A review on economic and technical operation of active distribution systems

© 2019 Elsevier Ltd Along with the advent of restructuring in power systems, considerable integration of renewable energy resources has motivated the transition of traditional distribution networks (DNs) toward new active ones. In the meanwhile, rapid technology advances have provided great potentials for future bulk utilization of generation units as well as the energy storage (ES) systems in the distribution section. This paper aims to present a comprehensive review of recent advancements in the operation of active distribution systems (ADSs) from the viewpoint of operational time-hierarchy. To be more specific, this time-hierarchy consists of two stages, and at the first stage of this time-hierarchy, four major economic factors, by which the operation of traditional passive DNs is evolved to new active DNs, are described. Then the second stage of the time-hierarchy refers to technical management and power quality correction of ADSs in terms of static, dynamic and transient periods. In the end, some required modeling and control developments for the optimal operation of ADSs are discussed. As opposed to previous review papers, potential applications of devices in the ADS are investigated considering their operational time-intervals. Since some of the compensating devices, storage units and generating sources may have different applications regarding the time scale of their utilization, this paper considers real scenario system operations in which components of the network are firstly scheduled for the specified period ahead; then their deviations of operating status from reference points are modified during three time-intervals covering static, dynamic and transient periods

Benchmarking renewable energy sources carbon savings and economic effectiveness

Over the last decade, the levelised cost of energy (LCOE) of many renewable technologies has sharply declined. As a result, direct cost comparisons of LCOE figures have made renewables to be perceived as economically very competitive options to decarbonise energy systems when compared to other low-carbon technologies such as Nuclear and Carbon Capture and Storage. We identify several theoretical shortcomings in relation to using LCOE or similar life-cycle economic metrics to make inferences about the relative economic effectiveness of using renewable technologies to decarbonise energy systems. We outline several circumstances in which the sole reliance on these metrics can lead to suboptimal or misguided investment and policymaking decisions. The thesis proposes a new theoretical framework to measure and benchmark the cost- effectiveness of decarbonising electric systems using renewables. The new framework is generic, technology-neutral, and enables consolidation of the results of decarbonisation studies that consider various renewable technologies and low carbon technologies. It also enables measuring and tracking the cost-effectiveness of the renewable decarbonisation process at a country or a system level. As a result, it also allows the direct comparison of the economic implications of different decarbonisation scenarios and various policy proposals in a very intuitive graphical way. In addition, the thesis proposes a new, unit-free metric, tentatively called Carbon Economic Effectiveness Credit (CEEC), to benchmark the relative cost-effectiveness of using different renewable technologies to achieve long-term carbon emission savings. Theoretically, CEEC represents the elasticity of the system total cost with respect to the carbon reduction savings attributable to renewables. In contrast to stand-alone, life-cycle metrics such as the LCOE, the proposed metric considers the economic and technical parameters of the renewable technologies and characteristic of the system under study. It also allows expressing the cost- effectiveness of the renewable decarbonisation process as a function of the system-wide decarbonisation level. Using historical load profiles, high-resolution solar radiation data and long-term meteorological data for a relatively small Gulf country, we investigate the deep decarbonisation of the electric system through the large-scale deployment of different renewables technologies. In particular, we use two well-established optimisation methodologies that have been used extensively in the literature to study the decarbonisation of power systems, namely: the screening curve (SC) method and the unit commitment (UC) method. In analysing the results of the two methodologies, we find that the choice of the modelling methodology, in some cases, can greatly influence the perceived carbon cost- effectiveness of renewables and subsequently their carbon abatement cost estimates. In particular, our results suggest that under deep decarbonisation scenarios, the estimate of the long-term carbon savings of renewables is strongly influenced by (1) the choice of the modelling method and (2) the technical specifications of the simulation models. Our results suggest that under deep decarbonisation scenarios, using simpler optimisation models may change the perceived economic effectiveness of renewables to decarbonise some electric systems. More importantly, our research sheds light on potential shortcomings in the current modelling practices and help identify patterns of possible inaccuracies or biases in renewable decarbonisation results. Moreover, our research suggests that the variations in the technical characteristics of renewable technologies can have a large influence on the economics of the decarbonisation process. We show that not all renewable technology types can have a suppressing effect on the variable costs of the systems due to their “zero marginal costs.” In particular, we identify certain technologies and circumstances in which an increase in renewable penetration can significantly inflate the variable energy costs of the system. More specifically, we find that under deep decarbonisation scenarios, renewable technologies with a highly volatile production profiles can act as an amplifier for the variable cost of the systems through (1) reducing the effectiveness of thermal generation units due the increased start-up and shutting downing activities, and (2) increasing the energy output levels from more flexible and yet more expensive thermal technologies. In addition, we identify circumstances in which an increased renewable penetration can materially affect the capacity adequacy of electric systems, leading to an increase in capacity investment in thermal flexibility assets. Perhaps more importantly, we find that these additional flexibility assets will not be commercially viable on an energy-output basis. We believe that this might have specific implications for the energy-only markets. Finally, we discuss the policy implications of our findings and propose several important recommendations. Altogether, we hope that our work will advance the understanding of the economics of climate change and integrating renewables into energy systems.Open Acces

