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Large-scale solar district heating has increased fast recently and is a commercial industry in Denmark with over 100 systems. Pit stores with high solar fraction exist in several of these systems. Some economic factors in Sweden are not as good as in Denmark. However, recent events have forced up the price of biomass in Sweden and other competing uses for the forest resource point to greater competition and thus higher prices, resulting in better viability for solar. The project has used geographic and geological data from e.g. SGU to identify which areas in Sweden that are potentially suitable for pit stores. The results from the screening process show that the vast majority of district heating areas have potentially suitable areas for pit storage within a reasonable distance from the network. Only 86 district heating areas do not. As there is no reliable data for the whole country for ground water level and flow, both important factors for economic viability, the results are optimistic. As to be expected, the results show large variations over the country, but in general there are more suitable areas in the south than north. The project also estimated how much heat solar and pit storage systems could potentially deliver to the district heating areas with suitable areas. If all of these identified district heating areas installed solar and pit storage systems covering 20% of their demand, 15% of Sweden’s total district heating demand would be supplied by solar. If all networks with potential areas for pit storage installed systems covering 40% of the local demand, the equivalent figure is 36%. Pre-feasibility studies for Råneå, Härnösand and Söderhamn show that the heat cost for solar heating systems is slightly higher than the current production heat cost in these networks, given the current interest rate. As the heat cost for solar is mostly dependent on the investment cost, it varies over time in principle only with the interest rate. A lower interest rate or small annual increases in fuel costs would make the studied solar heating systems economically viable. Costs, as for many other technologies, are lower for larger systems. Integration of a heat pump in the system is cost effective if the site of the pit store is in the periphery of the network and the district heating system has exhaust gas condensation. In practice there are many additional factors that can hinder building a pit store in the sites identified as suitable in the screening. The results of the screening are theoretical and are based on the assumption that none of these negative factors exist. Detailed on-site geological measurements are needed if one wants to take the next step in actually building a pit store.

This paper is the second of three accounts which describes a Swedish study aiming to derive a first order assessment of the national potential for large-scale solar thermal heat production with pit thermal energy storage’s (PTES) connected to existing district heating systems (DHS). Whereas the first paper presented project objectives, outset parameters, and an updated Swedish district heating database – and the third is planned to report on the final project results and conclusions – this paper focuses on the assembled study data and the associated selection criteria applied to these data categories under the objective to distinguish suitable (and non-suitable) land areas within cost-efficient heat transmission distances from the existing DHS. The approach centres around a principal spatial analysis with superposition of study data and elimination of non-suitable land areas according to the used selections criteria but also entails a wide periphery of related activities, such as literature reviews, gathering of technology preferences, meetings with sector experts, data management etc. Apart from technical specifications for solar heat production and seasonal storage, key data categories for the spatial analysis consist of geological data (e.g. soil types, soil depth, bedrock etc.), hydrological data (lakes, rivers, wells, soil moisture, ground water levels etc.), geographical data (elevation, built-up areas, administrative units etc.), and thematic data (energy statistics, building heat demands, district heat deliveries etc.). Selection criteria for the relevant data categories have been definediteratively during e.g. expert consultancy, for example minimum soil depth, preferred soil types, maximum feasible transmission distance to existing DHS etc. By application of the selection criteria, raw input data are converted to processed data extracts to be used in the final analysis. Study data categories are illustrated and summarised (raw and processed) together with a listing and discussion of the used selection criteria.

Sweden was among the first countries to install solar thermal plants for district heating (DH) as early as in 1970s. However, in recent years, the focus on solar DH installations has shifted primarily to Denmark and Germany, with only one recent installation reported in Sweden. Nonetheless, due to changes in the overall heating market, the use of large-scale storage (both with and without solar heat) is becoming increasingly important. Despite significant advancements in adopting DH systems, the combination of solar DH with PTES is not well studied from Swedish context. The economic and geological prerequisites for the deployment of PTES remain largely unexplored. This paper explores the integration of large-scale solar thermal systems into DH networks in Sweden, particularly highlighting the feasibility and potential of pit thermal energy storage (PTES) systems. Through findings from a national project, this paper assesses the techno-economic-geological viability of PTES alongside solar thermal collectors, providing insights into the project’s methodological approach and initial findings.

