District Energy Research Articles

Optimal heat storage in district energy plants with heat pumps and electrolysers

Optimal heat storage in district energy plants with heat pumps and electrolysers

A Multi-Scale method for combined design and dispatch optimization of nuclear hybrid energy systems including storage

Reliable, carbon-free power generation is increasing in importance. Nuclear-renewable hybrid energy systems (NHES) are a potential solution for current generation challenges, but design and dispatch optimization for these systems remains challenging particularly when stochastic effects, long time horizons and nonlinear modeling are needed. This work presents a multi-scale method for combining the design and dispatch optimization problems for nonlinear NHES over long time horizons. Rather than treating the entire horizon as a single optimization problem, a large number of combined optimization problems are solved for shorter samples of the horizon resulting in distributions of optimal capacities for each of the capacities being optimized. The distributions are then aggregated, and the techno-economics of each aggregate is analyzed. The result is a contextual knowledge about the techno-economic tradeoffs for the system rather than a single set of optimal capacities. This method is applied to two NHES of varying complexity. Results indicate that unit capacities for a grid-connected district energy system can be reduced by at least 18.9% by allowing for 3 periods of power import over the course of a 2000 day dispatch. The algorithm is used to solve combined optimization problems with dispatch horizons 112.5 times longer than are solvable directly.

Probabilistic modelling of seasonal energy demand patterns in the transition from natural gas to hydrogen for an urban energy district

The transition to a low-carbon energy system can be depicted as a “great reconfiguration” from a socio-technical perspective that carries the risk of impact shifts. Electrification with the objective of achieving rapidly deep decarbonisation must be accompanied by effective efficiency and flexibility measures. Hydrogen can be a preferred option in the decarbonisation process where electrification of end-uses is difficult or impractical as well as for long-term storage in energy infrastructure characterised by a large penetration of renewable energy sources. Notwithstanding the current uncertainties regarding costs, environmental impact and the inherent difficulties of increasing rapidly supply capacity, hydrogen can represent a solution to be used in multi-energy systems with combined heat and power (CHP), in particular in urban energy districts. In fact, while achieving carbon savings with natural gas fuelled CHP is not possible when low grid carbon intensity factors are present, it may still be possible to use it to provide flexibility services and to reduce emissions further with switch from natural gas to hydrogen. In this paper, a commercially established urban district energy scheme located in Southampton (United Kingdom) is analysed with the goal of exploring potential variations in its energy demand. The study proposes the use of scalable data-driven methods and probabilistic simulation to generate seasonal energy demand patterns representing the potential short-term and long-term evolution of the energy district.

A new solar and wind integrated sodium fast reactor with molten salt to generate multiple useful outputs with hydrogen

The current study proposes the integration of renewable and nuclear energy systems in a hybridized manner to produce multiple useful outputs with synergetic benefits compared to single-generation systems. The proposed integrated energy system is designed to fully meet the power, heating, cooling, freshwater, and transportation requirements of communities and balance the grid, which consists of an offshore wind farm, a floating photovoltaic plant, a sodium-cooled fast nuclear reactor, a molten salt storage system, a steam-based power generation unit, a lithium-bromide absorption chiller, an anion exchange membrane (AEM) electrolyser, a multi-effect desalination unit and a district energy system. The proposed system is also analyzed from the energy and exergy aspects of thermodynamics. Additional modelling and simulations are carried out with time-dependent analysis in a case study for a residential community, which consists of approximately 275,000 of people in California, the United States. The proposed system with 345 MWe, 1,000 MWth sodium-cooled fast nuclear reactor, 100.8 MWe offshore wind farm and 100 MWp floating PV plant is analyzed with changing parameters throughout the year. Furthermore, the overall system is found to be fully sufficient to meet 1,551.4 GWh of non-thermal electricity load, 820.3 GWh of cooling load, and 2,324.8 GWh of heating load. Moreover, to exploit the excess energy and recover the waste energy, to produce more than the triple amount of the freshwater requirement of the community with 39,575,634 tonnes of fresh water and exceeds the transportation fuel requirement of the community with a total of 28,713 tonnes of hydrogen. The highest monthly average energy efficiency is found for the month of December as 72.54%. On the other hand, the highest monthly average exergy efficiency is found for the month of October as 61.11%. The average energy and exergy efficiencies for the overall system are found 63.36% and 52.42%, respectively.

