Solar-plus-storage benefits for end-users placed at radial and meshed grids: An economic and resiliency analysis

[EN] A resilient photovoltaic system, which comprises from the joint use of photovoltaic solar panels and electrochemical storage that is able to operate both with and without grid connection, is capable of providing an added service both during normal grid-connected operation and when a blackout occurs (as opposed to a traditional solar system). When the conventional power grid is in normal operation, resilient photovoltaic systems are able to generate revenue and/or reduce the electricity bill. During blackouts, resilient photovoltaic systems are capable of providing critical emergency power to help backup diesel generator systems. The research presented here evaluates the technical and economic feasibility of systems based on photovoltaic solar energy and electrochemical storage in three critical infrastructures which have to account with a typical backup diesel generator. To this end, the research presented here assigns a monetary value to the cost of avoiding a blackout. Thus, the REopt Lite software has been used to optimally select and dimension different resilient schemes. For each of the cases evaluated the resilient systems were able to obtain benefits associated with the substitution of the energy use of the electricity grid, the reduction of charges for the use of energy during peak energy periods, and the modification of energy purchase periods from periods of high cost to periods of low cost. For all cases the model found the optimal combination of technologies capable of minimizing the cost of energy throughout the life cycle of the project. The obtained results show that assigning a value to the cost of blackouts can have a major impact on the economic viability of a resilient solution. For all cases the net present value of a system was always higher when a value was assigned to resilience. The values assigned to resilience were higher for users plugged to radial networks, which are more prone to blackouts, and lower for users connected to meshed grids, usually more reliable. Despite the fact that for the investigation presented here only three types of infrastructures were assessed, similar results could be expected for other critical infrastructures with similar loads and electricity tariffs. Resilient systems using photovoltaic solar installations that are limited in size could provide both economic savings during normal grid-connected operation and limited emergency power during blackouts. When these systems based on photovoltaic solar energy and electrochemical storage are used in conjunction with an emergency diesel generator, these resilient “hybrid” systems are capable of satisfying critical loads during short- and long-term blackouts.[ES] Un sistema fotovoltaico resiliente, que comprende el uso conjunto de paneles solares fotovoltaicos y un almacenamiento electroquímico que sea capaz de funcionar tanto con conexión a red como sin ella, es capaz de dar un servicio añadido tanto durante el funcionamiento normal conectado a red como cuando se produce un apagón ( a diferencia de un sistema solar tradicional). Cuando la red eléctrica convencional está en funcionamiento normal, los sistemas fotovoltaicos resilientes pueden generar ingresos y/o reducir la factura eléctrica. Durante los apagones, los sistemas fotovoltaicos resistentes son capaces de proporcionar energía de emergencia crítica para ayudar a respaldar los sistemas de generadores diésel. La investigación aquí presentada evalúa la viabilidad técnica y económica de sistemas basados en energía solar fotovoltaica y almacenamiento electroquímico en tres infraestructuras críticas que deben contar con un típico generador diésel de respaldo. Para ello, la investigación aquí presentada asigna un valor monetario al costo de evitar un apagón. Por lo tanto, el software REopt Lite se ha utilizado para seleccionar y dimensionar de manera óptima diferentes esquemas resilientes. Para cada uno de los casos evaluados los sistemas resilientes lograron obtener beneficios asociados a la sustitución del uso energético de la red eléctrica, la reducción de cargos por el uso de energía durante los períodos pico de energía y la modificación de los períodos de compra de energía de los períodos de alto costo a periodos de bajo costo. Para todos los casos el modelo encontró la combinación óptima de tecnologías capaces de minimizar el coste de la energía durante todo el ciclo de vida del proyecto. Los resultados obtenidos muestran que asignar un valor al costo de los apagones puede tener un impacto importante en la viabilidad económica de una solución resiliente. En todos los casos, el valor actual neto de un sistema siempre fue mayor cuando se asignó un valor a la resiliencia. Los valores asignados a la resiliencia fueron mayores para los usuarios conectados a redes radiales, que son más propensos a sufrir apagones, y menores para los usuarios conectados a redes malladas, generalmente más confiables. A pesar de que para la investigación aquí presentada sólo se evaluaron tres tipos de infraestructuras, se podrían esperar resultados similares para otras infraestructuras críticas con cargas y tarifas eléctricas similares. Los sistemas resilientes que utilizan instalaciones solares fotovoltaicas de tamaño limitado podrían proporcionar ahorros económicos durante el funcionamiento normal conectado a la red y energía de emergencia limitada durante los apagones. Cuando estos sistemas basados en energía solar fotovoltaica y almacenamiento electroquímico se utilizan junto con un generador diésel de emergencia, estos resistentes sistemas “híbridos” son capaces de satisfacer cargas críticas durante apagones de corto y largo plazo.S

