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Phase change materials (PCM) are used in many industrial and residential applications for their advantageous characteristic of high capacity of latent thermal storage by means of an isothermal process. In this context, it is very useful to have predictive mathematical models for the analysis of the thermal performance and for the thermal design of these layers. In this work, an experimental validation of an analytical model that resolves the steady periodic heat transfer problem in a finite layer of PCM is presented. The experimental investigation was conducted employing a PCM with thermophysical and thermochemical behavior very close to those hypothesized in the formulation of the analytical model. For the evaluation of the thermophysical properties of the PCM sample used, an experimental procedure created by the authors was employed. In all tests realized in a sinusoidal and non-sinusoidal periodic regime, the comparison between the measured and calculated trends of the temperature at different sample heights and of the surface heat fluxes show an excellent agreement. Moreover, also having verified the analytical total stored energy, the analytical model constitutes a valid instrument for the evaluation of the latent and sensible contribution and the trend in time of the position of the bi-phase interface. Peer Reviewed

The increasing decarbonisation of the power and heat sectors in Great Britain poses numerous uncertainties about the future of the gas network. An optimisation model was developed for investigating the operation of future low carbon electricity, gas and heat supply systems. The model was employed to quantify the impacts on the operation of the gas network in Great Britain of transitioning to low carbon power and heat. The modelling results show that the decarbonisation of the power and heat sectors affects the operation of the high and low pressure gas networks differently. A highly electrified heat sector, only slightly changes the gas load duration curve for the high pressure gas transmission network, but significantly affects the load duration curve for low pressure gas distribution networks. In addition, in a future energy system with a large capacity of variable wind and solar generation, and highly electrified heat supply, although the annual volume of gas supply decreases, the peak gas supply during low wind and cold spells remains the same or even exceeds the current figure. This is mainly due to gas-fired power plants operating to their maximum capacity to complement the wind resource and also supply electricity for heat pumps.

Energy communities (ECs) offer a promising solution for achieving sustainable and decentralized energy systems. However, the successful establishment and operation of ECs requires overcoming barriers that can hinder stakeholder participation. Existing research has primarily focused on incentives and motivations to join ECs, thus neglecting a comprehensive understanding of the key barriers affecting EC stakeholders in European Union (EU) countries. This paper aims to fill this research gap by identifying and ranking the barriers to joining ECs in the EU context with focus on Spain and Italy. To accomplish this, a framework of barriers was developed based on 20 in-depth interviews with diverse stakeholders of established ECs and a survey (n=56). The barriers identified were categorized into four types: (a) financial, (b) regulatory and bureaucratic, (c) technical and practical, and (d) social and cultural. The analytical hierarchical process (AHP) methodology was employed to estimate and rank these barriers. The findings highlight that the most significant barrier categories are regulatory and bureaucratic, and financial. Specifically, regulatory complexity and legal limitations emerge as the top-ranked barriers among the obstacles identified to joining ECs by research participants.

Abstract A new residential district will be built in Innsbruck, Austria. The energy and environmental impact are considered during the decision-making procedure. A complete and comprehensive simulation study was performed to develop a decision support tool with respect to a) which type of heating system i.e. heat pumps, connection to district heating, or natural gas boilers, b) which level of centralization of the heating system i.e. from one central solution for the entire district up to decentral systems located in each flat, c) which type of heat distribution system and d) the corresponding pipe insulation level. To compare the aforementioned combinations, various key performance indicators were calculated, using two different calculation methods: one with annual and one with monthly conversion factors. The results show that the use of heat pumps or district heating instead of gas boilers decreases the carbon emissions by a maximum of 75% and 52%, respectively. The choice of the appropriate key performance indicator and calculation method had a minor influence on the ranking of the investigated solutions but a significant influence on the quantitative results.