A review of the different power system architecture at the district level and its analysis

The new power system at the station level is the phased product of the large-scale and high-proportion penetration development of wind and solar new energy. The source network load storage system with the station area as the smallest adjustable unit is constructed by using energy storage +. Different from the traditional substation area system, the architecture of the new power system at the substation area level becomes extremely complex due to the change of access terminal attributes, interaction relationship and various business types. In order to systematically describe the new power system architecture at the station district level, this paper first combs and summarizes the relevant literature at home and abroad, and summarizes the literature related to the current substation District, wind and new energy access and energy storage system regulation. Secondly, from the perspectives of demand differences, common functional requirements and non functional requirements, the requirements of station area level new power system under different application scenarios are classified and analyzed in detail. Then, a new power system for different scenarios is designed, which is divided into local equipment layer, edge control layer, station management layer and centralized control layer from bottom to top, and the functions of each layer are described in detail. Taking Zhangjiajie scenery storage and charging comprehensive energy demonstration project as an example, this paper expounds the ways of terminal data access, transmission and visualization under the framework of Taiwan district level new power system, so as to provide reference for the networking of other similar projects. Finally, the research contents of this paper are summarized, and the contents that need further research in the future are prospected.

An Exploratory Study on Swedish Stakeholders’ Experiences with Positive Energy Districts

Positive energy district (PED) is a novel idea aimed to have an annual surplus of renewable energy and net zero greenhouse gas emissions within an area. However, it is still an ambiguous concept, which might be due to the complexity of city district projects with interconnected infrastructures and numerous stakeholders involved. This study discusses various aspects of PED implementation and presents practitioners’ experiences with the PED concept, challenges, and facilitators they have faced with real projects. The study is based on interviews with ten Swedish professionals. The major challenges reported for PED implementation were local energy production and energy flexibility, sub-optimization, legislation, suitable system boundaries, and involvement of stakeholders. Most of the interviewees mentioned improved collaboration, integrated innovative technology, political support, and climate change mitigation goals as important facilitators. The interviewees highlighted the importance of a local perspective and considered each city’s preconditions when developing a PED project. The study emphasizes that to facilitate PED implementation and replication in cities, more knowledge and clarity is required about PED such as on the definition and system boundaries.

Quantification of overlapping heating and cooling demand for the feasibility assessment of bi-directional systems over Europe

With warmer climate conditions, the growing need to cool down building environment in Europe calls for efficient solutions to solve the heating and cooling demand altogether. To meet such requirement, the bi-directional fifth generation district heating and cooling (5GDHC) system has been proposed in recent years, while having the capability of integrating the renewable and waste energy sources. The overlapping heating and cooling demand, or referred to as the simultaneous demand, is proved as the key pre-requisite to guide the application of 5GDHC through several case studies. However, how large is this overlapping part in the practical building stock and where are the feasible areas for 5GDHC remain unclear. To close the gap, this study assesses the quantities and geographical distributions of overlapping heating and cooling demand across Europe in EU 27, UK, and EFTA countries. Using GIS-based methods and data sources, the study region is split into 28 million hectare-sized units where the overlapping demand is specifically calculated. Moreover, the possible future changes to the heating and cooling demand alone brought by warmer climate, building renovations, and increased cooling area were investigated. The results from reference condition at year 2016 reveal that less than 0.1% of the building stock has DOC larger than 0.3, which is the threshold for 5GDHC being energy efficient. These potential areas are primarily found in city centres involving cooling demands from commercial and industrial processes. In the future scenarios of year 2050, while a better energy performance of buildings and warmer climate may decrease the heating and increase the cooling demand, the overlapping part is only slightly increased by around 5%. Accordingly, around 2500 ha-sized units from the entire study region are found to meet the DOC limit required by the 5GDHC while having large enough demand density to support district energy systems. The presented works geographically identified the potential areas for 5GDHC and can be extended with regional details to serve as the connection between top-level planning and bottom-level case studies.