Contribution of Driving Efficiency to Vehicle-to-Building

[EN] Energy consumption in the transport sector and buildings are of great concern. This research aims to quantify how eco-routing, eco-driving and eco-charging can increase the amount of energy available for vehicle-to-building. To do this, the working population was broken into social groups (freelancers, local workers and commuters) who reside in two cities with different climate zones (Alcalá de Henares-Spain and Jaén-Spain) since the way of using electric vehicles is different. An algorithm based on the Here® application program interface and neural networks was implemented to acquire data of the stochastic usage of EVs of each social group. Finally, an increase in the amount of energy available for vehicle-to-building was assessed thanks to the algorithm. The results per day were as follows. Owing to the algorithm proposed a reduction ranging from 0.6 kWh to 2.2 kWh was obtained depending on social groups. The proposed algorithm facilitated an increase in energy available for vehicle-to-building ranging from 13.2 kWh to 33.6 kWh depending on social groups. The results show that current charging policies are not compatible with all social groups and do not consider the renewable energy contribution to the total electricity demand.S

Teaching Using Collaborative Research Projects: Experiences with Adult Learners in Distance Education

[EN] This research studies the acquisition and improvement of specific cognitive, functional, and social competencies of the students enrolled in a university module in which we applied Collaborative Research Project (CRP) strategy. The module was Research Methodology for a master’s degree in research in electrical engineering, electronics and industrial control given at the National Distance Education University (UNED) in Spain. This practice was applied to a research project in which the private sector was interested in. We have been aiming at increasing academia–industry interaction while promoting active learning; both are principles advocated by the European Higher Education Area (EHEA). Having applied this strategy, the module learning outcomes were evaluated following the guideline standards set by the National Agency for Quality Assessment of Universities (ANECA) of the Spanish Government. The results from this evaluation indicated that CRP, even when carried out by using distance learning, has encouraged the students’ interest in both research and the module. It has also fostered collaboration between students and lecturers while increasing their degree of satisfaction. We highlight the difficulties in merging all the outcomes from the students’ research as the main drawback

An expert judgement approach to determine measures to remove institutional barriers and economic non-market failures that restrict photovoltaic self-consumption deployment in Spain

