• Energy Research

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/MWhe 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.

In most countries markets for electricity are divided into wholesale markets on which electricity is traded before the operation hour, and real-time balancing markets to handle the deviations from the wholesale trading. So far, wind power has been sold only on the wholesale market and has been known to increase the need for balancing. This article analyses whether wind turbines in the future should participate in the balancing markets and thereby play a proactive role. The analysis is based on a real-life test of proactive participation of a wind farm in West Denmark. It is found that the wind farm is able to play a proactive role regarding downward regulation and thereby increase profits.

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.

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.

The transition towards renewable energy will operate on different geographical scales. Many of the concrete steps will address the local level; however, these have to align with the broader energy perspective. It is therefore necessary to develop methods to enable cities to assess if their strategies are compatible with the surrounding energy systems. This paper presents a methodology to design Smart Energy Cities within the context of 100% renewable energy at a national level. Cities and municipalities should act locally what concerns local demands, but acknowledge the national context when addressing resources, industry and transport. The method is applied to the case of transitioning the municipality of Aalborg to a 100% renewable Smart Energy System within the context of a Danish and European energy system. The case demonstrates how it is possible to transition to a Smart Energy City that fits within a 100% renewable energy context of Denmark and Europe.

Energy efficiency improvements of buildings is widely recognized as an important part of reaching future sustainable energy systems, as these both reduce the need for energy and improve the efficiency of the heat supply. Finding the correct level of efficiency measures, depends on the type of measure, on the supply system typology as well as on the heat supply cost. As this information is often building-specific, most analyses related to energy efficiency in buildings are carried out in relation to specific renovation projects, while energy plans for larger areas make crude assumptions regarding levels of savings and costs. This article aims at improving the latter, by using a detailed heat atlas in combination with specific marginal energy renovation costs, in a study of Aalborg Municipality in Denmark. In the analysis, all buildings in the municipality are mapped at building level and both the marginal energy efficiency measure costs and the marginal heat supply costs are identified. The buildings are then sorted by their supply type, and marginal costs curves on supply and savings are compared to determine the feasible level of efficiency measures in each building. The results show that both the building type and the supply costs have a large influence on the feasible measures. Furthermore, the results show that a demand reduction of 30% in district heating areas, 35% for buildings with heat pumps and 37% for buildings with oil boilers, for the examined buildings, is socio economically feasible in a Business as Usual 2050 Aalborg Municipality scenario. International Journal of Sustainable Energy Planning and Management, Årg. 25 (2020)

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.