Renewable smart energy network: A thermoeconomic comparison between conventional lithium-ion batteries and reversible solid oxide fuel cells

Smart energy networks including renewables and energy storage systems are a promising technology for improving the sustainability of residential districts and private mobility. In this work, a smart energy network is analyzed, based on photovoltaic panels, electric energy storage systems, heat pumps and electric vehicles. The system consists of a fully electric residential district, where air-to-air heat pumps are used for space heating and cooling and air-to-water heat pumps provide domestic hot water; a photovoltaic field meets the power load of the residential district, including charging stations for electric vehicles. A district electric energy storage system is included for balancing power supply and demand: two storage technologies are considered and compared in this work: a lithium-ion battery and a reversible solid oxide fuel cell. These systems are modelled and dynamically simulated in Transient Systems Simulation Program (TRNSYS) 18. A case study is discussed, where the proposed systems exhibit promising results in terms of primary energy saving: for example, the renewable energy matches almost 74–77% of the district primary energy demand for the analyzed smart energy districts. Moreover, both the proposed systems achieve very profitable results with a payback period of 3.5–4.4 years. Both the analyzed layouts achieve very similar results.

Solar cadastre for assessment of near-zero energy districts

The building sector is responsible for approximately 40% of the total energy consumption in Europe, with most of it allocated to space heating. Additionally, a continuous increase has been observed in conventional energy prices, as well as a dependency of energy supply on geopolitical stability. Building energy independence and net zero energy buildings and districts are presented as a way to overcome these issues, with the addition of on-site renewable energy, and specifically solar energy, exploitation. The intention to utilise solar energy on-site creates the need for solar mapping in urban areas. A dynamic solar potential estimation is essential for the proper dimensioning of solar systems, and it is conducted in this study via the Energy3D software. A typical urban neighbourhood in Thessaloniki Greece is selected and a simplified version of a Solar Cadastre for the area is produced. The annual solar potential of the selected buildings is calculated and analysed, and the parameters affecting it are presented. Additionally, an estimation regarding the electricity production of typical photovoltaic panels installed on the building surfaces is conducted. The calculations highlight the importance of vertical facades as building integrated photovoltaic (BIPV) systems carriers.

Energy citizenship. Tools and technologies to enable transition in districts

Responses to the current energy crisis and to action against climate change have produced a wide variety of experimentations. Positive Energy Districts (PEDs) and Energy Communities (EC) are spreading as aggregators of enabling technologies, but the knowledge and skills required to plan, implement and monitor them still need to be developed. Technology alone is not enough to facilitate knowledge sharing and the experimentation and co-creation of solutions. The paper focuses on methods and tools that allow to support the creation of “energy citizens” through considerations developed in project H2020 GRETA (Green Energy Transition Actions) and in COST Action ‘PED-EU-NET’.

A combined workflow to generate citywide building energy demand profiles from low-level datasets

Urban building energy models provide an efficient way to estimate the district's energy demand and have been vigorously developed over the years. However, due to the lack of crucial information about building's physical descriptions, existing datasets cannot always meet the significant data demand for modeling. In addition, it is challenging to balance simulation time while ensuring simulation accuracy. Therefore, in order to solve the above difficulties, this paper makes some improvements and optimizations based on reduced-order building modeling and experience-based archetypes and presents a novel two-step approach combining bottom-up and top-down methods. A case study in a suburban district in Germany was chosen as a sample test case to demonstrate these workflow automation tools. The proposed workflow achieved a mean absolute percentage error of less than 2% for citywide energy demand prediction using low-level public data, compared to an error of 15% in the scenario without public data. The results indicate that although there was a lack of specific input data, the presented workflow was capable of obtaining accurate results with reduced computation time. The presented methodology offers an efficient way to establish urban building energy models using low-level datasets and provide relatively accurate results on a district level.

