by traditional power plants; but now, due to vRES, the variability and unpredictability has moved to the generation side and the opposite shift has happened to flexibility agents. This paper deals with solutions that improve the ability of the grid to cope with vRES unpredictability such as energy storage technologies and all the solutions offered by sector coupling strategies. Particularly, this research focus on solutions that deals with such solutions in the insular contexts. Several solutions have been presented concluding that battery energy systems and pumped hydro energy storage are the most used technologies in islands. As regard sector coupling and Demand Side Management solutions, all the analysed solutions showed relevant results in terms of i) reduction of excess electricity production and ii) increased grid ability of hosting vRES. Nevertheless, some of the current gaps in literature have been pinpointed and future research challenge and opportunities have been suggested.

The increasing amount of municipal solid waste and its consequent disposal has been a crucial issue in promoting a sustainable environment according to the Moroccan Ministry of the Environment. The rate of production of municipal waste was about 5.9 million tons/year, or 0.76 kg/citizen/day in urban areas. The controlled landfill rate was only 32% without energy recovery; the rest is transferred to wild dumps. In this study, alternate scenarios of the municipal solid waste (MSW) management are presented and analyzed. These scenarios aim to evaluate the energy savings and greenhouse gases (GHGs) emissions of four different practices of MSW management (recycling, incineration, landfilling and composting) in Morocco. The study reveals composting as the greatest choice when the energy savings and GHG emission reduction were considered since that organic waste constitutes a large share of the total waste in Morocco (65%); however, recycling of non-organic waste is found to be agreeable under the consideration of GHG emission reduction only. The obtained results will help the authorities involved in MSW management in Morocco to prepare more efficient measures.

In developing countries, national-level institutions are often limited by key transportation energy efficiency indicators. A transportation model based on 40 artificial neural networks was developed to fill this gap. Data on energy efficiency indicators for 28 European countries have been collected to train a model for predicting these indicators using socio-economic variables. A bottom-up approach is then used to compare the predicted data to the total energy consumption. Morocco is used as a case study because of the absence of its energy efficiency indicators. The model's outstanding performance was proved after calculating energy demand at a highly disaggregated level. The model was used to forecast energy consumption up to 2050, considering a variety of alternative hypotheses. Four long-term energy demand scenarios were evaluated: frozen efficiency, implementation of EU legislation, cars electrification, and modal shift. The redistribution of passenger kilometres and tonne-kilometres as a way of rising average occupancy and average load revealed a significantly greater potential for energy savings. Switching from diesel to biofuel for buses and light cars was also examined as a solution to minimize GHG emissions. The developed model supplies decision-making institutions with the necessary tools for identifying critical issues, implementing policies, and redistributing infrastructure.

Tackling climate change can be achieved through local and regional initiatives, such as the Covenant of Mayors, which create energy and climate plans with mitigation measures. Upon the development of energy plans, the mitigation of greenhouse gas emissions (GHG) can be achieved through an individual or joint approach. The research aims to upgrade methods for local and regional energy planning through the choice of mitigation actions and alternative scenarios for the reduction of GHG emissions. This is achieved through optimisation of the selection of mitigation measures in the case of the wider Dubrovnik area in Croatia by choosing the most suitable option for implementation when comparing individual and joint approaches for the planning of the measures. Moreover, the implementation of single and sets of mitigation measures is compared through the total cost abatement curve. The modelled problem represents a non-linear problem as exponential functions and multiplication of variables occurs in the modelled equations. Visualisation of the results is achieved via the total cost abatement curve which ranks measures from the most cost-effective to the least cost-effective. It is shown that with the use of optimisation models, it is possible to find such sets of measures and alternative scenarios, which will, with less financial means, reach a minimal reduction of CO2 emissions by 40% in local and regional energy systems and result in financial savings of three times in the analysed case. In this way, it could be possible to increase the overall implementation of SECAP measures and mitigate the problem of the lack of appropriate financial planning.

Long term planning of energy system’s development becomes closely connected to analysis of day-ahead power markets, market coupling and dynamics of integration of both, renewable energy sources and demand response technologies. In this study a scenario approach with minimization of marginal cost of generated electricity is used to investigate and quantify the influence of investments in generation units for the observed zone and the commitment of units in the surrounding zones. Dispa-SET software was used for modelling of a case study which included eight zones connected in the electricity market. Year 2016 was selected as referent, while future scenarios in 2030 are created with different strategic decision made in each of the zones. Results demonstrate the influence of different strategic pathways in different zones, through electricity generation and levels of storage capacities in the investigated zone and neighbouring zones and cross-border electrical energy flows. If most of the zones are pursuing unambitious strategies (2030a), marginal cost of electricity is double in comparison to the most ambitious case, while moderate approach in the most zones brings the cost reduction of 20%. Ambitious scenario 2030c for all zones results in the least cost of electricity, 30% of the cost in scenario 2030.

