Power systems with high renewable energy sources: A review of inertia and frequency control strategies over time

Traditionally, inertia in power systems has been determined by considering all the rotating masses directly connected to the grid. During the last decade, the integration of renewable energy sources, mainly photovoltaic installations and wind power plants, has led to a significant dynamic characteristic change in power systems. This change is mainly due to the fact that most renewables have power electronics at the grid interface. The overall impact on stability and reliability analysis of power systems is very significant. The power systems become more dynamic and require a new set of strategies modifying traditional generation control algorithms. Indeed, renewable generation units are decoupled from the grid by electronic converters, decreasing the overall inertia of the grid. ‘Hidden inertia’, ‘synthetic inertia’ or ‘virtual inertia’ are terms currently used to represent artificial inertia created by converter control of the renewable sources. Alternative spinning reserves are then needed in the new power system with high penetration renewables, where the lack of rotating masses directly connected to the grid must be emulated to maintain an acceptable power system reliability. This paper reviews the inertia concept in terms of values and their evolution in the last decades, as well as the damping factor values. A comparison of the rotational grid inertia for traditional and current averaged generation mix scenarios is also carried out. In addition, an extensive discussion on wind and photovoltaic power plants and their contributions to inertia in terms of frequency control strategies is included in the paper.This work was supported by the Spanish Education, Culture and Sports Ministry [FPU16/04282]

Frequency control studies: A review of power system, conventional and renewable generation unit modeling

Over the last decades, renewable energy sources have increased considerably their generation share in power systems. As a consequence, in terms of frequency deviations, both grid reliability and stability have raised interest. By considering the absence of a consensual set of models for frequency control analysis, both for the different generation units (conventional and renewables) and the power system itself, this paper provides extensive and significant information focused on the models and parameters for studies about frequency control and grid stability. An extensive analysis of supply-side and power system modeling for frequency stability studies over the last decade is presented and reviewed. Parameters commonly used and assumed in the specific literature for such simulations are also given and compared. Modeling of generation units are described as well, including both conventional and renewable power plants.The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper

Graphene-derived materials as oxygen reduction catalysts in alkaline conditions for energy applications

Graphene is a relatively new carbon material increasingly finding technological applications due to its unique physical and engineering properties. Here, its application as catalyst for the oxygen reduction reaction (ORR) in alkaline media is investigated. First, the role of graphene-related materials (including multi-walled carbon nanotubes) as catalyst supports is compared to the widely used carbon black, finding that the ORR follows a mixed behaviour between the direct 4-electron pathway and the indirect 2-step mechanism on graphene-supported platinum catalysts. Further, different combinations of boron, nitrogen, phosphorus and sulphur metal-free doped-graphene catalysts have been systematically synthesised and evaluated, finding that dual-doped graphene catalysts yield the best ORR performance. Specifically, phosphorus and nitrogen dual-doped graphene (PN-Gr) demonstrates the highest catalytic activity, with 3.5 electrons transferred during the ORR. Doped-graphene/perovskite oxide hybrid catalysts have been also tested, yielding PN-Gr/La0.8Sr0.2MnO3 the best ORR activity in terms of measured current density, achieving a value that is 85% of that reported for a commercial Pt/C catalyst. Moreover, SN-Gr/La0.8Sr0.2MnO3 produces the lowest amount of peroxide formation with only 10%. These results confirm the graphene-derived catalysts as promising alternatives to the current platinum-based catalysts, and could enable the important issues related to its practical application to be overcome

Novel fishnet-like chiral metamaterial structure with negative refractive index and low losses

In this work a composed chiral metamaterial structure constituted by the combination of a composite chiral metamaterial and a modified fishnet structure is presented and numerically analyzed. This new fishnet-like chiral metamaterial features two wide frequency bands wherein the refractive indices are negative and exhibits lower losses than its constituents do.This work has been partially supported by the Spanish Government MINECO through the ERDF co-funded Research Projects TEC2014-55463-C3-1-P and TEC2014-55463-C3-3-P

Assessment and simulation of the responsive demand potential in end-user facilities: application to a university customer

Many problems have appeared with the practical implementation of restructured electrical business in the U.S.and European Union such as lack of generation,network constraints,etc. A good example of these problems is the scarce participation of the demand in the electricity markets—energy,reserve,and other ancillary services—problems that could be solved through new de-mand responsive programs,aimed to replace the traditional demand side management programs in to voluntary demand partici-pation programs.A methodology for the generation of demand side bids and ofers in large customer facilities and a real application to a university customer is presented in this paper.The methodology is based on the knowledge of the physical processes involved in the electricity consumption and on the flexibility of there quired supply.The result of the methodology proposed is a set of demand packages that can be used to participate in different electricity markets,whose possibilities- in the market arena — will be explored in a consequent paper.This work was supported by the Ministerio de Ciencia y Tecnología of Spain through Research Project DPI2001-2779-C02-01

Vertical wind profile characterization and identification of patterns based on a shape clustering algorithm

Wind power plants are becoming a generally accepted resource in the generation mix of many utilities. At the same time, the size and the power rating of individual wind turbines have increased considerably. Under these circumstances, the sector is increasingly demanding an accurate characterization of vertical wind speed profiles to estimate properly the incoming wind speed at the rotor swept area and, consequently, assess the potential for a wind power plant site. The present paper describes a shape-based clustering characterization and visualization of real vertical wind speed data. The proposed solution allows us to identify the most likely vertical wind speed patterns for a specific location based on real wind speed measurements. Moreover, this clustering approach also provides characterization and classification of such vertical wind profiles. This solution is highly suitable for a large amount of data collected by remote sensing equipment, where wind speed values at different heights within the rotor swept area are available for subsequent analysis. The methodology is based on z-normalization, shape-based distance metric solution and the Ward-hierarchical clustering method. Real vertical wind speed profile data corresponding to a Spanish wind power plant and collected by using a commercialWindcube equipment during several months are used to assess the proposed characterization and clustering process, involving more than 100000 wind speed data values. All analyses have been implemented using open-source R-software. From the results, at least four different vertical wind speed patterns are identified to characterize properly over 90% of the collected wind speed data along the day. Therefore, alternative analytical function criteria should be subsequently proposed for vertical wind speed characterization purposes.The authors are grateful for the financial support from the Spanish Ministry of the Economy and Competitiveness and the European Union —ENE2016-78214-C2-2-R—and the Spanish Education, Culture and Sport Ministry —FPU16/042

