Nuevas estrategias de planificación de la producción en plantas termosolares con almacenamiento térmico

En respuesta a los problemas energéticos actuales, la generación eléctrica basada en energía renovable intermitente, como la energía solar y eólica, ha crecido significativamente durante los últimos años gracias a la disminución de costes. Este tipo de generación presenta un carácter intermitente, variable y de difícil predicción, lo que dificulta su integración en la red eléctrica. Sin embargo, la energía termosolar posee ciertas características que pueden compensar en parte las desventajas anteriores. Esta tecnología captura la radiación solar en forma de energía térmica por medio del calentamiento de un fluido, para más tarde convertirla en electricidad.Por el hecho de emplear energía térmica como forma de energía intermedia, se complementa muy bien con sistemas de almacenamientotérmico. Gracias a este almacenamientoenergético, este tipo de plantas presenta cierto grado de gestionabilidad, existiendo la posibilidad de regular la producción. Esta propiedad favorece su participación en el mercado eléctrico, donde el objetivo del productor de electricidad es maximizar los beneficios económicos derivados de la venta de electricidad. Este objetivo puede lograrse cuando se planifica la producción en función del perfil de precios de venta de la electricidad. Puede plantear se, por tanto, un problema de planificación óptima de la producción. Considerando sólo el mercado diario de la electricidad, la resolución de este problema de optimización permite obtener el plan diario de generación, que debe enviarse al mercado normalmente el día anterior. Se deduce de lo anterior que en el caso de plantas renovables, además de la necesidad de disponer de una predicción de los precios de la electricidad, se requiere una prediccióndel recurso natural para poder abordar el problema. Los objetivos principales de esta Tesis son el diseño de nuevas estrategias de planificaciónóptima de la producción para una planta termosolar con almacenamiento térmico, y el estudio mediante simulación del rendimiento económico de cada estrategia cuando se considera la participación de la planta en el mercado diario de la electricidad. La planificación óptima se obtiene empleando programación lineal entera mixta, que es la herramienta matemática más usada para resolver este tipo de problemas. La primera estrategia realiza una replanificación horaria de la producción, considerando los ingresos derivados de la venta de electricidad en un determinado horizonte temporal y las posibles penalizaciones por desvíos respecto al plan de generación ya comprometido. Esta estrategia permite introducir en el problema la nueva información disponible cada hora, abordando de esta manera la incertidumbre presente en las predicciones y en el propio modelado del problema. La segunda estrategia incluye un mecanismo que penaliza los cambios en la producción. Además, este mecanismo penaliza de manera diferente las variaciones según el estado del bloque de potencia: operación normal, arranque y parada. De esta manera se consigue aumentar el número de grados de libertad del problema en busca de mejores soluciones. Esta reducción de la variabilidad en la generación tiene como ventajas una extensión en la vida útil de los elementos del bloque de potencia, una reducción de sus costes de mantenimiento y una simplificación de la operación. Se propon e una metodoloqía para estimar el máximo nivel de penalización de las variaciones que no perjudique el rendimiento económico. Finalmente, se desarrolló otra estrategia que combina la replanificación horaria con la penalización de las variaciones. El impacto económico de las estrategias anteriores se ha evaluado mediante simulaciones sobre una planta de 50 MW de tipo cilindro parabólico. Se han empleado datos realistas para elrecurso solar, los precios de la electricidad, los costes de penalización y las predicciones de todos estos datos. Los resultados confirman las mejoras esperadas en cada una de las estrategias.In response to current energy problems, electricity generatiOn based on intermittent renewable energy, such as solar and wind energy, has grown significantly in recent years thanks to the decrease in costs. This type of generation has an intermittent, variable and difficult prediction character, which makes it difficult to integrate into the electricity grid. However, solar thermal energy has certain characteristics that can partially compensate for the above disadvantages. This technology captures solar radiation in the form of thermal energy by heating a fluid, to later convert it into electricity. By using thermal energy as a form of intermediate energy, this technology is complemented very well with thermal energy storage systems. Thanks to this energy storage system, this type of plants has a certain degree of dispatchability, with the possibility of regulating production. This property favors its participation in the electricity market, where the objective of the electricity producer is to maximize the economic benefits derived from the sale of electricity. This objective can be achieved when production is scheduled based on the electricity sales price profile. Therefore, an optimal generation scheduling problem may arise. Considering only theday-ahead energy market, the resolution of this optimization problem allows obtaining the daily generation schedule, which must be sent to the market normally the day befare. It follows from the above that in the case of renewable plants, in addition to the need to have a prediction of electricity prices, a forecast of the natural resource is required to address the problem. The main objectíves of this Thesis are the design of new strategies for optímal generation scheduling applied to a concentrating solar power plant, and the study by simulation of the economic performance of each strategy when considering the participation of the plant in the day-ahead energy market. The optimal generation schedule is obtained using mixed integer linear programming, which is the most used mathematical tool to solve these types of problems. The first strategy performs an hourly rescheduling of the generation, considering the revenues derived from the sale of electricity in a certain time horizon and the possible penalties for deviatíons from the generation schedule already committed. This strategy allows to include into the problem the new information available every hour, thus addressing the uncertainty present in the predictions and in the modeling of the problem itself. The second strategy includes a mechanism that penalizes changes in generation. In addition, this mechanism penalizes variations differently according to the state of the power block: normal operation, startup and shutdown. In this way, it is possible to increase the number of degrees of freedom of the problem in seárch of better solutions. This reduction of the variability in the generation has as advantages an extension in the lifetime of the elements of the power block, a reduction of its maintenance costs andan easier plant operability. A methodology is proposed to estimate the maximum level of penalty for variations that does not affect economic performance. Finally, another strategy was developed that combines hourly rescheduling with the penalization of variations. The economic impact of the above strategies has been evaluated through simulations on a 50 MW parabolic trough collector plant. Realistic data for the solar resource, electricity prices, penalty costs and predictions of all these data have been used. The results confirm the expected improvements in each of the strategies

