A load-based approach for optimizing a packed-bed thermal store

This paper presents a load-based optimization approach for improving the efficiency of a packed bed. The optimization is based on splitting the work-cycle of the thermal store into two frequency components: low and high. A packed bed is designed for each one of the two profiles. A packed bed can be customised much better for a duty-cycle that contains a narrow range of frequencies.The case study presented considers a 24 h working-cycle (12 h charge / 12 h discharge) with a 10 MW peak power and an exergy storage requirement of 33.3 MW h (76.3 MW h of heat). A packed bed was optimized for this duty-cycle using a one dimensional model that varies the aspect ratio and the rock size. This packed bed is the ‘reference case’ for the study. The aim of the load-based optimization is to create a two-bed system that achieves lower exergy losses than the reference case while keeping the overall storage capacity constant.A sign-preserving filter is used as the signal-splitting tool. Numerous different work-cycle “splits” are explored. Results show that the exergy losses of the packed bed can be considerably reduced. The optimum work-cycle split considers a low-frequency packed bed that supplies 85% of the storage capacity and a high-frequency packed bed that provides the remaining 15%. The combined losses of the two packed beds are 644 kW h, which represents a reduction of 25.5% in comparison to the exergy losses of the reference case. The study demonstrates that the “load-based optimization” allows replacing a packed bed with an equivalent but more efficient two-bed system at almost no additional cost

Análisis de los partidos políticos mediante indicadores convencionales y de gestión: el caso de Podemos e Izquierda Unida

Universidad de Sevilla. Grado en Finanzas y Contabilida

Pre‐historic eating patterns in Latin America and protective effects of plant‐based diets on cardiovascular risk factors

In this review, we present the contributions to nutrition science from Latin American native peoples and scientists, appreciated from a historic point of view since pre‐historic times to the modern age. Additionally, we present epidemiological and clinical studies on the area of plant‐based diets and their relation with the prevention and treatment of cardiovascular diseases conducted in recent decades, and we discuss challenges and perspectives regarding aspects of nutrition in the region

A directly charged thermal store for compressed air energy storage systems

This paper discusses the design of a heat storage unit with integrated heat exchangers (TES + HX), which is intended to work in a Compressed Air Energy Storage (CAES) system. The unit can be charged directly by the system's stream of pressurised air, eliminating the need for additional heat exchangers and reducing the number of heat transfer processes. Silica sand is used as the storage medium due to its high heat capacity, non-corrosivity and its ability to accommodate the thermal expansion of steel pipes.A medium-scale, medium-duration CAES system (250 kW/1MWh) is used as a case study. The heat storage subsystem comprises a packed-bed thermal store, three air-to-air heat exchangers and an ambient pressure air blower. Combined, this subsystem has an approximate cost of £147k and achieves an efficiency of ∼89 %, which translates into a levelized cost of ∼48.5 £/MWh. An integrated TES + HX unit can achieve a levelized cost of ∼35 £/MWh. The unit has an estimated cost of £38.5k and achieves an overall roundtrip exergy efficiency of ∼91.8 %. The integrated TES + HX unit not only offers a significant reduction in the capital cost of a CAES system and an efficiency improvement, but it also allows for a simpler overall architecture

Load optimization for reducing the cost of an electric vehicle’s battery pack

This paper presents a study on the cost-optimization of the battery pack of a Nissan Leaf. The optimization is based on decomposing the load that the battery pack experiences into two components (low and high frequency), each of which will be handled by an independent battery. The reduction in cost comes from the possibility of manufacturing batteries of different specifications whose cost per unit energy ($/kWh) and per unit power ($/kW) differ considerably from each other. The battery used for the low frequency part of the load will have a low cost per unit energy capacity and a higher cost per unit power whilst the fast-frequency battery is the reverse case.Two case studies have been carried out. The first one uses the load profile seen by the battery pack when the car is subjected to the EPA-LA92 driving cycle. The second case study considers a modified profile with a much higher crest factor. A sign-preserving filter is used in the study to perform the signal splitting. A two-dimensional search space is created with the two control parameters of the filter and numerous different “splits” are explored.Results show than an important reduction in the cost of the battery pack can be achieved. In the optimum configuration found—for the case study carried out with the modified profile—the low-frequency battery supplies 80.14% of the total capacity of the car (24 kWh) and sees a maximum peak power of 37.17 kW; whereas the fast-frequency battery has a smaller capacity of 4.77 kW h but sees a much larger peak power of 88.56 kW. The total cost of this hybrid system is estimated at $5939, which represents a 12.7% reduction in cost with respect to the original battery pack of the vehicle