The integration of energy, water and environment systems represents important opportunities for addressing the urgent imperative of climate neutrality. The 29 original papers in the virtual special issue of the 14th Conference on Sustainable Development of Energy, Water and Environment Systems exemplify multiple advances in integrated approaches. This editorial provides a review of recent scientific contributions in energy system integration, urban synergies in the energy transition, integration of energy and water systems as well as valorization of waste heat. Advances that relate to sustainable combustion, biomass, and managing emissions provide further perspectives. All seven themes contain new research directions in such areas as solar energy technologies, thermal energy storage, power-to-X technologies, district heating and cooling networks, wastewater treatment plants, water desalination, and salinity gradient technologies. Advanced optimization approaches, big data analytics for cogeneration, thermal management applications, pollution minimization, lignocellulosic biomass, catalysts for alternative fuels as well as carbon capture, storage and utilization are described among other scientific contributions. Across the world, the focus on integration is gaining prominence, especially with the European Union Strategy on Energy System Integration that recognizes the role of a coordinated approach for planning and operating the energy system as a whole. The research advances that are contained in this editorial will support the realization of a coherent approach on the path towards sustaining the life-support systems of the planet and thereby support sustainable development.

Having in mind that European Union (EU) has committed to Paris agreement goal of keeping temperature at less than 1.5 ℃ above preindustrial level, has made decision to reach climate neutrality reached by 2050, and have greenhouse gas (GHG) emissions reduced by 50– 55% by 2030, the issue of avoiding stranded costs should be immediately considered. Since natural gas boilers have life of 20+ years, and infrastructure even more, it is time to start preparing the exit strategy, in order to avoid stranded costs being loaded on consumers and market players.

Power generation sector worldwide accounts for high water withdrawal and consumption due to the hydropower generation and cooling of thermal power plants. Hence, the operation of the power generation sector is constrained by the availability of the water resources, as well as the addition of constrains on water resources used for other purposes, such as irrigation, flood control, water supply, agriculture, etc. The optimal utilization of water resources between the water and energy sector is defined under the term water-energy (or water-power) nexus. This study describes the implementation of hydrological LISFLOOD, Medium-Term Hydrothermal Coordination (MTHC) and Unit Commitment and Dispatch (Dispa-SET UCD) models for detailed analysis of impacts on the SEE regional power system for three different hydrological years. Results were validated based on the available ENTSO-E data for the average hydrological (2015) year. Results show increase in hydropower generation from 53.06 TWh for dry year, to 65.24 and 85.13 TWh for average and wet year, respectively, while the average electricity cost falls from 17.79 EUR/MWh for dry year, to 16.36 and 14.05 EUR/MWh for average and wet year, respectively. This analysis successfully replicates the methodology under the WATERFLEX project, with the novelty in run-of-river hydropower generation calculations in MTHC model.

In order to integrate large shares of variable renewable energy sources, district heating can play an important role. Furthermore, in order to increase the efficiency of district heating systems, interconnecting adjacent system could be socio-economically justified. In order to assess the economic and environmental consequences of the latter, a mixed linear integer optimization model was developed with the endogenous decision on the potential interconnectors. The case study was carried out for the city of Zagreb, Croatia. The results showed that all three studied interconnections are economically viable, while the socio-economic cost was 29.2% lower in the case of the implemented interconnectors, all other capacities being equal. Moreover, the optimal thermal energy storage capacity was found to be equal to 25 and 24 days of average heating demand in two alternative scenarios. Finally, compared to the reference case, the CO2 emissions could be lowered by 15.3%.CO2 savings derive mainly from better utilization of low carbon capacities after interconnecting the systems, as well as from installation of heat pumps and electric boilers.