Development of optimal energy management and sizing strategies for large-scale electrical storage systems supporting renewable energy sources.

284 p.El desarrollo e integración de las fuentes de energía renovable (RES) conducirá a un futuro energético más sostenible. Las plantas renovables deberán mejorar su participación y operación a través de los mercados de electricidad de una manera más controlada y segura. Además, el diseño actual del mercado está cambiando para permitir una participación inclusiva en mercados de flexibilidad. En este contexto, los sistemas de almacenamiento de energía (ESS) se consideran una de las tecnologías flexibles clave que pueden apoyar la operación de las energías renovables, mediante servicios como: 1) control de la potencia generada, 2) mejora de los errores de predicción, y 3) provisión de servicios auxiliares de regulación de frecuencia. Sin embargo, el desarrollo del almacenamiento ha sido frenado también por sus altos costos. Por lo tanto, esta tesis doctoral aborda el tema del ¿Desarrollo de estrategias óptimas de gestión y dimensionamiento de los sistemas de almacenamiento eléctrico a gran escala como apoyo a fuentes de energía renovable¿, con el objetivo de desarrollar una metodología con una perspectiva global, mediante una estrategia de gestión de energía avanzada (EMS) que aborda la gestión de activos (RES + ESS) a largo plazo y por otro lado, el cálculo del dimensionamiento y operación del almacenamiento a corto plazo (en la operación en tiempo real), para asegurar un marco adecuado que permita evaluar la rentabilidad de la integración del almacenamiento en aplicaciones conectadas a la red. La estrategia de gestión de energía propuesta es validada a través de dos casos de estudio: una planta renovable individual (eólica o solar) con almacenamiento, y un porfolio de renovables y almacenamiento

Development of optimal energy management and sizing strategies for large-scale electrical storage systems supporting renewable energy sources.

284 p.El desarrollo e integración de las fuentes de energía renovable (RES) conducirá a un futuro energético más sostenible. Las plantas renovables deberán mejorar su participación y operación a través de los mercados de electricidad de una manera más controlada y segura. Además, el diseño actual del mercado está cambiando para permitir una participación inclusiva en mercados de flexibilidad. En este contexto, los sistemas de almacenamiento de energía (ESS) se consideran una de las tecnologías flexibles clave que pueden apoyar la operación de las energías renovables, mediante servicios como: 1) control de la potencia generada, 2) mejora de los errores de predicción, y 3) provisión de servicios auxiliares de regulación de frecuencia. Sin embargo, el desarrollo del almacenamiento ha sido frenado también por sus altos costos. Por lo tanto, esta tesis doctoral aborda el tema del ¿Desarrollo de estrategias óptimas de gestión y dimensionamiento de los sistemas de almacenamiento eléctrico a gran escala como apoyo a fuentes de energía renovable¿, con el objetivo de desarrollar una metodología con una perspectiva global, mediante una estrategia de gestión de energía avanzada (EMS) que aborda la gestión de activos (RES + ESS) a largo plazo y por otro lado, el cálculo del dimensionamiento y operación del almacenamiento a corto plazo (en la operación en tiempo real), para asegurar un marco adecuado que permita evaluar la rentabilidad de la integración del almacenamiento en aplicaciones conectadas a la red. La estrategia de gestión de energía propuesta es validada a través de dos casos de estudio: una planta renovable individual (eólica o solar) con almacenamiento, y un porfolio de renovables y almacenamiento