Toward Positive Energy Districts by Urban–Industrial Energy Exchange

The concept of Positive Energy Districts (PEDs) has emerged as a promising approach to achieving sustainable urban development. PEDs aim to balance the energy demand and supply within a district while reducing the carbon footprint and promoting renewable energy sources. Urban–Industrial Symbiosis (UIS) is another approach that involves the exchange of energy and resources between industrial processes and nearby urban areas to increase efficiency and reduce waste. Combining the concepts of PED and UIS can create self-sufficient, sustainable, and resilient districts. As the analysis and implementation of such systems are barely studied in North America, this research study was structured to fill the gap by evaluating the financial and environmental advantages of this combination. This study proposes a methodology to design a heat transmission system; then, it is applied to the case of a paper-making factory and a multifunctional heritage building in Montreal, Canada. The results show that the building’s new heating system can generate sufficient heat while emitting near-zero direct emissions. Overall, this paper argues that combining the concepts of PED and UIS can lead to a more sustainable and resilient urban area, and provides a roadmap for achieving this goal.

ChatGPT for Fast Learning of Positive Energy District (PED): A Trial Testing and Comparison with Expert Discussion Results

Positive energy districts (PEDs) are urban areas which seek to take an integral approach to climate neutrality by including technological, spatial, regulatory, financial, legal, social, and economic perspectives. It is still a new concept and approach for many stakeholders. ChatGPT, a generative pre-trained transformer, is an advanced artificial intelligence (AI) chatbot based on a complex network structure and trained by the company OpenAI. It has the potential for the fast learning of PED. This paper reports a trial test in which ChatGPT is used to provide written formulations of PEDs within three frameworks: challenge, impact, and communication and dissemination. The results are compared with the formulations derived from over 80 PED experts who took part in a two-day workshop discussing many aspects of PED research and development. The proposed methodology involves querying ChatGPT with specific questions and recording its responses. Subsequently, expert opinions on the same questions are provided to ChatGPT, aiming to elicit a comparison between the two sources of information. This approach enables an evaluation of ChatGPT’s answers in relation to the insights shared by domain experts. By juxtaposing the outputs, a comprehensive assessment can be made regarding the reliability, accuracy, and alignment of ChatGPT’s responses with expert viewpoints. It is found that ChatGPT can be a useful tool for the rapid formulation of basic information about PEDs that could be used for its wider dissemination amongst the general public. The model is also noted as having a number of limitations, such as providing pre-set single answers, a sensitivity to the phrasing of questions, a tendency to repeat non-important (or general) information, and an inability to assess inputs negatively or provide diverse answers to context-based questions. Its answers were not always based on up-to-date information. Other limitations and some of the ethical–social issues related to the use of ChatGPT are also discussed. This study not only validated the possibility of using ChatGPT to rapid study PEDs but also trained ChatGPT by feeding back the experts’ discussion into the tool. It is recommended that ChatGPT can be involved in real-time PED meetings or workshops so that it can be trained both iteratively and dynamically.

Distribution grid electrical performance and emission analysis of combined cooling, heating and power (CCHP)-photovoltaic (PV)-based data center and residential customers

As the number of data centers is increasing worldwide, there are concerns about their growing electricity demand on power grids and its impact on the environment. These concerns can be mitigated at the urban scale by utilizing the waste heat generated by data centers and multi-energy hub integration. Using Combined Cooling, Heating, and Power (CCHP) and Photovoltaic (PV) systems within a data center, in combination with district energy network connections, can create energy interactions with residential customers in a multi-energy hub. However, connecting large energy consumers and distributed energy systems to the electrical distribution grid presents challenges due to the conventional design of the power grid with unidirectional electricity flow. There is a lack of understanding about the grid impact of data centers with multi-energy systems regarding electrical performance parameters, energy demand, and emissions. To address these open issues, we developed an hourly energy interaction model that includes a CCHP-PV-based data center and residential customers. In addition, the CCHP-PV-based data center was operated with a cost-optimized energy scheduling. We conducted six case studies to distinguish the specific effects of CCHP, PV, and district energy network connections. The model takes into account hourly outdoor temperatures, energy prices, and varying energy demands to capture the seasonal impact on electrical performance parameters and energy results. From an energy and environmental perspective, CCHP-PV systems can eliminate the data center's electricity demand from the grid, reduce residential energy demand, and decrease carbon dioxide equivalent emissions. This cleaner production and energy exchange further support the United Nations Sustainable Development goals. The experimental results showed a 43% reduction in power loss in the distribution grid and helped the data center's main electrical bus and residential bus against the voltage drop phenomenon. The CCHP-PV-based data center with district heating and cooling connection reduced the peak hour electricity demand on the grid by 39% and annual electricity consumption from the grid by 66%. Furthermore, Greenhouse Gas Protocols (GHG) Scope-2 emissions associated with the data center's grid electricity consumption and only residential electricity consumption were reduced by 77% and 36%, respectively.

