• Energy Research

A transition from fossil to renewable energy requires the development of sustainable electric energy storage systems capable to accommodate an increasing amount of energy, at larger power and for a longer time. Flow batteries are seen as one promising technology to face this challenge. As different innovations in this field of technology are still under development, reproducible, comparable and verifiable life cycle assessment studies are crucial to providing clear evidence on the sustainability of different flow battery systems. Based on a review of 20 relevant life cycle assessment studies for different flow battery systems, published between 1999 and 2021, this contribution explored relevant methodological choices regarding the sequence of phases defined in the ISO 14,040 series: goal and scope definition, inventory analysis, impact assessment and interpretation. Inspired by good practice examples, common gaps and weaknesses were identified and recommendations for comparative life cycle assessment studies were derived. This includes suggestions for an expanded functional unit definition, a provision of more detailed and transparent reporting of LCI data while using input/output tables. Outcomes of this study are also of relevance for the amendment of the Batteries Directive 2006/66/EC, where first drafts are under revision in the European Council, including the introduction of a battery passport, which should encourage battery producers to reduce their carbon footprint and avoid problematic materials.

Les réseaux thermiques, qui font partie des micro-réseaux multi-énergies de chaleur et d'électricité, peuvent être confrontés à des problèmes de capacité, de production et de distribution, en raison de l'augmentation de la demande demandée ou de la capacité sous-utilisée, qui est dimensionnée pour les heures de pointe. Les problèmes de sous-capacité peuvent être résolus avec l'expansion de la capacité de production et de pipeline, ce qui entraîne des coûts d'investissement considérables et des coûts de maintenance supplémentaires. En cas de surcapacité, une meilleure utilisation des actifs existants peut générer des revenus supplémentaires et augmenter l'efficacité énergétique globale du micro-réseau multi-énergie. Dans le secteur de l'électricité, il est envisagé d'interconnecter les micro-réseaux via le réseau du système de distribution, car les micro-réseaux peuvent fonctionner à la fois en mode îlot et en mode connecté au réseau. Dans ce travail, de manière similaire, nous proposons l'interconnexion de réseaux thermiques adjacents permettant un échange direct de chaleur entre eux pour augmenter la flexibilité d'approvisionnement des micro-réseaux, aider à répondre aux pics de demande et réduire les coûts opérationnels. Des exemples de micro-réseaux intégrés de chaleur et d'électricité qui pourraient bénéficier d'interconnexions thermiques sont les parcs industriels, les campus universitaires, les hôpitaux et même les complexes résidentiels avec un générateur de chaleur partagé. Cet article présente un modèle de marché pour le transfert de chaleur optimal entre les micro-réseaux de chaleur et d'électricité interconnectés thermiquement. Le modèle résultant est un modèle de programmation quadratique convexe qui permet de dériver des prix de transfert de chaleur qui garantissent un équilibre concurrentiel. En outre, nous avons effectué des tests numériques pour explorer l'impact de la topologie de connexion, de la capacité de transfert d'énergie thermique et de l'efficacité de l'interconnexion sur l'énergie transférée et les prix. Las redes térmicas, parte de las microrredes multienergéticas de calor y energía, pueden enfrentar problemas de capacidad, generación y distribución, ya sea por el aumento de la demanda solicitada o por la capacidad infrautilizada, que está dimensionada para las horas pico. Los problemas de falta de capacidad pueden abordarse con la expansión de la capacidad de generación y tuberías, lo que resulta en costos de capital considerables y costos de mantenimiento adicionales. En el caso de un exceso de capacidad, un mejor uso de los activos existentes puede generar más ingresos y aumentar la eficiencia energética general de la microrred multienergética. En el sector eléctrico, se está considerando la interconexión de microrredes a través de la red del sistema de distribución, ya que las microrredes pueden operar tanto en modo aislado como conectado a la red. En este trabajo, de manera similar, proponemos la interconexión de redes térmicas adyacentes que permitan el comercio directo de calor entre ellas para aumentar la flexibilidad de suministro de las microrredes, ayudar a satisfacer los picos de demanda y reducir los costos operativos. Ejemplos de microrredes integradas de calor y energía que podrían beneficiarse de las interconexiones térmicas son