Energy systems with a high share of variable renewable energy are more vulnerable to sudden changes in the system operation. This is especially emphasized on small systems such as energy systems on geographical islands. Because of these reasons, there is a need for quantifying the risk of energy scenarios of such systems. This paper presents a novel robust risk assessment method under demand uncertainty for energy planning scenarios for the islands. The method uses graph theory for the representation of power system topology. The Poisson distribution is used for calculating the probability of power system element failure. The robust modelling approach is applied by the introduction of auxiliary variables and compared to the deterministic model results. Four energy planning scenarios for Unije island are modelled and subjugated to several power system outages resulting in a risk vector calculated as the product of probability vector and damage matrix. The study also presents a zero-import risk energy planning scenario for Unije island that is achieved for a system of 0.5 MW photovoltaic plant and 3.55 MWh battery storage system.

In each touristic city waste management system has to overcome the impact of visitors. Dubrovnik, famous as popular touristic destination, particularly notices tourists visiting city. Therefore potential impact of waste management in touristic cities, such as Dubrovnik, is presented. The paper includes estimation of yearly waste production by inhabitants and tourists visiting those city. Waste digestion is a method for biogas production. On the basis of the preceding estimation combined-cycle installation generating heat and electricity is proposed. The model combines Brayton cycle with low temperature Kalina model based on Rankine cycle. Literature analysis presents state of the art in this field. The simulation is prepared in Cycle-Tempo. Numerical analyses lead to technical issues, which have to be taken into consideration during waste utilization with such installation. Thus benefits and threats are discussed. The presented analysis assesses the maximal electric gain, which subsequently should consider waste preparation and purification

Energy demand of a transport sector has constantly been increasing in the recent years, consuming one third of the total final energy demand in the European Union (EU) over the last decade. A transition of this sector towards sustainable one is facing many challenges in terms of suitable technology and energy resources. Especially challenging transition is envisaged for heavy-weight, long-range vehicles and airplanes. A detailed literature review was carried out in order to detect the current state of the research on clean transport sector, as well as to point out the gaps in the research. In order to calculate the resources needed for the transition towards completely renewable transport sector, four main alternatives to the current fossil fuel systems were assessed and their potential was quantified, i.e. biofuels, hydrogen, synthetic fuels (electrofuels) and electricity. Results showed that electric modes of transport have the largest benefits and should be the main aim of the transport transition. It was calculated that 72.3% of the transport energy demand on the EU level could be directly electrified by the technology existing today. For the remaining part of the transport sector a significant demand for energy resources exists, i.e. 3069 TWh of additional biomass was needed in the case of biofuels utilization scenario while 2775 TWh of electricity and 925 TWh of heat were needed in the case of renewable electrofuels produced using solid oxide electrolysis scenario.

Efficiently utilizing energy that is currently being wasted can significantly increase energy efficiency of the system, as well as reduce the carbon footprint. In hot climates with large cooling demands, excess waste heat can be utilized via absorption chillers to generate cold. Moreover, cold from liquefied natural gas gasification process can further provide energy source for meeting the cold demand. In order to connect the large sources of waste heat and cold energy with customers demanding the cold, a significant investment in district cooling grid is a necessity. In order to deal with the mentioned issue, an existing energy balance model was complemented with Matlab algorithms in order to model the whole energy system, including the detailed representation of the district cooling grid. Singapore was chosen for a case study and several different scenarios were developed for the year 2050, with the main indicators being total primary energy supply, total CO2 emissions and total socio-economic costs. The most beneficial scenario for the year 2050 had 19.5% lower primary energy demand, 38.4% lower total socio-economic costs and 41.5% lower CO2 emissions compared to the business-as-usual scenario for the year 2050, although significant investment in the district cooling grid was included in the calculations.

District heating and cooling systems represent a valuable infrastructure that can facilitate the integration of various energy sources into urban energy systems. One of those sources is municipal waste. By applying the waste-to-energy concept, landfilled waste amounts can be significantly reduced, and heat, cold and electricity can be produced via combined heat and power plants. This research investigates the possibility of integration of combined heat and power waste incineration plant into the existing gas-based district heating system in the central European city. To secure 365 days of heat demand, the influence of the introduction of a warm district cooling system is simulated, where heat is distributed via the existing heat distribution network to distributed chillers, building sites locations. The results show 33% higher energy-from-waste potential in summer compared to winter, which is an opposite trend to heating demand and compatible with yearly distribution of energy needs for covering cooling demand. Despite the identified compatibility on a seasonal scale, to cover up to 100% of district cooling energy consumption with energy-from-waste, heat storage is needed, due to differences in short-term heat production and demand. This synergy has positive effects on the energy production efficiency and operation of the waste to energy plant and district heating system which results in the highest reduction in fuel consumption as well as in decrease in greenhouse gas emissions. Results of this research can be used for a better understanding of interactions between analysed technologies/systems in the wide range of cities with a continental climate.