The COVID-19 outbreak is exacerbating uncertainty in energy demand. This chapter aims to investigate the impact of the confined measures due to COVID-19 outbreak on energy demand of a building mix in a district. Three levels of confinement for occupant schedules are proposed based on a new district design in Sweden. The Urban Modeling Interface tool is applied to simulate the energy performance of the building mix. The boundary conditions and input parameters are set up according to the Swedish building standards and statistics. The district is at early design stage, which includes a mix of building functions, i.e., residential buildings, offices, schools, and retail shops. By comparing with the base case (normal life without confinement measures), the average delivered electricity demand of the entire district increases in a range of 14.3–18.7% under the three confinement scenarios. However, the mean system energy demands (sum of heating, cooling, and domestic hot water) decrease in a range of 7.1–12.0%. These two variation nearly cancel each other out, leaving the total energy demand almost unaffected. The result also shows that the delivered electricity demands in all cases have a relatively smooth variation across a year, while the system energy demands follow the principle trends for all the cases, which have peak demands in winter and much lower demands in transit seasons and summer. This chapter represents a first step in the understanding of the energy performance for community buildings when they confront with this kind of shock. © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023.

This document is the final report for activity B2, “Design guidelines” of the IEA SHC Task 65, “Solar Cooling for the Sunbelt regions”. It presents the collection of design and system integration guidelines for solar cooling projects.For this purpose, a comprehensive questionnaire was created that details various solar cooling components,design, sizing, and other sub-systems, such as heat rejection units and cold distribution systems. Data from 10case studies show the performance of solar cooling systems with varying boundary conditions. Additionally, threedifferent case studies, each with their own scope and unique characteristics, are discussed. The summary is asfollows:

• Industrial cooling offers significant opportunities for solar thermal cooling applications. Such systems canachieve a high solar fraction and thus significantly reduce CO2 emissions compared to conventionalelectricity-powered chillers.

• The integration of solar PV with vapor compression chillers is an emerging solution for the decarbonizationof cooling systems. A comparative analysis considering different load and weather profiles suggests thatsolar PV cooling can result in a lower levelized cost of cooling compared to solar thermal.

• Hybrid chillers emphasize the potential of combining electrical and thermal chillers. Both simulation andpractical results indicate a significant reduction in electricity consumption when using the topping cycle ofan adsorption chiller.In summary, these case studies highlight the transformative potential of cooling solutions. As technology advancesand policies evolve, the adoption of such systems will play a critical role in shaping a greener and more energyefficient cooling future.

Heating accounts for approximately 50 % of all final energy consumption worldwide. To decarbonise heating, renewable energy sources must be employed. To account for intermittency of renewable energy sources and provide operational flexibility, low cost and versatile thermal energy storage unit integrated systems are required. Rock-based high temperature thermal energy storage (up to 600 °C) integrated with high temperature solar thermal collectors provide a solution to reduce natural gas consumptions in steam boilers for medium temperature (100 °C–250 °C) industrial processes. This study develops and validates a two-dimensional model of an existing vertical flow 1 MWh high temperature thermal storage unit using experimental data. A parametric study is performed to evaluate the key design parameters and their effect on the temperature profile and charge efficiency. The charge efficiency was found to be in the range of 77–94 %. This pilot scale model is upscaled in the numerical model to an industrial level 330 MWh storage where the output temperature and flowrate are presented for a constant power output, taking into consideration the residual input heat from the solar thermal collectors.

“Heat is half” of the global final energy consumption, and the decarbonization of the heating sector is critical to achieving climate goals. This thesis employs a system modelling approach to evaluate renewable heating systems. The overarching goal is to reduce fossil fuel reliance by integrating renewable energy technologies, such as solar thermal, photovoltaics, photovoltaic thermal, heat pump, and thermal energy storage in different system concepts. Two primary sectors are addressed: buildings, with a focus on utilizing solar collectors and heat pumps for heating systems in multifamily houses by recovery of waste heat; and industries, utilizing solar collectors for steam generation below 200 °C. The work is centred around five primary research questions, addressing the technical and economic feasibility of the mentioned technologies and their roles in decarbonization.

Two system arrangements were simulated to address the heating demands of buildings: a) Centralized heat pump that utilizes ventilation air as a heat source, serving three multifamily buildings, and b) A fifth generation district heating system that utilizes industrial waste heat as its source. The techno-economic performance of these systems was evaluated. The results suggest that the economic viability of such arrangements largely depends on critical factors that include the costs of heat pump sub-stations, prevailing electricity prices, and the cost of waste heat. Incorporating solar air heating collectors and optimizing flow controls enhance both component and system energy efficiency. Moreover, integrating photovoltaic systems, up to a specific capacity, is advantageous as it offers reductions in heating costs.