[EN] Despite the Spanish privileged geographical location and business leadership in the renewable energy field, currently is can be observed that the solar photovoltaic generation, electric self-consumption systems and net-metering policies deployment is much lower than it can be observed in other countries, even with lower energy sources for self-consumption. Energy policy experts assess as main reason the absence of a stable regulatory framework and the existence of clear disincentives. These disincentives are based on several economic non-market failures and institutional barriers. One key factor has proven to be the regulatory uncertainty created mainly by the recent national most relevant ministerial orders regarding energy generation and consumption, which suggests that, de facto, the regulatory framework is currently still under development. This paper includes first a brief but deep description of the prosumers penetration existing scenario in Spain, and then it focuses on feasible strategies to accelerate higher solar photovoltaic and self-consumption growth rates in Spain. Then, new policy measures to eliminate, or at least, mitigate, current barriers to their deployment are proposed and discussed. It is concluded that it results mandatory the urgent modernization of the energy regulatory framework promoting an active role for distributed PV generation which could have a significant positive impact in the voltage control and frequency regulation in distribution networks, among other advantages.[ES] A pesar de la privilegiada situación geográfica española y del liderazgo empresarial en el campo de las energías renovables, en la actualidad se observa que el despliegue de la generación solar fotovoltaica, de los sistemas de autoconsumo eléctrico y de las políticas de net-metering es muy inferior al que se observa en otros países, incluso con menores fuentes de energía para el autoconsumo. Los expertos en política energética valoran como razón principal la ausencia de un marco regulatorio estable y la existencia de claros desincentivos. Estos desincentivos se basan en varios fallos económicos ajenos al mercado y en barreras institucionales. Un factor clave ha resultado ser la incertidumbre regulatoria creada principalmente por las recientes órdenes ministeriales nacionales más relevantes en materia de generación y consumo de energía, lo que sugiere que, de facto, el marco regulador se encuentra actualmente en fase de desarrollo. Este trabajo incluye en primer lugar una breve pero profunda descripción del escenario de penetración de prosumidores existente en España, y a continuación se centra en las estrategias viables para acelerar mayores tasas de crecimiento de la energía solar fotovoltaica y el autoconsumo en España. A continuación, se proponen y discuten nuevas medidas políticas para eliminar, o al menos, mitigar, las barreras actuales a su despliegue. Se concluye que resulta obligatoria la urgente modernización del marco regulatorio energético promoviendo un papel activo para la generación fotovoltaica distribuida que podría tener un impacto positivo significativo en el control de la tensión y la regulación de la frecuencia en las redes de distribución.S

Battery energy storage performance in microgrids: A scientific mapping perspective

[EN] Microgrids integrate various renewable resources, such as photovoltaic and wind energy, and battery energy storage systems. The latter is an important component of a modern energy system, as it allows the seamless integration of renewable energy sources in the grid. The research here presented aimed to develop an integrated review using a systematic and bibliometric approach to evaluate the performance and challenges in applying battery energy storage systems in microgrids. Search protocols based on a literature review were used; this included thematic visualization and performance analysis using the scientific mapping software SciMAT (Science Mapping Analysis Software Tool). The results show that optimization methods in battery energy storage systems are important for this research field. In research works, they are interested in applying methods to reduce costs; this includes considering the state of charge, the degradation rate, and battery life. Developing an optimal battery energy storage system must consider various factors including reliability, battery technology, power quality, frequency variations, and environmental conditions. Economic factors are the most common challenges for developing a battery energy storage system, as researchers have focused on cost–benefit analysis.S

Optimized design method for storage systems in photovoltaic plants with delivery limitation