Forecasting energy demand for the industrial sector is both interesting and difficult due to the difference in energy demand specific to each industrial sub-sector. For an accurate prediction of the future, Industry Energy Demand model was developed based on multiple linear regression method, using five macroeconomic independent variables. This model was tested by considering Morocco as a study case. Energy demand forecast is based on a bottom-up approach. It is built by piecing together consumed quantity of goods of each sub-sector to give rise to total energy demand. This model produces results comparable to those of the International Energy Agency. Regarding demand forecast, it was found that 8.27 MToe will be needed in 2050 to meet energy demand. It was also found that the adoption of energy efficiency measures allow an energy saving of 1 MToe in 2050. This model was also used to test the impact of variation in import and export on final energy demand. Regarding the potential of the production of biogas from Municipal Solid Waste, it was found that only 36.4% of total Liquefied Petroleum Gas demand could be replaced by biogas.

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.

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.

The EU policy aims towards low carbon economy by establishing a goal of reduction of 93–99% in greenhouse gas emissions in energy sector by 2050. This means a complete energy transition from the fossil fuel based systems to mostly renewable and low-carbon based energy systems. In order to integrate variable renewable energy sources, day-ahead and intraday electricity markets influence, demand – response technologies implementation and fossil fuel powered thermal power plants’ flexibility considerations need to be analysed. Along with the integration of solar photovoltaics, demand – response technologies (power-to-heat and vehicle-to-grid concepts) needed to balance the system, were deployed. In calculations performed on the case study of Croatia in years 2014 and 2030, a moderate introduction of heat storages in Croatian combined heat and power plants, introduction of electric vehicles and flexible operation of power plants enabled the integration of up to 2000 MW installed capacities of solar photovoltaic plants. The main integration criteria, a cumulative critical excess electricity production from solar and wind power, was kept under 5%. Results of this approach are the reduction in full load hours of economically feasible operation for Croatian power plants up to 2000 and combined heat and power plants to up to 3000.

Sustainable energy conversion and management processes increasingly require an integrated approach, especially in the context of addressing the climate crisis. This editorial puts forth related research frontiers based on 28 research articles of the special issue that is dedicated to the 13th Conference on Sustainable Development of Energy, Water and Environment Systems and regional series based on the 1st Latin American and 3rd South East European Conferences. Seven research frontiers are reviewed, the first three of which are (i) sustainable technologies for local energy systems, (ii) energy storage and advances in flexibility and (iii) solar energy penetration across multiple sectors. These research frontiers contain contributions based on renewable energy for wastewater treatment in islands, energy savings across urban built infrastructure, advanced district heating and cooling networks, power-to-gas and hydrogen production technologies, demand response in industrial systems, hybrid thermal energy storage, hybrid solar energy power plants, novel photovoltaic thermal technologies, and improved solar energy dispatchability. The research frontiers continue with (iv) wind, water based energy and the energy-water nexus, (v) effective valorization and upgrading of resources, (vi) combustion processes and better utilization of heat and (vii) carbon capture, storage and utilization. Significant contributions include innovative wind and hydrokinetic turbines, osmotic power technologies, synergetic solutions for water desalination, efficient catalytic pyrolysis, upgrading to reduce particle pollution, co-processing for alternative fuels, combustion characterization, electricity generation from waste heat sources, advances in heat exchangers and heat transfer, oxy-fuel combustion, post-combustion capture, and fly ash recycling for energy storage material. The research frontiers in this editorial provide ample opportunities to support societal transformations in the next decades to sustain planetary life-support systems. - 2019 Elsevier Ltd Scopus

Currently, in the European Union there are two major initiatives that address the issue of sustainable development of the islands. Top-down initiative coming from the Declaration on Clean energy for EU islands and bottom-up Smart Islands initiative. Both initiatives consider islands as living labs that can host innovative pilot projects and lead Europe’s transition into a sustainable and low carbon environment. Following objectives of both initiatives, the Croatian government passes a law on islands that support the development of smart islands. The paper presents a comprehensive review of studies, projects, policy documents and scientific publications related to Smart Islands development in Kvarner archipelago which can be used as a model for implementing new sustainable technology on the islands. It also provides expert recommendations for digitalization in several sectors crucial for the development of islands and an integrated approach to management of island resources.

