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Today several trends, such as liberalization, decarbonization, renewable energy sources (RES) growth, electrification, and digitalization, are putting more and more pressure on the way the energy sector operates. This has resulted in ongoing transformation into smart grids (SG) and spreading of energy communities (EC), making use of new digital technologies and renewable sources. Within this paper we aimed to compare the conceptual designs of EC energy market topologies with some of their practical applications in Europe. Although previous studies have already examined selected SG topologies, our work provides an umbrella view of all potential designs of energy market configuration in which a community plays an active role. In addition, we follow a pragmatic approach, comparing theory with practice, and showing how the theoretical EC concept is currently embedded in reality. This paper answers two research questions: (1) Which of the theoretical EC network topologies are currently used in practice (2) How and which network topologies of EC have the greatest chance for the implementation in the future projects? To answer these questions, we conduct a literature review together with a comparison analysis of three case studies from the Netherlands and Denmark. This comparison allowed us to formulate some observations and further recommendations on formal structure, communication, and management, which, in our opinion, are significant for organizations planning to set up their first smart EC initiative, especially in countries where the EC concept has not gained popularity yet. • Microgrid connection, centralized or decentralized business models of EC connection are the most common. • The participation of community members is crucial to succeed. • Technology advanced projects must focus on maintaining good relationship with the EC members. • Scrum framework may prove useful in the pursuit of designing tailor-made solutions. • The replication of the projects in another location is rather limited. [ABSTRACT FROM AUTHOR]

Power-to-X technologies are a promising means to achieve Denmark's carbon emission reduction targets. Water electrolysis can potentially generate carbon-neutral fuels if powered with renewable electricity. However, the high variability of renewable sources threatens the Power-to-X plant's cost-efficiency, instead favouring high and constant operation rates. Therefore, a diversified electricity supply is often an option to maximise the load factor of the Power-to-X systems. This paper analyses the impact of using different power sources on the cost of production and the carbon intensity of hydrogen produced by a Power-to-X system. GreenLab Skive, the world's first industrial facility with Power-to-X integrated into an industrial symbiosis network, has been used as a case study. Results show that the wind/PV/grid-connected electrolyser for hydrogen and electricity production can reduce operational costs and emissions, saving 30.6 × 107 kg CO2 and having a Net Present Value twice higher than a grid-connected electrolyser. In addition, the carbon emission coefficient for this configuration is 3.5 × 10−2 kg H2 /kg CO2 against 7.0 g H2 /g CO2 produced by Steam Methane Reforming. A sensitivity analysis detects the optimal capacity ratio between the renewables and the electrolyser. A plateau is reached for carbon emission performances, suggesting a wind/grid-connected electrolyser setup with a wind farm three times the size of the electrolyser. Results demonstrate that hydrogen cost is not competitive yet with the electricity, suggesting an investment cost reduction but can be competitive with the current hydrogen price if the wind capacity is less than three times the electrolyser capacity. [Display omitted] • Green electricity for hydrogen production is key to a profitable investment. • Danish green hydrogen is uncompetitive with today's electricity market price. • By sizing onshore wind properly, green hydrogen is cheaper than blue hydrogen. • Green electricity can reduce the emissions and the cost of hydrogen production. [ABSTRACT FROM AUTHOR]

Smart energy transition includes a widespread deployment of clean energy technologies and intelligent energy management with information and communication technologies (ICTs). In this paper, the smart energy transition is studied from the viewpoint of the technology convergence of renewable energy sources (RESs) and ICTs. Two important, fast-growing and weather-dependent renewable energy generation technologies: wind power and solar PV (photovoltaic) are studied. This paper provides technology convergence analyses of RES and ICT inventions based on international patent data. Digitalisation is changing the whole of society, and according to the results, this transition can also be seen in the studied renewable energy generation technologies. The digitalisation of RES production covers technologies that control, manage and optimise electricity production in different intelligent ways. Differences between wind power and solar PV technologies are found: in the case of wind power, the development from virtually no ICT solutions to partial technology convergence with the ICT sector is straightforward. However, in the case of solar PV, the development of basic technologies has been even faster than the development of the solar PV ICT solutions, which may indicate the immature nature of solar PV technologies during the studied years. The digitalisation of the renewable energy sector poses challenges for RES companies in following and predicting ICT development and opportunities for innovations and collaborations with ICT companies. This conclusion can also be expanded to society and policy levels because focusing on only a narrow field when planning innovation policy instruments can negatively impact the country's competitiveness. • Digitalisation and ICT solutions are impacting on wind power and solar PV technologies. • The prominent RES technologies with ICT solutions control, manage and optimise electricity production. • Wind power patent data shows a straightforward technology convergence trend with ICT. • Basic inventions in solar PV have increased more rapidly than solar PV ICT solutions. • Digitalisation in wind power and solar PV has been driven by the US, Germany, Denmark and Japan. [ABSTRACT FROM AUTHOR]