Computer-based simulations of Organic Rankine Cycles (ORC) have been extensively used in the last two decades to predict the behaviour of existing plants or already in the design phase. For time-varying heat sources, researchers typically rely on either quasi-steady state or dynamic simulations. In this work, the two approaches are compared and the trade-off between them is analysed, taking as benchmark waste heat recovery with ORC from a billet reheating furnace. The system is firstly optimized in MATLAB® using a quasi-steady state approach. The results are then compared with a corresponding dynamic simulation in Dymola. In the case of waste heat from billet reheat furnace, the quasi-steady state approach can successfully capture the fluctuations in waste heat. For heat source ramps from 110% to 40% the nominal value in 30 s, dynamic effects lead to 1.1% discrepancies in ORC net power. The results highlight the validity of the quasi-steady state approach for techno-economic optimization of ORC for industrial waste heat and provide a valuable guideline for developers, companies and researchers when choosing the most suitable tool for their analysis, helping them save time and costs to find the most appropriate approach.

Abstract Increasing demand response (DR) from households, industry and tertiary sector may provide substantial flexibility in renewable-based energy systems, but the deployment of DR is currently limited. This study examines the future economic potential DR in the renewable rich northern European region, and also analyses power markets impacts of large-scale DR deployment in the region. For the quantifications, the energy system model BALMOREL is used, modified to include a detailed temporal modelling of available DR potentials. Results show that among the DR options analysed, space heating and water heating provide the highest shares of loads shifted. The overall demand response potential is particularly high in Norway and Sweden, due to wide-spread electric space- and water heating. Low variable costs make these DR applications economically feasible for deployment, despite high supply-side flexibility provided by regulated hydro power. DR may contribute to peak shaving of up to 18.6% of total peak load in 2050. Revenues from DR-application yield very different results depending on techno-economic parameters, potentials and the price volatility in the various analysed market areas. Results show an insignificant change in CO2 emissions between scenarios with and without demand response.

Energy system models often rely on assumptions about the infeed of renewable energies. Despite their significance, the renewable time series are often based on single weather years, selected without applying clear criteria. For planning purposes of photovoltaic plants or heating and cooling systems, it is common practice to artificially create weather years composed of months from different years. However, there are only few models for the composition of artificial weather years that represent a well-defined high- or low-infeed-scenario. A new method is proposed to artificially construct infeed time series on system level. Under the assumption of a normal distribution, we compose an infeed time series which aims at meeting a certain quantile of annual infeed. Thus, it is possible to construct different infeed scenarios, to model the inter-year variability of the renewable infeed. The method at hand can be useful for everyone who uses exogenous infeed time series in energy modeling.

To phase out fossil fuels, energy systems must shift to renewable electricity as the main source of primary energy. In this paper, we analyze how electrification can support the integration of fluctuating renewables, like wind and PV, and mitigate the need for storage and thermal backup plants. Using a cost-minimizing model for system planning, we find substantial benefits of electricity demand in heating, transport, and industry adapting to supply. In Germany, flexible demand halves the residual peak load and the residual demand and reduces excess generation by 80%. Flexible operation of electrolyzers has the most significant impact accounting for 42% of the reduction in residual peak load and 59% in residual demand. District heating networks and BEVs also provide substantial flexibility, while the contribution of space and process heating is negligible. The results are robust to restrictions on the expansion of the transmission grid. Energy, 278 (Part A) ISSN:0360-5442 ISSN:1873-6785

Based on a sub-critical ORC (Organic Rankine Cycle) process, this study introduces the term OHST (Optimal Heat Source Temperature) with consideration of a suitable thermal match between heat source and working fluid. A theoretical formula is developed for predicting the OHST, which shows that OHST only depends on evaporation pressure and pinch point in the preheater and evaporator. A comparative study between the predicted OHSTs and those obtained from cycle simulations is performed, showing that the proposed formula is reliable, provided that HTF (Heat Transfer Fluid) is homogeneous and has good consistency in terms of heat capacity for different temperatures. To demonstrate the application of the proposed OHST-theory for thermodynamic optimization of ORC systems, a case study is presented based on a simple ORC coupled with thermal water at 140 °C. Consequently, using R227ea leads to the highest system efficiency of 10.38%, due to a better thermal match in the preheater and evaporator. In order to increase the exploitation of the thermal potential from the heat source, a dual-fluid-ORC is proposed, where R245fa and R227ea are considered for the high and low temperature ORC processes, respectively. Finally, this combination leads to the highest system efficiency of 11.07%.