For industrial steam generation, the importance of the solar fraction in technological comparisons is highlighted. Parabolic trough collector and heat pump for steam generation are compared for 34 locations in the European Union, using solar fraction as an indicator. The results highlight the economic competitiveness of both technologies for a wide range of boundary conditions. However, heating costs from solar thermal collectors increase at higher solar fractions, primarily due to the storage costs. This trend sets an economic limit on the maximum feasible solar fraction. As a result, hybrid systems combining solar thermal collectors with steam heat pumps offer a promising combination to achieve a high renewable fraction for industrial applications.

Concerns about CO₂ emissions from the electricity grid, and its reliability in many countries, necessitate the exploration of alternative system concepts to meet a higher fraction of heating demand. One such novel energy system combines a parabolic trough collector, photovoltaic, and thermal energy storage (using water and sand as storage media) to reach a combined solar fraction of 90 %, while remaining cost-competitive with fossil fuels. The techno-economic performance of solar thermal collectors is system dependent, largely influenced by their integration within industrial systems. Two novel indicators are introduced to quantify the integration incompatibilities, offering insights into the dynamics for specific integration point. Using this method for a case study resulted in an optimized configuration, improving the overall system performance.

Collectively, the results are expected to be leveraged by relevant stakeholders to advance the cause of heating decarbonization in buildings and industries.

A 5th generation district heating (5GDH) system consists of a low-temperature network used as a heat source for de-centralized heat pumps to serve heating demand. Until now, there is a lack of studies looking into the economic aspect of implementing the 5GDH concept. The performance characteristics, system dynamics, and economic feasibility of the 5GDH system are insufficiently investigated in cold climates. This paper aims to bridge the research gap by performing the techno-economic analysis of a 5GDH system using a case study based in Tallinn, Estonia. A detailed thermo-hydraulic simulation model is constructed in TRNSYS and Fluidit Heat. In addition, the uncertainty and sensitivities on the economic performance are analysed using Monte Carlo method implemented in Python. The study further analyses the effectiveness of using solar power technologies in reducing the cost of heating. For designed boundary conditions, the system can deliver heat at levelised cost of heating (LCOH) of 80 €/MWh. Integration of photovoltaic up to a limited capacity results in 1 % reduction when compared to the base case LCOH. The economic benefit of photovoltaic thermal is lower compared to photovoltaic. This study can provide a benchmark for the application of 5GDH systems in heating dominated regions.

Decarbonising industrial heat is a significant challenge due to various factors such as the slow transition to renewable technologies and insufficient awareness of their availability. The effectiveness of commercially available renewable heating systems is not well defined in terms of techno-economic boundaries. This study presents a techno-economic assessment of a novel system designed for steam production at a food and beverage plant. The proposed system is combines parabolic trough collectors with pressurized water thermal storage and photovoltaic-driven high-temperature sand storage. The technological components within the hybrid system complements each other both economically and practically, resulting in cost and land area savings. To evaluate the proposed system, simulations were performed using a model developed in TRNSYS and Python. The combined system exhibits better economic and land use performance than when these technologies are used individually. Specifically, the system has a high solar fraction of 90% while remaining competitive with the existing boiler fuel cost. The study emphasizes the importance of multi-technology approaches in developing practical solutions for industrial heat decarbonization. The findings can guide industries in a transition to sustainable heat sources and contribute to global efforts in mitigating climate change.

Industrial heat production is responsible for around 20% of total greenhouse gas emissions in Europe. To achieve the climate change goals defined in the Paris Climate Agreement, the EU commission has shifted its focus on sustainable means to generate heating. Moreover, global dependencies are leading to a re-organization of natural gas supplies. Therefore, there is a need for less vulnerable and less price-volatile solutions for heating. This paper focuses on two decarbonization technologies for industrial process heat supply: a) electricity-driven steam-generating high-temperature heat pumps (HTHP), a technology that is more efficient than fossil fuel boilers in generating steam, and b) solar parabolic trough collector (PTC), which can produce heat economically and at a minimal carbon footprint compared to other technologies. The main aim of this paper is to evaluate the levelized cost of heat (LCOH) of these technologies to fulfill a comparative techno-economic analysis. A maximum PTC collector's solar fraction limit (SFlimit) is defined to indicate when the LCOH for these two technologies is equal. This allows for distinguishing between the economic stronghold of each technology. The evaluation is carried out through the annual energy simulations using TRNSYS and Excel spreadsheets for HTHPs, while TRNSED and OCTAVE are used for the solar thermal part. Boundary conditions for European geographical constraints have been applied to establish use cases for the analysis. The result shows that the design of a PTC system with optimal SF can reach cost parity with HTHP for most of the analyzed locations. The developed methodology serves as a valuable guide to quickly determine a preferred lower carbon heat solution, thus easing the decision-making for industries