This paper presents a strategy for achieving a fully decarbonized Danish energy system (including transport and industry) in 2045. The strategy could also be relevant for most countries at a global level. The energy system analysis includes hour-by-hour computer simulations leading to the design of a Smart Energy System with the ability to balance all sectors of the complete energy system. In the analysis, issues such as international shipping and aviation, the sustainable use of biomass, and the exchange of electricity and gas with neighbouring countries are all considered. Moreover, the energy system is coordinated with other sectors to achieve a fully decarbonized society. Finally, the size of the employment impact of investing in decarbonizing the Danish economy is discussed. • A strategy for a fully decarbonized Danish society in 2045. • The inclusion of international shipping and aviation in a country strategy. • A Smart Energy Systems approach modelled by EnergyPLAN. • Detailed calculations of different elements of the strategy in 2030 and 2045. [ABSTRACT FROM AUTHOR]

This paper provides a coherent review of district heating in Denmark, exploring past, present and future perspectives. Danish district heating is known as unique internationally in terms of heat planning strategies, technical solutions and combinations, energy efficiency and sustainability, ownership models and financing, and it has captured the attention of district heating communities and stakeholders worldwide from the early days. Historically, a ban on landfills incentivised waste incineration, and the strategic integration of combined heat and power plants and recycling of waste heat from industry all increased energy efficiency in the energy system. Ultimately, this contributed to the top World Energy Council ranking of the Danish energy system according to the energy trilemma criteria. A cooperative mind-set, welfare state values and the notions of energy efficiency-, availability-, independency- and sustainability were all pivotal for the evolution of the district heating networks throughout Denmark. Other unique features of the Danish district heating sector include large-scale collective heat planning, the mandatory connection, the non-profit principle, the same approximate price for customers irrespective of heat density, and the relatively high average price of district heating. Moreover, district heating knowledge hubs have led to world-wide exports of district heating technologies and know-how. Future challenges for the Danish district heating sector include increasing biomass import dependency, the changing role of combined heat and power plants in the energy system, transitions to non-combustion heat supplies, and competition from individual heat pumps in single-family houses. However, future 'smart' thermal grids will increasingly facilitate sector coupling processes as more renewable energy resources are integrated into the energy system in Denmark and internationally. • Denmark is considered a global forerunner in district heating. • Nationwide collective heat planning and mandatory connection. • District heating penetration rates are among the highest in the world. • Lower carbon dioxide emissions from district heating than from natural gas. • Future challenges vis-à-vis decarbonisation and non-combustion heat supplies. [ABSTRACT FROM AUTHOR]

This paper provides a coherent review of district heating in Denmark, exploring past, present and future perspectives. Danish district heating is known as unique internationally in terms of heat planning strategies, technical solutions and combinations, energy efficiency and sustainability, ownership models and financing, and it has captured the attention of district heating communities and stakeholders worldwide from the early days. Historically, a ban on landfills incentivised waste incineration, and the strategic integration of combined heat and power plants and recycling of waste heat from industry all increased energy efficiency in the energy system. Ultimately, this contributed to the top World Energy Council ranking of the Danish energy system according to the energy trilemma criteria. A cooperative mind-set, welfare state values and the notions of energy efficiency-, availability-, independency- and sustainability were all pivotal for the evolution of the district heating networks throughout Denmark. Other unique features of the Danish district heating sector include large-scale collective heat planning, the mandatory connection, the non-profit principle, the same approximate price for customers irrespective of heat density, and the relatively high average price of district heating. Moreover, district heating knowledge hubs have led to world-wide exports of district heating technologies and know-how. Future challenges for the Danish district heating sector include increasing biomass import dependency, the changing role of combined heat and power plants in the energy system, transitions to non-combustion heat supplies, and competition from individual heat pumps in single-family houses. However, future 'smart' thermal grids will increasingly facilitate sector coupling processes as more renewable energy resources are integrated into the energy system in Denmark and internationally. • Denmark is considered a global forerunner in district heating. • Nationwide collective heat planning and mandatory connection. • District heating penetration rates are among the highest in the world. • Lower carbon dioxide emissions from district heating than from natural gas. • Future challenges vis-à-vis decarbonisation and non-combustion heat supplies. [ABSTRACT FROM AUTHOR]