More variable renewable energy sources and energy efficiency measures create an additional flexibility gap and require a novel energy planning method for sustainable national energy systems. The firstly presented method uses only EnergyPLAN tool in order to decrease the flexibility gap in a national energy system. Generic Optimization program (GenOpt®) is an optimization program for the minimization of a cost function that is evaluated by an external simulation program, such as EnergyPLAN, which was used as the second method in this research. Successful strategies to decrease the flexibility gap are verified on the case of the Serbian national energy system using two methods for its structure design: (1) the iterative method, based on heuristics and manual procedure of using only EnergyPLAN, and (2) the optimization method, based on soft-linking of EnergyPLAN with GenOpt®. The latter method, named EPOPT (EnergyPlan-genOPT), found the solution for the structure of the sustainable national energy system at the total cost of 8190 M€, while the iterative method was only able to find solutions at the cost in the range of 8251–8598 M€ by targeting only one sustainability goal. The advantages of the EPOPT method are its accuracy, user-friendliness and minimal costs, are valuable for planners.

Given that cement is the most widely used material for housing and modern infrastructure needs, this paper analyses the energy efficiency of the cement manufacturing processes for a particular cement plant. The cement industry is one of the largest consumers of carbon-containing primary energy sources and one of the primary polluters of the environment, emitting approximately 5% of global pollution. Energy consumption represents the largest part of the production cost for cement factories and has a significant influence on product prices. Given that it is realised in modern society that infrastructural projects lead to a higher level of economy and sustainability for countries, reducing the production cost in the cement industry is a very important problem. The authors analysed the energy consumption of a particular cement factory in Croatia to determine the minimum energy targets of production and proposed pathways to improve energy efficiency. The Process Integration approach was used in this study. Nevertheless, the features of the cement factory forced the research to update its methodological steps to propose real pathways for a retrofit project with the aim of achieving the optimal minimum temperature difference between process streams. There are various streams, including those that contain solid particles, gas and air streams, and streams, that should be cooled down rapidly; these facts become more complicated by the special construction of the process equipment, which causes heat transfer between some streams to be impossible. The main objective of this paper is to determine the potential of real energy savings and propose a solution for a new concept of heat exchanger network (HEN) that avoids the process traps and provides a feasible retrofit. The maximum heat recovery of that production of a particular type of cement was determined and improved when a HEN was built. The authors conclude that the energy consumption of the cement factory can be reduced by 30%, with an estimated recovery period of 3.4 months. The implementation of this retrofit project helps the plant’s profitability and improves the environmental impact of the cement manufacturing process.

This paper presents a new approach for modeling energy flows in complex energy systems with parallel supply of fresh water and electricity. Such systems consist of renewable energy sources (RES), desalination plant, conventional power plants and the residual brine storage which is used as energy storage. The presented method is treating energy vectors in the system as control variables to provide the optimal solution in terms of the lowest critical excess of electricity production (CEEP) and highest possible share of RES in the supply mix. The optimal solution for supplying the demands for fresh water and electricity is always found within the framework of model constraints which are derived from the physical limitations of the system. The presented method enables the optimization of energy flows for a larger period of time. This increases the role of energy storage when higher integration of RES in the supply mix. The method is tested on a hypothetical case of Jordan for different levels of installed wind and PV capacities, as well as different sizes of the brine storage. Results show that increasing the optimization horizon from one hour to 24 h can reduce the CEEP by 80% and allow the increase of RES in the supply mix by more than 5% without violating the CEEP threshold limit of 5%. The activity of the energy (brine) storage is crucial for achieving this goal.

Intermitted patterns of solar and wind generation cause insecurity in the power system supply since they depend on weather conditions. The aim of this work is to perform linear regression and correlation between solar radiation, wind speed, air temperature and electricity demand of the Dubrovnik region. Gained results could help in system energy planning with a high share of renewable energy sources in the electricity production. All of the data are collected for consecutive three year period, years 2012, 2013 and 2014, in the 10 minute time step. Results of the correlation of each of the parameters individually in between the years show slightly variations between the distributions, providing representative line-ar relation in between the years for all the data, except the wind speed data. Cor-relations are also done between all of the parameters for each year separately, based on the mean monthly values. Result showed good relation with negative correlation between solar radiation and wind speed, as well as good relation with positive correlation between solar radiation and electricity demand. The same correlations are done in the 10 minute time step and including time system delay. The results indicate significant decrease in correlation coefficient value and it is less possible that they can be pronounced with linear regression line. Calculations of the correlation and regression, based on the 10 minute time step for summer and winter period separately, gained slightly better results in relation between parameters than the ones including the whole year data.