Energy transition for the rich and energy poverty for the rest? Mapping and explaining district heating transition, energy poverty, and vulnerability in Czechia

This paper considers the planned transformation of the district heating sector as an opportunity to protect households from energy poverty, while also acknowledging the potential for increased susceptibility. We aim to contribute to energy vulnerability research through a two/phased sequential explanatory research design, which is uncommon in energy poverty research. In the first stage, we develop an index to reveal the detailed socio-spatial distribution of urban energy vulnerability in Czechia. This index can be used as a primary tool for targeted regional and local policies. In the second stage, we confirm the validity and disaggregation of the index through local research. In addition, this process uncovers vulnerabilities not captured by the index or that add meaning and depth to known vulnerability factors. We identify multiple pathways of energy vulnerability stemming from socioeconomic and material-technical factors, as well as combinations thereof. Our research shows that urban energy vulnerability is rooted at different levels, ranging from the household to the state, and is influenced both by past deregulation/liberalisation efforts and rising energy prices, which can jeopardize planned projects. Our analysis highlights the crucial role of district heating systems in urban energy vulnerability, their socio-economic fragility, and their inherently political nature.

Solar Photovoltaics in District Heating and Cooling Sector: An Overview

With the prevalent energy scenario and climate changes, decarbonising energy sector has become the need of the hour. An environmentally friendly way is the utilisation of solar energy, which mainly involves the deployment of photovoltaic (PV) panels and/or solar thermal collectors. Unlike electricity generation, the application of photovoltaics in the district heating & cooling (DHC) sector is relatively new. Also, this energy route is not fully explored by scientific community. This paper aims to provide an overview of the photovoltaic application in district heating & cooling sector. At first, the utilisation of solar energy in the DHC sector is briefly described. Then relevant literature in PVDHC is reviewed. It was understood that different topologies are in place for solar energy integration in the DHC system. These topologies vary in terms of the chosen technology, energy storage, system configuration (centralized/distributed) and components. It was found that the research database on the studied topic needs enhancement, with a special focus on PV cooling. From the literature survey, it is deduced that solar PV could play a significant role in future DHC systems due to the possible combination with other energy sources or electric grid or storage technology. Based on the SWOT analysis, it is concluded that there is an enormous opportunity for PV integration in the DHC sector. However, adequate techno-economic support is required to overcome threats and weaknesses. This study is expected to be beneficial to policymakers, researchers and other stakeholders in district energy market.

Towards Positive Energy Districts: Energy Renovation of a Mediterranean District and Activation of Energy Flexibility

The paper presents the analysis of energy retrofitting, integration of renewable energy and activation of energy flexibility in a cluster of buildings in the surroundings of a port on the Mediterranean Sea in Southern Italy, with the aim of checking the potential for it to achieve the status of positive energy district (PED). The objective of this study is to improve the contemporaneity between local energy generation and energy demand and reduce CO2eq emissions by considering signals that reflect the environmental variability of the electricity grid, through flexibility solutions applied to the HVAC system. The proposed scenarios are based on the dynamic simulation of the district and analyze the effect of actions that activate the energy flexibility of buildings through advanced control strategies of the air conditioning system. The results show that the joint action of energy efficiency strategies, integration of solar energy and energy flexibility improves the environmental sustainability of the district and the balance of energy flows. Specifically, the activation of energy flexibility contributes to a 10% reduction in operational CO2eq emissions and increases in self-consumption of energy per year. The operational emissions of the district vary from the base value of 33.37 tons CO2eq/y to 19.52 tons CO2eq/y in the scenario based on the integration of solar energy systems and energy efficiency measures, and to 17.39 tons CO2eq/y when also the demand-side energy flexibility is activated.