To reduce the release of CO 2 from traditional energy, wind energy is developed very fast all over the world. This means that more large wind turbines will be installed on land and more environmental impacts will be created from wind turbines. Noise generated from rotating wind turbines in wind farm propagates through a complex flow-field including a varying atmospheric flow and varying wakes created by the wind turbines, which can greatly influence the sound propagation. This paper presents a new multi-fidelity flow-acoustics simulation framework to predict the sound propagation in both near and far fields of wind turbines in wind farm, which has the potential for wind farm application with good accuracy and acceptable computing time (i.e. 8 min with 6 CPUs for the centre frequencies between 20 Hz and 1000 Hz in 1/3 octave bands). The new multi-fidelity flow-acoustics simulation framework (named WindSTAR) consists of a three-dimensional wind farm engineering flow model, an engineering sound source model, and a high-fidelity sound propagation model. To validate the new framework, a comprehensive measurement strategy was designed and performed to measure simultaneously the turbine operations, inflow conditions, wake flow fields and acoustic fields from near to far fields of a 3.9/4.1 MW SGRE wind turbine in Drantum, Denmark. Comparisons between measurements and computations in various flow conditions from stable to unstable atmospheres show good agreements with an averaged absolute difference of 0.8 dBA. Based on its good accuracy and acceptable computational efficiency, the new multi-fidelity framework is able to be used for designing and controlling wind farms. • A new multi-fidelity flow-acoustics simulation framework is developed. • A new 3D engineering wind farm flow model is developed for studying sound propagation. • A comprehensive flow-acoustic measurement is done for a 3.9/4.1 MW wind turbine. • Validations against measurement show good agreement in stable, neutral and unstable atmospheric flows. • The framework has potential for use in wind farm design and control application. [ABSTRACT FROM AUTHOR]

Today, the zero-emission transport system is a public will in megacities. A promising alternative among the countermeasures is to employ Battery Electric Buses (BEB) and Fuel-Cell Buses (FCB) at reasonable prices. This paper addresses Multi-product Charging Stations (MCS) in the selected bus terminals for refilling hydrogen and electricity. The core of MCS is constituted of a pair of Electrolyzer/Fuel Cell working back to back by Proton Exchange Membrane (PEM) technology. The innate flexibility in the operation of such a configuration enables for providing regulating services when the market price is soaring. The multi-criteria programming for the hourly schedule in different weather conditions is investigated using the Crow Search Algorithm. The objective is to enhance the daily profit of charging stations through the optimized multi-products/services selection. Uncertainty in wind speed, market price, and electric vehicles is considered in scenarios. The weightings are decided through the Analytic Hierarchy Process (AHP) and Criteria Importance through Inter-criteria Correlation (CRITIC) methods. The superiority of MC-CSA Stochastic Programming is showcased by simulations on a modified 33-bus IEEE distribution system using DK2 (east Denmark) data under subsidized and liberal markets. Regarding the daily profit outcomes, CRITIC was advantageous on windy days when the market prices vary with wind speed whilst AHP was preferred in low wind hours. The most lucrative operations are achievable when the products are fully accepted by regulating markets, BEBs, and FCBs on windy days. The results indicate that the additional remuneration on green hydrogen leaves a deeper impact rather than subsidies on electricity prices for EVs. • Cogeneration of hydrogen and electricity for city buses is addressed. • Multi-Criteria Crow Search Algorithm is tailored for profit enhancement. • Criteria Importance through Inter-criteria Correlation (CRITIC) method is adopted. • Underlying interdependencies between uncertain parameters are numerically distinguished. • Subsidy on hydrogen as fuel showed more beneficial than on electricity. [ABSTRACT FROM AUTHOR]