Multi-state optimal power dispatch model for power-to-power systems in off-grid hybrid energy systems: A case study in Spain

The electricity production from Renewable Energy (RE) in isolated locations requires long-term energy storage systems. To that end, Hybrid Energy Storage Systems (HESS), through a combination of hydrogen and batteries, can benefit from the different advantages of both technologies. This paper presents a hybrid Power-to-Power (PtP) Optimal Power Dispatch (OPD) model for isolated systems with no electric grid access. Currently, the electricity supply in such cases is usually based on a mix of RE as the primary energy source sustained by a diesel genset acting as a backup generator. In this context, the model delivers the hourly energy flows between renewable production sources, energy storage devices and the electrical load, which minimises costs and Green House Gases (GHG) emissions. For validation purposes, the model was tested through its application to a case study in an isolated area in the Canary Islands, Spain. The results show that the algorithm calculates the hourly OPD successfully for a given plant sizing, considering the defined operational states of the different assets. These operational constraints showed a decrease in the PtP round-trip efficiency of 5.4% and a reduction of the hydrogen production of 9.7%. Finally, the techno-economic analysis of the results proves that the combination of hydrogen and batteries with RE production is a feasible alternative to phasing out fossil fuels for the selected case study – reducing the diesel generator usage down to 1.2% of the yearly energy supply

Phasing out steam methane reformers with water electrolysis in producing renewable hydrogen and ammonia: A case study based on the Spanish energy markets

Deploying renewable hydrogen presents a significant challenge in accessing off-takers who are willing to make long-term investments. To address this challenge, current projects focus on large-scale deployment to replace the demand for non-renewable hydrogen, particularly in ammonia synthesis for fertiliser production plants. The traditional process, involving Steam Methane Reformers (SMR) connected to Haber-Bosch synthesis, could potentially transition towards decarbonisation by gradually integrating water electrolysis. However, the coexistence of these processes poses limitations in accommodating the integration of renewable hydrogen, thereby creating operational challenges for industrial hubs. To tackle this issue, this paper proposes an optimal dispatch model for producing green hydrogen and ammonia while considering the coexistence of different processes. Furthermore, the objective is to analyse external factors that could determine the appropriate regulatory and pricing framework to facilitate the phase-out of SMR in favour of renewable hydrogen production. The paper presents a case study based in Spain, utilising data from 2018, 2022 and 2030 perspectives on the country's renewable resources, gas and electricity wholesale markets, pricing ranges, and regulatory constraints to validate the model. The findings indicate that carbon emissions taxation and the availability and pricing of Power Purchase Agreements (PPAs) will play crucial roles in this transition - the carbon emission price required for total phasing out SMR with water electrolysis would be around 550 EUR/ton CO2

Clima y ocupaciones en la Galería de Estatuas (Atapuerca, Burgos) en los últimos 14.000 años: Relatos de una estalagmita

Los espeleotemas constituyen uno de los principales registros para establecer secuencias evolutivas paleoclimáticas del Cuaternario. Además, en cavidades que presentan evidencias de ocupación humana registran los cambios ambientales producidos en el interior de las mismas como resultado de las actividades llevadas a cabo. La estalagmita llargi, procedente de la Galería de Estatuas (Atapuerca, Burgos) representa un archivo de los principales acontecimientos de los últimos 14 Ka de la historia de la cavidad, reflejados en la microestratigrafía, mineralogía y fábrica de crecimiento. La importante humana en el desarrollo de la estalagmita queda registrada en las láminas oscuras de calcita por la presencia de fragmentos de huesos y carbón, y ceniza

Online distribution strategies: A mix of globalization and diversification in the fashion market

The growing importance of online channels, social media, and mobile commerce (m-commerce) has given rise to new retail formats, that use only channel used and which have enabled many new consumers to access certain establishments despite geographical barriers. The fashion sector may be one of the most heavily affected by these developments, due to the highly seasonal nature of the products, keen competitive rivalry, widespread reliance on outsourcing, high brand power variety of pricing policies, and strong emotional implications for consumers, who identify with specific brands. This chapter aims at analyzing the main strategies that retail operators are currently following in the industry in order to differentiate from other retailers. A special interest will be placed on the role of the brand, examining how retailers in the industry use private labels as a differentiation resource. The authors also review the case of ASOS, a global retailer which has proven able to adapt to every market, with a view to determining how it has dealt with the myriad challenges involved. © 2018 by IGI Global