Optimal generation scheduling for renewable microgrids using hydrogen storage systems

The topic of this thesis is the development of a tool for an optimal energy management strategy (EMS) of the generators and energy storage systems constituent microgrids, both grid-connected or isolated (stand-alone power system) powered by Renewable Energy Sources (RES). In particular, a novel control system is designed based on the resolution of the unit commitment problem. For each time step, the proposed control system compares the expected power produced by the renewable generators with the expected load demand and determines the scheduling of the different energy storage devices and generators for the next few hours, which minimizes the operating cost of the overall microgrid. To take into account for forecasting uncertainties, the generation of the different scenarios is carried out through a discretization of the probability distribution function of the forecasting errors for wind speed, solar radiation and load requests by a set of finite states. A set of various scenarios are therefore analyzed and compared by the control system to find the minimum operating costs. The proposed algorithm is firstly applied to a microgrid at LABH2FER (Sardegna Ricerche, Italy). Since the microgrid is under construction, the expected performance is evaluated through a simulation modeling, implemented in Matlab-Simulink. Furthermore, in order to highlight the benefits of including weather forecasts and operating costs in the EMS, a comparative analysis with a simpler EMS based on control states of storage devices is carried out. The results of the comparative study demonstrate that a reduction of almost 5-10% in the annual operating costs and energy losses is achieved thanks to the implementation of the proposed control system. Moreover, the proposed control strategy is implemented and tested to a microgrid present at the University of Seville. Experimental results demonstrate the feasibility and the actual functionality of the control system. Additional benefits are also observed, such as the reduction in power exchanged with the upstream grid thanks to a better management of the storage systems

Automatic Control of a Parabolic Trough Solar Thermal Power Plant

This thesis is interested in improving the operation of a parabolic trough technology based solar thermal power plant by means of automatic control. One of the challenging issues in a solar thermal power plant, from the control point of view, is to maintain the thermal process variables close to their desired levels. In contrast to a conventional power plant where fuel is used as the manipulated variable, in a solar thermal power plant, solar radiation cannot be manipulated and in fact it ironically acts as a disturbance due to its change on a daily and seasonal basis. The research facility ACUREX is used as a test bed in this thesis. ACUREX is a typical parabolic trough technology based solar thermal power plant and belongs to the largest research centre in Europe for concentrating solar technologies, namely the Plataforma Solar de Almería (PSA) in south-east Spain. The plant exhibits nonlinearities as well as resonance characteristics that lie well within the desired control bandwidth. Failure to adequately capture the resonance characteristics of the plant results in an undesired oscillatory control performance. Moreover, measured disturbances are an integral part of the plant and while some of the measured disturbances do not have a significant impact on the operation of the plant, others do. Hence, with the aim of handling the plant nonlinearities and capturing the plant resonance characteristics, while taking explicit account of the measured disturbances, in this thesis a gain scheduling feedforward predictive control strategy is proposed. The control strategy is based upon a family of local linear time-invariant state space models that are estimated around a number of operating points. The locally estimated linear time-invariant state space models have the key novelty of being able to capture the resonance characteristics of the plant with the minimal number of states and hence, simple analysis and control design. Moreover, while simple classical, series and parallel, feedforward configurations have been proposed and used extensively in the literature to mitigate the impact of the measured disturbances of the ACUREX plant, the proposed control strategy incorporates a feedforward systematically by including the effects of the measured disturbances of the ACUREX plant into the predictions of future outputs. In addition, a target (set point) for a control strategy is normally set at the ACUREX plant by the plant operator. However, in this thesis it is argued that, in parallel, the operator must choose between potentially ambitious and perhaps unreachable targets and safer targets. Ambitious targets can lead to actuator saturation and safer targets imply electricity production losses. Hence, in this thesis a novel two-layer hierarchical control structure is proposed with the gain scheduling feedforward predictive control strategy being deployed in a lower layer and an adequate reachable reference temperature being generated from an upper layer. The generated reference temperature drives the plant near optimal operating conditions, while satisfying the plant safety constraints, without any help from the plant operator and without adding cost. The proposed two-layer hierarchical control strategy has the potential benefits of: (i) maximising electricity production; (ii) reducing the risk of actuator saturation; (iii) extending the life span of various elements of the plant (e.g. synthetic oil, pump and valves) and (iv) limiting the role of the plant operator. The efficacy of the proposed two-layer hierarchical control strategy is evaluated using a nonlinear simulation model that approximates the dynamic behaviour of the ACUREX plant. The nonlinear simulation model is constructed in this thesis and validated in the time and frequency domain