parques industriales, campus universitarios, hospitales e incluso complejos residenciales con un generador de calor compartido. Este documento presenta un modelo de mercado para la transferencia de calor óptima entre microrredes de calor y energía interconectadas térmicamente. El modelo resultante es un modelo de programación cuadrática convexa que permite la derivación de precios de transferencia de calor que garantizan un equilibrio competitivo. Además, realizamos pruebas numéricas para explorar el impacto de la topología de conexión, la capacidad de transferencia de energía térmica y la eficiencia de interconexión en la energía transferida y los precios. Thermal networks, part of heat-and-power multi-energy microgrids, may face capacity issues, generation and distribution ones, either due to the increase in the requested demand or capacity underused, which is sized for peak hours. Under-capacity issues may be addressed with generation and pipeline capacity expansion, resulting in considerable capital costs and extra maintenance costs. In the case of over-capacity, better usage of the existing assets may bring further revenues and increase the multi-energy microgrid's overall energy efficiency. In the electricity sector, it is being considered the interconnection of microgrids via the distribution system network, since microgrids can operate in both islanded and network-connected modes. In this work, in a similar fashion, we propose the interconnection of adjacent thermal networks enabling direct heat trading among them to increase the micro-grids' supply flexibility, help meeting demand peaks, and reduce operational costs. Examples of integrated heat-and-power microgrids that could benefit from thermal interconnections are industrial parks, university campuses, hospitals, and even residential complexes with a shared heat generator. This paper presents a market model for the optimal heat transfer between thermally interconnected heat-and-power microgrids. The resulting model is a convex quadratic programming model that enables the derivation of heat transfer prices that guarantee a competitive equilibrium. Furthermore, we performed numerical tests to explore the impact of connection topology, thermal power transfer capacity, and interconnection efficiency on transferred energy and prices. قد تواجه الشبكات الحرارية، وهي جزء من الشبكات الدقيقة متعددة الطاقة للحرارة والطاقة، مشكلات في السعة، ومشكلات في التوليد والتوزيع، إما بسبب الزيادة في الطلب المطلوب أو السعة غير المستخدمة بشكل كافٍ، والتي يتم تحديد حجمها لساعات الذروة. يمكن معالجة مشكلات نقص السعة من خلال توسيع سعة التوليد وخطوط الأنابيب، مما يؤدي إلى تكاليف رأسمالية كبيرة وتكاليف صيانة إضافية. في حالة الطاقة الفائضة، قد يؤدي الاستخدام الأفضل للأصول الحالية إلى تحقيق المزيد من الإيرادات وزيادة كفاءة الطاقة الإجمالية للشبكة الدقيقة متعددة الطاقة. في قطاع الكهرباء، يتم النظر في الربط البيني للشبكات الصغيرة عبر شبكة نظام التوزيع، حيث يمكن للشبكات الصغيرة أن تعمل في كل من الأوضاع الجزيرية والمتصلة بالشبكة. في هذا العمل، وبطريقة مماثلة، نقترح الربط البيني للشبكات الحرارية المجاورة مما يتيح التداول المباشر للحرارة فيما بينها لزيادة مرونة العرض للشبكات الصغيرة، والمساعدة في تلبية قمم الطلب، وتقليل التكاليف التشغيلية. ومن الأمثلة على الشبكات الدقيقة المتكاملة للحرارة والطاقة التي يمكن أن تستفيد من الترابطات الحرارية المجمعات الصناعية والحرم الجامعي والمستشفيات وحتى المجمعات السكنية ذات مولد الحرارة المشترك. تقدم هذه الورقة نموذج سوق لنقل الحرارة الأمثل بين الشبكات الدقيقة المترابطة حراريًا للحرارة والطاقة. النموذج الناتج هو نموذج برمجة تربيعي محدب يمكّن من اشتقاق أسعار نقل الحرارة التي تضمن توازنًا تنافسيًا. علاوة على ذلك، أجرينا اختبارات عددية لاستكشاف تأثير طوبولوجيا الاتصال، وقدرة نقل الطاقة الحرارية، وكفاءة التوصيل البيني على الطاقة والأسعار المنقولة.

The need for secure and flexible operation of distribution power systems with renewable generation and the decline in battery prices have made energy storage projects a viable option. The storage characterization currently utilized for power system models relies on two significant assumptions: the storage efficiency and power limits are constant. This approach can lead to an overestimation of the available battery power and energy, thus, threatening the system reliability. We introduce a stochastic operating model for distribution systems with non-ideal energy storage, that allows the purchasing of energy and reserves from the electricity market through the interconnection with the transmission system. The model's objective is the centralized minimization of the operational costs derived from the energy and reserves purchase at the electricity market, as well as those incurred while operating the system's fuel-based and renewable generation, and energy storage system. The proposed energy storage model is computationally validated and compared on a modified IEEE 33-bus electric distribution system.