The red coloration of Goikoetxe Cave’s speleothems (Busturia, Spain): An indicator of paleoclimatic changes

The most commonly used paleoclimatic proxies in speleothem studies are the carbon and oxygen stable isotopes and the trace elements of calcite. However, assessing the incorporation of other components, such as organic matter, may also be of interest in interpreting and reconstructing the climate during speleothem growth. In this work, the incorporation of humic and fulvic acids derived from overlying soils is proposed as the cause of the red coloration of speleothems from the Goikoetxe Cave (Busturia, Bizkaia). Through the application of petrological studies combined with X-ray fluorescence, UV luminescence, Raman spectroscopy and Fourier-transform infrared spectroscopy (FTIR) analysis, it has been possible to correlate a variation of organic content in the overlying soils and the red coloration, being this stain a main proxy to study and reconstruct the seasonal paleoclimatic parameters during the speleothem formation

Uso del metaheurístico GRASP en la construcción de árboles de clasificación

This paper proposes a new method for constructing binary classification trees. The aim is to build simple trees, i.e. trees which are as uncomplicate as possible, thereby facilitating interpretation and favouring the balance between optimization and generalization in the test data sets. The proposed method is based on the metaheuristic strategy known as GRASP in conjunction with optimization tasks. Basically, this method modifies the criterion for selecting the attributes that determine the split in each node. In order to do so, a certain amount of randomisation is incorporated in a controlled way. We compare our method with the traditional method by means of a set of computational experiments. We conclude that the GRASP method (for small levels of randomness) significantly reduces tree complexity without decreasing classification accuracy.En este trabajo se propone un nuevo método para la construcción de árboles binarios de clasificación. El objetivo es la construcción de árboles sencillos, es decir, con la menor complejidad posible, lo cual hace que sean de fácil interpretación y propicia el equilibrio entre optimización y generalización en los conjuntos test. El método propuesto se basa en la estrategia metaheurística GRASP usada en la literatura en problemas de optimización. El método básicamente modifica la forma de elección del atributo que determina la partición en cada nodo. Para ello incorpora aleatoriedad de forma controlada. A través de una serie de experimentos computacionales se compara nuestro método GRASP con la forma tradicional de seleccionar atributos. Se puede concluir que nuestro método GRASP, con pequeños niveles de aleatoriedad, consigue árboles significativamente menos complejos que los obtenidos con la forma tradicional

Estudio paleoambiental a partir de precipitados químicos: espeleotemas de la Sala Roja (Cueva Goikoetxe, Busturia, Bizkaia)

El estudio de la evolución geológica de la cueva de Goikoetxe muestra las distintas secuencias de relleno de la cavidad haciendo posible diferenciar dos secuencias aloestratigráficas que incluyen tanto depósitos de relleno detrítico como de precipitado químico, alternando con eventos erosivos. Dichas secuencias permiten reconstruir la historia de la cavidad durante el transcurso de su formación. En relación a los precipitados de origen químico, han podido diferenciarse al menos tres generaciones de espeleotemas, con dos fases de formación de estalagmitas bien diferenciadas: Antuá (basculada debido a una erosión en la cavidad) y Moreno (de desarrollo vertical sobre Antúa y por tanto de génesis posterior). A partir del estudio petrográfico de estos espeleotemas, se han diferenciado distintas fases de crecimiento por cambios ambientales. Futuros análisis mediante catodoluminiscencia y microscopio electrónico permitirán establecer con mayor precisión la evolución paleoambiental del entorno, mientras que el análisis geoquímico determinará la razón de la coloración de las estalagmitas presentes en esta cueva. Además, también se realizarán dataciones U/Th con el fin de saber la edad exacta de cada proceso.Peer Reviewe