A sign-preserving filter for signal decomposition

There are optimization problems in which an improvement in performance or a reduction in cost can be attained if the input signal of the system is split into multiple components. Splitting the signal allows customizing the design of the system’s hardware for a narrower range of frequencies, which in turn allows making a better use of its physical properties. There exist applications that have very specific signal-splitting requirements, such as ‘counter-flow avoidance’, that conventional signal processing tools cannot meet. Accordingly, a novel ‘Sign-Preserving’ filter has been developed and is presented in this article. The underlying algorithm of the filter is comprehensively explained with the aim of facilitating its reproduction, and the aspects of its operation are thoroughly discussed. The filter has two key features: (1) it separates a discrete signal a into two components – a mostly low-frequency signal b and a predominantly high-frequency signal c such that the sum of b and c replicates exactly the original signal a and, more importantly, (2) the signs of the two output signals are equal to the sign of a at all times. The article presents two case studies which demonstrate the use of the Sign-Preserving filter for the optimization of real-life applications, in which counter-flow must be avoided: the hybridization of the battery pack of an electric vehicle and the parallelization of a packed bed thermal energy store

Short-, medium-, and long-duration energy storage in a 100% renewable electricity grid: A UK case study

Energy storage will be required over a wide range of discharge durations in future zero-emission grids, from milliseconds to months. No single technology is well suited for the complete range. Using 9 years of UK data, this paper explores how to combine different energy storage technologies to minimize the total cost of electricity (TCoE) in a 100% renewable-based grid. Hydrogen, compressed air energy storage (CAES) and Li-ion batteries are considered short-, medium-, and long-duration energy stores, respectively. This paper analyzes different system configurations to find the one leading to the lowest overall cost. Results suggest that the UK will need a storage capacity of ~66.6 TWh to decarbonize its grid. This figure considers a mix of 85% wind + 15% solar-photovoltaics, and 15% over-generation. The optimum distribution of the storage capacity is: 55.3 TWh in hydrogen, 11.1 TWh in CAES and 168 GWh in Li-ion batteries. More than 60% of all energy emerging from storage comes from medium-duration stores. Based on current costs, the storage capacity required represents an investment of ~£172.6 billion, or approximately 8% of the country’s GDP. With this optimum system configuration, a TCoE of ~75.6 £/MWh is attained

The effect of a nuclear baseload in a zero-carbon electricity system: An analysis for the UK

This paper explores the effect of having a nuclear baseload in a 100% carbon-free electricity system The study analyses numerous scenarios based on different penetrations of conventional nuclear, wind and solar PV power, different levels of overgeneration and different combinations between medium and long duration energy stores (hydrogen and compressed air, respectively) to determine the configuration that achieves the lowest total cost of electricity (TCoE). At their current cost, new baseload nuclear power plants are too expensive. Results indicate the TCoE is minimised when demand is supplied entirely by renewables with no contribution from conventional nuclear. However, small modular reactors may achieve costs of ∼£60/MWh (1.5× current wind cost) in the future. With such costs, supplying ∼80% of the country's electricity demand with nuclear power could minimise the TCoE. In this scenario, wind provides the remaining 20% plus a small percentage of overgeneration (∼2.5%). Hydrogen in underground caverns provides ∼30.5 TWh (81 days) of long-duration energy storage while CAES systems provide 2.8 TWh (∼8 days) of medium-duration storage. This configuration achieves costs of ∼65.8 £/MWh. Batteries (required for short duration imbalances) are not included in the figure. The TCoE achieved will be higher once short duration storage is accounted for

The effect of repeated sprint ability on physiological and physical profiles of young basketball players. [El efecto de esprines repetidos en los perfiles fisiológicos y físicos de jóvenes jugadores de baloncesto].

The purpose of this study was to describe the dynamics of a repeated sprint ability (RSA) cycling protocol in young elite basketball players. Twenty-two elite male basketball players (aged 18.3±0.6 years; training years 9.1±1.3 years) performed 3 bouts of a repeated sprint ability (RSA) protocols, consisting of 5 x 6-s cycling sprints with a 24-s rest interval between sprints. The work decrement during the first trial was high (14.1±4.8%) and after 5-minute rest did not change significantly. The total work decreased by 5.5% in the second work interval and by 2.9% in the third interval. During the 5-minute passive rest, young basketball players’ peak power recovered about 90% of the initial levels. It is suggested that rest intervals are sufficient to continue the game with adequate performance potential. A reduction in work decrement, while maintaining the capacity of all sprints, is needed to achieve a higher repeated sprint ability. Resumen El propósito de este estudio fue describir la dinámica de un protocolo de esprines repetidos en jóvenes jugadores de baloncesto. Veintidós jugadores de baloncesto masculino (con edades comprendidas entre 18,3 ± 0,6 años, años de entrenamiento de 9,1 ± 1,3 años) realizaron 3 series de un protocolo de esprín repetido, consistiendo en 5 esprines en cicloergometro de 6-s con de descanso de 24-s entre esprints. La disminución del trabajo durante la primera serie fue alta (14.1 ± 4.8%) y después de 5 minutos de descanso no cambió significativamente. El trabajo total disminuyó en un 5.5% en la segunda serie y en un 2.9% en la tercera. Durante el descanso pasivo de 5 minutos, la potencia máxima de los jóvenes jugadores de baloncesto recuperó aproximadamente hasta un 90% de los niveles iniciales. Se sugiere que los intervalos de descanso sean suficientes para continuar el juego con un potencial de rendimiento adecuado. Se necesita una reducción en el decremento del trabajo, mientras se mantiene la capacidad de todos los esprines, para optimizar esta capacidad de rendimiento tan importante en baloncesto