A Quantitative Positive Energy District Definition with Contextual Targets

This paper presents the goals and components of a quantitative energy balance assessment framework to define Positive Energy Districts (PEDs) flexibly in three important contexts: the context of the district’s density and local renewable energy supply (RES) potential, the context of a district’s location and induced mobility, and the context of the district’s future environment and its decarbonized energy demand or supply. It starts by introducing the practical goals of this definition approach: achievable, yet sufficiently ambitious, to be inline with Paris 2050 for most urban and rural Austrian district typologies. It goes on to identify the main design parts of the definition—system boundaries, balancing weights, and balance targets—and argues how they can be linked to the definition goals in detail. In particular, we specify three levels of system boundaries and argue their individual necessity: operation, mobility, and embodied energy and emissions. It argues that all three pillars of PEDs, energy efficiency, onsite renewables, and energy flexibility, can be assessed with the single metric of a primary energy balance when using carefully designed, time-dependent conversion factors. Finally, it is discussed how balance targets can be interpreted as information and requirements from the surrounding energy system, which we identify as a “context factor”. Three examples of such context factors, each corresponding to the balance target of one of the previously defined system boundaries, operation, mobility, and embodied emissions, are presented: density (as a context for operation), sectoral energy balances and location (as a context for mobility), and an outlook on personal emission budgets (as a context for embodied emissions). Finally, the proposed definition framework is applied to seven distinct district typologies in Austria and discussed in terms of its design goals.

GIS for the Potential Application of Renewable Energy in Buildings towards Net Zero: A Perspective

Environmental, economic, and social activities involve inherent spatial dimensions. The geospatial information system (GIS), a platform containing principles, methods, and tools to link, create, visualize, analyze, and model artificial activities and environment, provides the possibility to develop sustainability in the building sector. With globally political collaborations across governments, the demands to manage and visualize sustainable data (e.g., building energy and environment with geospatial reference) and implement more rigorous building modelling are increasing. A systematic mapping at multiple scales will help urban engineers, architectural engineers, policymakers, and energy planners identify emission hotspots, locate spatial resources, restructure district energy mix, and achieve net zero energy targets. To achieve net zero energy goals, it is crucial to minimize energy consumption, improve energy efficiency, and most importantly, apply renewable energy in buildings. However, these processes imply many aspects and challenges, regarding e.g., data availability, scalability, integrability, and a lack of clear and applicable frameworks. In this conceptional perspective paper, we aim to explore the potential of applying and installing renewable energy in net zero energy buildings using the GIS. More specifically, the described virtual framework will effectively support policy- and decision-makers in optimizing the energy structure, reducing building emissions, and applying renewable energy technologies. We also present challenges, limitations, and future directions for real practice.

How to develop fifth-generation district heating and cooling in Sweden? Application review and best practices proposed by middle agents

Sweden has an ambitious plan to fully decarbonise district heating by 2030 and to contribute with negative emissions of greenhouse gases in 2050. The vagaries of the energy market associated with climate, political, and social changes entail cross-sectoral integration that can fulfill these national targets. Fifth-generation district heating and cooling (5GDHC) is a relatively new concept of district energy systems that features a simultaneous supply of heating and cooling using power-to-heat technologies. This paper presents best practices for developing 5GDHC systems in Sweden to reach a consensus view on these systems among all stakeholders. A mixed-method combining best practice and roadmapping workshops has been used to disseminate mixed knowledge and experience from middle agents representing industry professionals and practitioners. Four successful implementations of 5GDHC systems are demonstrated and the important learned lessons are shared. The best practices are outlined for system planning, system modeling and simulation, prevailing business models for energy communities, and system monitoring. A roadmap from the middle agents’ point of view is composed and can be utilised to establish industry standards and common regulatory frameworks.