Versión aceptada para publicación. No contiene los cambios menores recogidos tras el proof reading.[EN] It results widely common for distribution network operators to impose restrictions on delivered solar photovoltaic generated power when the power plant rated power is greater than the maximum allowed due to the distribution network capacity. Thus, a feasible solution to maximize the performance of the solar power plant is the integration of battery energy storage systems. Although this configuration has been extensively studied in the existing literature, an optimal design method to determine the proper size and operation of the energy storage system needs to be developed. In this paper, a novel method to help power plants designers to determine the optimal battery energy storage capacity to integrate into any solar photovoltaic power plant is provided. The proposed algorithm minimizes the potential power curtailment and optimizes the utilization rate of the batteries storage system. The algorithm can be applied to any grid connected solar photovoltaic power plant under delivery power restrictions, regardless of power capacity and location. The algorithm has been implemented to a simulated power plant with delivery limitations based in a real case, and results with the optimal battery capacity show that the system would be able to recover up to the 83% of the curtailed energy and a yearly average capacity utilization of 56%. Moreover, the BESS operation has been validated with a scaled model run in Simulink and laboratory measurements, achieving 98% of curtailed energy recovery rate and a 57% of average capacity utilization.[ES] Resulta muy habitual que los operadores de las redes de distribución impongan restricciones a la potencia generada por energía solar fotovoltaica suministrada cuando la potencia nominal de la central es superior a la máxima permitida debido a la capacidad de la red de distribución. Por ello, una solución factible para maximizar el rendimiento de la central solar es la integración de sistemas de almacenamiento de energía en baterías. Aunque esta configuración ha sido ampliamente estudiada en la literatura existente, es necesario desarrollar un método de diseño óptimo para determinar el tamaño y funcionamiento adecuados del sistema de almacenamiento de energía. En este trabajo se presenta un método novedoso para ayudar a los diseñadores de centrales eléctricas a determinar la capacidad óptima de almacenamiento de energía en baterías para integrar en cualquier central solar fotovoltaica. El algoritmo propuesto minimiza el posible recorte de potencia y optimiza la tasa de utilización del sistema de almacenamiento en baterías. El algoritmo puede aplicarse a cualquier planta de energía solar fotovoltaica conectada a la red bajo restricciones de potencia de entrega, independientemente de la capacidad de potencia y la ubicación. El algoritmo se ha aplicado a una central eléctrica simulada con limitaciones de suministro basada en un caso real, y los resultados con la capacidad óptima de las baterías muestran que el sistema sería capaz de recuperar hasta el 83% de la energía restringida y una utilización media anual de la capacidad del 56%. Además, el funcionamiento del BESS se ha validado con un modelo a escala ejecutado en Simulink y mediciones de laboratorio, y se ha conseguido recuperar el 98% de la energía restringida.S

A method of determining the thermal power demand of buildings connected to the district heating system with usage of heat accumulation

The paper presents a new method of determining the thermal power demand of buildings connected to the district heating system, which included the actual heat demand and the possibility of balancing the thermal power using the thermal storage capacity of district heating network and internal heat capacity of buildings. Moreover, the analysis of the effect of incidence of external air temperature and duration of episodes with the lowest outdoor temperatures on the thermal power demand of district heating system was conducted

Microgrids with energy storage systems as a means to increase power resilience: An application to office buildings

[EN] This work describes a methodology to quantify the benefits from both a business-related and energy resilience perspectives provided by a microgrid based on photovoltaic solar energy and electrochemical energy storage integrated in large buildings, such as office buildings not open to the general public, which is presented as case study. First it has been identified how, by using distributed renewable energy sources (in particular, photovoltaic solar energy) and electrochemical energy storage systems, the life-cycle cost of the energy in a microgrid connected to the electrical network can be reduced significantly. As novel approach, it has been evaluated how this microgrid design can increase the resilience of a power customer supply, quantified as the time period the microgrid is able to feed an electrical consumer at an outage, which it results of great importance for large office buildings that are used to have several critical loads, such as data servers and data processing centers. It was found that, by adding photovoltaic solar energy and electrochemical storage, it is possible to extend the power resilience of this sort of power customers achieving an average survival time to a power cut of 4 h thanks to the proposed solar photovoltaic and energy storage system. Then, the microgrid could save $112,410 in energy over the 20-year life cycle of the facility, while increasing the amount of time it can survive a power outage. The proposed methodology presented in this paper provides a model that can be applied to other case studies and scenarios where an alternative to the classic diesel-based emergency supply systems are needed.[ES] Este trabajo describe una metodología para cuantificar los beneficios, tanto desde el punto de vista empresarial como de la resiliencia energética, que proporciona una microrred basada en energía solar fotovoltaica y almacenamiento electroquímico de energía integrada en grandes edificios, como edificios de oficinas no abiertos al público en general, que se presenta como caso de estudio. En primer lugar se ha identificado cómo, mediante el uso de fuentes de energía renovables distribuidas (en particular, energía solar fotovoltaica) y sistemas de almacenamiento electroquímico de energía, se puede reducir significativamente el coste del ciclo de vida de la energía en una microrred conectada a la red eléctrica. Como enfoque novedoso, se ha evaluado cómo este diseño de microrred puede aumentar la resiliencia del suministro de un cliente eléctrico, cuantificada como el periodo de tiempo que la microrred es capaz de alimentar a un consumidor eléctrico ante un corte, lo que resulta de gran importancia para grandes edificios de oficinas que suelen tener varias cargas críticas, como servidores de datos y centros de proceso de datos. Se comprobó que, añadiendo energía solar fotovoltaica y almacenamiento electroquímico, es posible ampliar la resiliencia energética de este tipo de clientes eléctricos logrando un tiempo medio de supervivencia a un corte de suministro de 4 h gracias al sistema solar fotovoltaico y de almacenamiento de energía propuesto. Así, la microrred podría ahorrar 112.410$ en energía durante los 20 años de vida útil de la instalación, a la vez que aumenta el tiempo de supervivencia a un corte de suministro. La metodología propuesta en este documento proporciona un modelo que puede aplicarse a otros casos de estudio y escenarios donde se precisen alternativas a los sistemas clásicos basados en sistemas diésel para el suministro de emergencia.S