Chiral metamaterial structure with high optical activity based on conjugated omega particles

In this communication the authors present a novel chiral metamaterial structure formed by planar omega particles These omega particles, arranged in conjugated pairs, present high optical activity. Thanks to the high values of chirality, the structure provides negative refractive index with high figure of merit.This work has been supported by the Spanish Government MINECO through the Research Projects TEC2014-55463-C3-1-P, TEC2014-55463-C3-3-P and by the European Commission (ERDF)

Reject brine management: Denitrification and zero liquid discharge (ZLD)—Current status, challenges and future prospects

Water is at the core of sustainable development. Moreover, it is essential for social, economic, and environmental well-being. However, water resource availability has been significantly threatened in the 21st century. In general, freshwater supplies are being depleted by natural and anthropogenic activities, such as rapid population growth, industrialization, and intensive agriculture. In addition, one of the main causes of water resource shortages is water body contamination. Nitrate pollution is considered one of the most pressing global environmental problems, both in surface and groundwater. The literature reveals that numerous nitrogen removal processes have been developed and proposed. To overcome this problem, desalination is a robust and mature technique for obtaining fresh water from saltwater, and is considered an efficient and reliable process. However, there is growing concern about the adverse environmental impacts generated by brine where concentrated rejection by desalination results in high salinity together with chemical residues. To solve this problem, a zero liquid discharge (ZLD) strategy has been proposed in the specific literature. Furthermore, ZLD can be used to treat and recover valuable resources. This study analyzes and discusses the current status of brine treatment technologies targeting ZLD, highlighting their advantages and disadvantages. Technologies based on membranes and thermal energy were also analyzed, and their performance and operating costs were compared. Finally, the different denitrification processes are listed. This ZLD solution is currently considered an essential and compulsory treatment in reject brine to remove nitrate that, because of high concentrations in the environment, is one of the most widespread global contaminants.This work was financially supported by the Life+ European Project (LIFE19 ENV/ES/00447)

Optimal integration modeling of Co–Electrolysis in a power-to-liquid industrial process

High temperature co-electrolysis using solid-oxide electrolysis cells is a highly efficient pathway for green syngas production owing to the possibility of heat integration with other processes. Therefore, this study described and evaluates a flexible and efficient configuration for producing sustainable synthetic fuels using electricity from renewables and captured CO2 by integrating co-electrolysis in a power-to-liquid industrial plant. Thereafter, novel and efficient technologies were implemented for green syngas production and its subsequent purification, increasing the overall process efficiency and achieving a significant reduction in the carbon footprint compared to mature synthetic crude production processes. Catalytic partial oxidation and dual pressure swing adsorption were integrated with co-electrolysis and Fischer–Tropsch synthesis in a scaled industrial plant, using residual streams from the complex or those of renewable origin as feed, which allowed the continuous operation of the process independent of renewable power generation. The mass and energy balance, performance, and efficiency estimations were also included in this study. A solid-oxide electrolytic cell (SOEC) plant using renewable electricity and heat input from thermal integration with the outlet syngas stream of the catalytic partial oxidation reactor was selected as a case study. Both the performance and efficiency analyses of the co-electrolysis unit demonstrated the benefits of such thermal integration in comparison with current solutions. In this study, both the thermal integration of the process streams, as well as the energy and heat consumed by the syngas purification process were considered.The authors acknowledge the project funded by the Comunidad Autónoma de la Región de Murcia, Consejería de Desarrollo Económico, Turismo y Empleo (Región de Murcia, Spain), and the European Union through the program RIS3MUR (Ref:2I20SAE00079)

Analysis and comparison of energy efficiency code requirements for buildings: A Morocco–Spain case study

The trend in energy consumption, with a particular focus on heating and cooling demand, is an issue that is relevant to the promotion of new energy policies and more efficient energy systems. Moreover, heating and cooling energy demand is expected to rise in the next several decades, mainly due to climate change as well as increasing incomes in developing countries. In this context, the building sector is currently a relevant energy-intensive economic sector in Morocco; it accounts for 33% of the country’s total energy demand (as the sector with the second highest energy demand, after the transport sector), with the residential sector accounting for 25% and the tertiary sector accounting for 8%. Aiming to reduce energy dependence and promote sustainable development, the Moroccan government recently issued a comprehensive plan to increase the share of renewables and improve energy efficiency. This strategy includes novel thermal building regulations promoted by the Moroccan Agency for Energy Efficiency. This paper analyzes the thermal behavior and heating-cooling energy demand of a residential building located in Tangier (Morocco) as a case example, based on the country’s new thermal regulations and considering specific climatological conditions. A comparison with common Moroccan residential buildings as well as with those in nearby countries with similar meteorological conditions but significant differences in terms of energy demand regulation and requirements, such as Spain, is also included. Simulations were carried out using the DesingBuilder and EnergyPlus Software packages. According to the results, the last building thermal regulation requirements in Morocco need to be revised and extended in order to achieve the energy efficiency objectives established by the Moroccan government for 2030