Abstract A novel configuration of a hybrid binary geothermal biomass power plant is proposed that generates electricity through the Organic Rankine Cycle (ORC), which receives the thermal power provided by a biomass heat source through intermediate geothermal fluid. The plants are located in regions with extreme environmental conditions where water is not available, making the use of air-cooled condensers in the ORC necessary, and the seasonal variations of the ambient air temperature are remarkable. As a further novel aspect, the modification of the biomass mass flow rate is used to overcome the simultaneous harmful effects of a considerable reduction in the geothermal fluid temperature during the operative life of the plant and the more significant seasonal change of the ambient air temperature. Our original approach involves developing a simulation model of the proposed plant using the commercial software Aspen® to determine the energy performance in off-design conditions, i.e., in the presence of the simultaneous changes of the biomass flow rate, ambient air temperature and geothermal fluid temperature. The biomass flow rate is controlled to maximize the net electric power or net thermodynamic efficiency of the plant with varying ambient air and geothermal fluid temperatures. In comparison to the first operating mode, the second enables a saving of the biomass used annually in the range of 28.3%–42.6%, corresponding to the maximum and minimum geothermal fluid temperature, respectively, with the resulting detrimental effect on the yearly produced electric energy in the range of 9%–23.6%.

Currently, the characterization of electric energy storage units used for power system operation and planning models relies on two major assumptions: charge and discharge efficiencies, and power limits are constant and independent of the electric energy storage state of charge. This approach can misestimate the available storage flexibility. This work proposes a detailed model for the characterization of steady-state operation of Li-ion batteries in optimization problems. The model characterizes the battery performance, including non-linear charge and discharge power limits and efficiencies, as a function of the state of charge and requested power. We then derive a linear reformulation of the model without introducing binary variables, which achieves high computational efficiency, while providing high approximation accuracy. The proposed model characterizes more accurately the performance and technical operational limits associated with Li-ion batteries than those present in classical ideal models. The developed battery model has been compared with three modelling approaches: the complete non-convex formulation; an ideal model typically used in the power system community; and a mixed integer linear reformulation approach. The models have been tested on a network-constrained economic dispatch for a 24-bus system. Based on the simulations, we observed approximately 12% of energy mismatches between schedules that use an ideal model and those that use the model proposed in this study.

The study of the impact of the zero-emissions scenarios of several countries on the electrical demand is relevant to analyze the feasibility of the sustainable energy transition. This paper presents a structured method to assess the effect of the 100 % renewable scenario on the hourly electrical load profile of a country taking Italy as reference case study. The hourly discretization is a fundamental approach to evaluate the contribution of the intermittent renewable sources during the day and the proposed methodology can be easily applied to several countries' scenarios. Numerous decarbonization scenarios consider the adoption of electricity in several sectors. Consequently, the primary energy reduction (40 % in the scenario considered) is usually accompanied by a relevant increase of the annual electricity demand (94%–124 %). In this paper, each sector's contribution is estimated separately, and the results show demand peaks above 100 GW and a baseload above 50 GW, which is more than double that of recent years. Electricity consumption is higher in the colder months and hydrogen and synthetic fuel production impacts significantly on the total electricity demand (26%–32 %). The results of this work will be used to verify the feasibility of net zero scenarios with hourly discretization in further research analysis.

This paper presents a zero-dimensional dynamic model of redox flow batteries (RFBs) for the system-level analysis of energy loss. The model is used to simulate multi-cell systems considering the effect of design and operational parameters on energy loss and overall performance. The effect and contribution of stack losses (e.g., overpotential and crossover losses) and system losses (e.g., shunt currents and pumps) to total energy loss are examined. The model is tested by using literature data from a vanadium RFB energy storage. The results show that four parameters mainly affect RFB system performance: manifold diameter, stack current, cell standard potential, and internal resistance. A reduction in manifold diameter from 60 mm to 20 mm reduced shunt current loss by a factor of four without significantly increasing pumping loss, thus boosting round-trip efficiency (RTE) by 10%. The increase in stack current at a low flow rate increases power, while the cell standard potential and internal resistance play a crucial role in influencing both power and energy output. In summary, the modeling activities enabled the understanding of critical aspects of RFB systems, thereby serving as tools for system design and operation awareness.