An accurate model for simulating energetic behavior of PV grid connected inverters

This paper proposes a new model for characterizing the energetic behavior of grid connected PV inverters. The model has been obtained from a detailed study of main loss processes in small size PV inverters in the market. The main advantage of the used method is to obtain a model that comprises two antagonistic features, since both are simple, easy to compute and apply, and accurate. One of the main features of this model is how it handles the maximum power point tracking (MPPT) and the efficiency: in both parts the model uses the same approach and it is achieved by two resistive elements which simulate the losses inherent to each parameter. This makes this model easy to implement, compact and refined. The model presented here also includes other parameters, such as start threshold, standby consumption and islanding behavior. In order to validate the model, the values of all the parameters listed above have been obtained and adjusted using field measurements for several commercial inverters, and the behavior of the model applied to a particular inverter has been compared with real data under different working conditions, taken from a facility located in Madrid. The results show a good fit between the model values and the real data. As an example, the model has been implemented in PSPICE electronic simulator, and this approach has been used to teach grid-connected PV systems. The use of this model for the maintenance of working PV facilities is also shown

Annelid Borings on Brachiopod Shells From the Upper Ordovician of Peru. A Long-Distance Co-migration of Biotic Partners

The Recent planktonic larvae of the polychaete spionids are some of the most widespread and abundant group of coastal meroplankton worldwide. To study the possible co-migration of biotic partners and determine whether they were host-specific, the type of biotic relationship between hosts and borers of an Upper Ordovician Peruvian brachiopod collection from the Proto-Andean margin of Gondwana was re-exanimated and compared with material from Wales (Avalonia). The species list studied is composed of Colaptomena expansa (41%), Heterorthis retrorsistria (24%), Horderleyella chacaltanai (19%), Drabovinella minuscula (13%), and Dinorthis cf. flabellulum (3%) and coincides closely with that of the Dinorthis community described in the Caradoc series of North Wales. The borings attributed to these spionids have been identified as Palaeosabella prisca only present in the valves of Colaptomena expansa and Heterorthis retrorsistria. All the studied valves are disarticulated, with very low fragmentation and are randomly oriented in a context below the fair-weather wave base. The settling larvae would feed on their brachiopod host soft parts at an early stage, being the biotic interaction initially of the parasitic type. Since Palaeosabella borings from Peru and Wales are identical, as well as the species specificity of their producers with their brachiopod hosts, it can be concluded that the same spionid annelid species produced them. The Southern Westerlies current that connected the Proto-Andean margin of Gondwana with Avalonia must have been responsible for transporting the larvae of annelids and brachiopods in what had to be a successful biotic relationship over a great transoceanic distance