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In 100% renewable energy systems, the requirements for flexibility will be greater than for traditional carbon-based energy systems. New technologies and system setups are needed to provide flexibility for balancing the system. Implementing electricity storages in the energy system could provide parts of the required flexible demand and production, though most of these storage solutions have been shown to have relatively high costs. So-called Carnot batteries have been shown to have a relatively lower cost than traditional batteries, but at a reduced electric efficiency. This paper investigates to what extent large-scale integration of Carnot batteries has a role in the transition to and the operation of 100% renewable energy systems. By implementing Carnot batteries in a 100% renewable energy scenario for Denmark, the energy system effects are identified. The results indicate that the potential economic benefit could be as high as 60.5–66.2 EUR/MWh e discharged, not including costs related to investment as well as operation and maintenance of the Carnot batteries. Thus, large-scale integration of Carnot batteries must perform below this economic threshold to be economic relevant. Existing concepts for stand-alone Carnot batteries are not able to achieve these costs today, therefore solutions for cost reductions should be investigated. • Electricity storages could provide parts of future required system flexibility. • Most of these storage solutions have been shown to have relatively high costs. • Carnot batteries have a relatively lower costs but at reduced electric efficiency. • Large-scale integration of Carnot batteries is tested in a renewable energy system. • Carnot battery concepts should aim for a cost lower than 60.5–66.2 EUR/MWh e. [ABSTRACT FROM AUTHOR]

Future renewable energy systems with high shares of variable renewable energy production must also include technologies and measures to balance these production fluctuations. This could be in the form of electricity storage, energy demand adaptation (also known as demand-side management), or sector coupling. Industry electrification couples electricity and industry sectors by replacing the fossil fuel demand with electricity demands, thus enabling further integration of renewable electricity and transitioning the hard-to-abate energy sector. The effects of electrification on 100% renewable energy systems are rarely investigated. When investigated, one 100% renewable energy system scenario is used, which is often created by the same author, actor or organisation and may result in a narrow view of the possibilities for future energy systems. This study quantifies the role of industry electrification in the context of different 100% renewable energy system scenarios created by different relevant actors, to identify how its role may differ based on the scenario investigated. It is found that direct electrification of industrial process heat demands should be favoured over, e.g., a fuel shift to hydrogen-based process systems, even when these provide more flexibility. • Future renewable energy systems must balance variable production fluctuations. • Industry electrification enables integration of renewable electricity. • Industry electrification is analysed in three renewable energy system scenarios. • Direct electrification should be favoured over hydrogen-based process systems. [ABSTRACT FROM AUTHOR]

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

Abstract: The long-term goal for Danish energy policy is to be free of fossil fuels through the increasing use of renewable energy sources (RES) including fluctuating renewable electricity (FRE). The Danish electricity market is part of the Nordic power exchange, which uses a Marginal Price auction system (MPS) for the day-ahead auctions. The market price is thus equal to the bidding price of the most expensive auction winning unit. In the MPS, the FRE bid at prices of or close to zero resulting in reduced market prices during hours of FRE production. In turn, this reduces the FRE sources’ income from market sales. As more FRE is implemented, this effect will only become greater, thereby reducing the income for FRE producers. Other auction settings could potentially help to reduce this problem. One candidate is the pay-as-bid auction setting (PAB), where winning units are paid their own bidding price. This article investigates the two auction settings, to find whether a change of auction setting would provide a more suitable frame for large shares of FRE. This has been done with two energy system scenarios with different shares of FRE. From the analysis, it is found that MPS is generally better for the FRE sources. The result is, however, very sensitive to the base assumptions used for the calculations. [Copyright &y& Elsevier]

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

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

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

• Focusing on the trade-off problem between industrial excess heat and heat pumps in DH system. • A novel hybrid framework for optimal DH strategy in 100% renewable smart energy systems. • The real energy system of Aalborg, Denmark is employed for technical–economic analysis. • Sector synergies between the DH network, power grid, and gas grid are revealed. • 40% IEH and 20% HP in DH bring Aalborg a balanced near carbon–neutral system with minimum cost. The literature emphasizes the important role of industrial excess heat (IEH) and heat pumps (HP) in future 4th generation district heating and smart energy systems. However, they can potentially have negative or positive effects on the integration of renewable energy sources (RES). It is necessary to find a trade-off between IEH and HP in the transition towards a 100% renewable energy system yet has not been discussed in the literature. This paper presents a comprehensive techno-economic analysis for the optimal district heating (DH) strategy in a 100% renewable energy system. It is conducted based on a novel hybrid methodology framework that couples hourly smart energy system simulation, multi-objective optimization, and multiple-criteria decision making. The optimal share between IEH and HP and associated RES capacity can be determined considering the preferences of policymakers. A scenario for 2050 for Aalborg Municipality in Denmark is used as a case study. Results show that an appropriate mix of IEH and HP, 40% and 20% respectively in the DH supply, should be employed to obtain a balanced near carbon–neutral system with the least cost. Also, the cross-sector effective interactivities between the DH network, power grid, and gas grid are revealed in the smart energy system context. The proposed framework is designed in a general way that can be used in other cities, regions, or countries. [ABSTRACT FROM AUTHOR]