Use, Operation and Maintenance of Renewable Energy Systems:Experiences and Future Approaches

The aim of this book is to put the reader in contact with real experiences, current and future trends in the context of the use, exploitation and maintenance of renewable energy systems around the world. Today the constant increase of production plants of renewable energy is guided by important social, economical, environmental and technical considerations. The substitution of traditional methods of energy production is a challenge in the current context. New strategies of exploitation, new uses of energy and new maintenance procedures are emerging naturally as isolated actions for solving the integration of these new aspects in the current systems of energy production. This book puts together different experiences in order to be a valuable instrument of reference to take into account when a system of renewable energy production is in operation

Sustainability Assessment of Community Scale Integrated Energy Systems: Conceptual Framework and Applications

abstract: One of the key infrastructures of any community or facility is the energy system which consists of utility power plants, distributed generation technologies, and building heating and cooling systems. In general, there are two dimensions to “sustainability” as it applies to an engineered system. It needs to be designed, operated, and managed such that its environmental impacts and costs are minimal (energy efficient design and operation), and also be designed and configured in a way that it is resilient in confronting disruptions posed by natural, manmade, or random events. In this regard, development of quantitative sustainability metrics in support of decision-making relevant to design, future growth planning, and day-to-day operation of such systems would be of great value. In this study, a pragmatic performance-based sustainability assessment framework and quantitative indices are developed towards this end whereby sustainability goals and concepts can be translated and integrated into engineering practices. New quantitative sustainability indices are proposed to capture the energy system environmental impacts, economic performance, and resilience attributes, characterized by normalized environmental/health externalities, energy costs, and penalty costs respectively. A comprehensive Life Cycle Assessment is proposed which includes externalities due to emissions from different supply and demand-side energy systems specific to the regional power generation energy portfolio mix. An approach based on external costs, i.e. the monetized health and environmental impacts, was used to quantify adverse consequences associated with different energy system components. Further, this thesis also proposes a new performance-based method for characterizing and assessing resilience of multi-functional demand-side engineered systems. Through modeling of system response to potential internal and external failures during different operational temporal periods reflective of diurnal variation in loads and services, the proposed methodology quantifies resilience of the system based on imposed penalty costs to the system stakeholders due to undelivered or interrupted services and/or non-optimal system performance. A conceptual diagram called “Sustainability Compass” is also proposed which facilitates communicating the assessment results and allow better decision-analysis through illustration of different system attributes and trade-offs between different alternatives. The proposed methodologies have been illustrated using end-use monitored data for whole year operation of a university campus energy system.Dissertation/ThesisDoctoral Dissertation Civil, Environmental and Sustainable Engineering 201

Power electronics technologies for renewable energy sources

Over the last decades, power grids are facing significant improvements mainly due to the integration of more and more technologies. In particular, renewable energy sources (RES) are contributing to moving from centralized energy production to a new paradigm of distributed energy production. Analyzing in more detail the requirements of the diverse technologies of RES, it is possible to identify a common and key point: power electronics. In fact, power electronics is the key technology to embrace the RES technologies towards controllability and the success of sustainability of power grids. In this context, this book chapter is focused on the analysis of diverse RES technologies from the point of view of power electronics, including the introduction and explanation of the operating principle of the most relevant RES, both in onshore and offshore scenarios. Additionally, are also presented the main topologies of power electronics converters used in the interface of RES.(undefined

Energy Storage Efficiency

Renewable energy sources with their growing importance represent the key element in the whole transformation process worldwide as well as in the national/global restructuring of the energy system. It is important for a sufficient energy system is to find a solution and key element to complete energy supply, that is, energy storage. Reasons and background, which make the energy storage so crucial, imply that exact, enduring development of energy storage is an indispensable part of the full energy supply. There are some necessary components for further development and implementation of renewable energy sources, and these components involve not only a flexible generation system but also network expansion, demand-side integration, and storage. As the energy storage is a much needed component that can facilitate a low carbon energy system, energy storage technologies find their applications in two major areas, and these are electricity network energy storage and transport/mobility. Interest toward energy storage has also grown due to technical and innovative progress in the field of energy storage technologies. Additionally, energy storage can be considered from different perspectives, which always give corresponding benefits, emphasizing the importance and attractiveness of energy storage