The goal of the European Union is to reduce CO2 emissions by 20% till 2020. This objective is transferred to municipalities through the Covenant of Mayors initiative which was established by the European Commission in 2008. In line with this, this paper presents an integration of Sustainable Energy Action Plans on the Croatian island of Korcula. This was developed through a methodology that uses factors, derived from the statistic, that have an influence on the energy consumption. Energy consumption and the Baseline CO2 emissions inventory for municipalities on Korcula in the public sector, households, tertiary sector and road transport are calculated. Total CO2 emissions for listed sectors in baseline 2012 are 42,923 tCO2, and with recommended actions and measures this can be reduced by approx. 22% till 2020. There are planned joint actions, so all municipalities on the island can cooperate together to maximise their limited financial and human capacities. There has been suggested the establishment of action group for actions implementation which will include representatives from municipalities and other stakeholders. Investments for measures in household sector in joint and individual approach was compared and it was concluded that achieving economy of scale with an integrated approach would accelerate their implementation. The integrated approach enables small neighbouring municipalities to develop one strategy and act together towards achieving goals taken by submitting to the Covenant of Mayors.

In the current situation the City of Velika Gorica (the “City”) faces several key issues regarding its thermal energy consumption. The thermal consumption in the City is 197.34 GWh where 20% is supplied by firewood, 2% by electricity, 15 % by fuel oil, 31% natural gas and 32% by the district heating system. In the district heating sector the main issue is the utilization of 14 small and distributed heat plants, each providing heat to a separate and individually disconnected heating grid. Of the fourteen installed plants only one is gas operated bearing 60.76% of the total installed capacity, while the rest use fuel oil resulting in a high level of CO2 emissions as well as the distribution losses due to a high-temperature district heating and an old distribution system. Other issues are the high thermal energy consumption of roughly 200 kWh/m2 in the residential sector and 190 kWh/m2 on average for public buildings. Reduction of costs and CO2 emissions can be reached with a high penetration of renewable sources and decreasing the energy consumption with better insulation. The aim of this paper is to evaluate the integration of solar energy into the district heating system of the City. There are three proposed scenarios for the use of solar energy in the City: (i) producing hot water for a residential-scale use ; (ii) preheating of a district heating plant ; and (iii) thermal energy storage in a solar plant for a district- scale use. In all aforesaid scenarios, the use of the new hybrid photovoltaic-thermal (PVT) collector has been evaluated. The future of the district heating system is concluded to be formed by the connection of the current fourteen small heating grids and operated by two heating plants, one solar plant and one biomass cogeneration plant. The system has been modeled as a low-temperature district heating system. The potential energy covered by solar is 40.4 GWh for hot water demand and 44 GWh for the district heating system.

Jordan is a country faced with several environmental and energy related issues. It is the Worlds' fourth most water deprived country with a water consumption of only 145 m3 per capita annually, less than a third of the established severe water poverty line. Jordan is also a country rich in wind and solar potential but practically no utilization with 99% of the produced electricity coming from imported fossil fuels resulting in high CO2 emissions and a potential security of supply issue. The utilization of reverse osmosis desalination in a combination with brine operated pump storage units and wind and (PV) photovoltaic plants can tackle both issues. The desalination plants can produce the much needed water and act as a flexible demand to increase the penetration of intermittent renewables supported by the brine operated pump storage units. This paper presents six scenarios for the development of the Jordanian energy system until the year 2050. The results have shown that the demonstrated configuration can increase the share of intermittent renewables in the production of electricity up to 76% resulting in a high reduction of fuel consumption, CO2 emissions and costs. These analyses have been performed using the EnergyPLAN advanced energy system analyses tool.

This paper compares district heating systems in Zagreb and Aalborg in order to see their similarities and differences from which conclusions are drawn on how to improve the systems. The method chosen is the comparative analysis. Data is organized and structured so to allow clear and concise comparison. The results of the comparative analysis show that the district heating system in Aalborg is more advanced than the district heating system in Zagreb. This advantage is prominent in aspects of supply, demand, distribution and economic spheres. Some of the possible improvements include lowering specific heat and water losses. Systematic replacements and refurbishments of the old network pipes are key to this. Lowering the supply and return temperatures would enable better renewable energy sources integration. The integration of renewable energy sources in district heating systems is the most important goal that still needs to be achieved.