Energy storage systems and grid code requirements for large-scale renewables integration in insular grids

This thesis addresses the topic of energy storage systems supporting increased penetration of renewables in insular systems. An overview of energy storage management, forecasting tools and demand side solutions is carried out, comparing the strategic utilization of storage and other competing strategies. Particular emphasis is given to energy storage systems on islands, as a new contribution to earlier studies, addressing their particular requirements, the most appropriate technologies and existing operating projects throughout the world. Several real-world case studies are presented and discussed in detail. Lead-acid battery design parameters are assessed for energy storage applications on insular grids, comparing different battery models. The wind curtailment mitigation effect by means of energy storage resources is also explored. Grid code requirements for large-scale integration of renewables are discussed in an island context, as another new contribution to earlier studies. The current trends on grid code formulation, towards an improved integration of distributed renewable resources in island systems, are addressed. Finally, modeling and control strategies with energy storage systems are addressed. An innovative energy management technique to be used in the day-ahead scheduling of insular systems with Vanadium Redox Flow battery is presented.Esta tese aborda a temática dos sistemas de armazenamento de energia visando o aumento da penetração de energias renováveis em sistemas insulares. Uma visão geral é apresentada acerca da gestão do armazenamento de energia, ferramentas de previsão e soluções do lado da procura de energia, comparando a utilização estratégica do armazenamento e outras estratégias concorrentes. É dada ênfase aos sistemas de armazenamento de energia em ilhas, como uma nova contribuição no estado da arte, abordando as suas necessidades específicas, as tecnologias mais adequadas e os projetos existentes e em funcionamento a nível mundial. Vários casos de estudos reais são apresentados e discutidos em detalhe. Parâmetros de projeto de baterias de chumbo-ácido são avaliados para aplicações de armazenamento de energia em redes insulares, comparando diferentes modelos de baterias. O efeito de redução do potencial de desperdício de energia do vento, recorrendo ao armazenamento de energia, também é perscrutado. As especificidades subjacentes aos códigos de rede para a integração em larga escala de energias renováveis são discutidas em contexto insular, sendo outra nova contribuição no estado da arte. As tendências atuais na elaboração de códigos de rede, no sentido de uma melhor integração da geração distribuída renovável em sistemas insulares, são abordadas. Finalmente, é estudada a modelação e as estratégias de controlo com sistemas de armazenamento de energia. Uma metodologia de gestão de energia inovadora é apresentada para a exploração de curto prazo de sistemas insulares com baterias de fluxo Vanádio Redox

Wind Power Cogeneration to Reduce Peak Electricity Demand in Mexican States Along the Gulf of Mexico

The Energetic Transition Law in Mexico has established that in the next years, the country has to produce at least 35% of its energy from clean sources in 2024. Based on this, a proposal in this study is the cogeneration between the principal thermal power plants along the Mexican states of the Gulf of Mexico with modeled wind farms near to these thermal plants with the objective to reduce peak electricity demand. These microscale models were done with hourly MERRA-2 data that included wind speed, wind direction, temperature, and atmospheric pressure with records from 1980–2018 and taking into account roughness, orography, and climatology of the site. Wind speed daily profile for each model was compared to electricity demand trajectory, and it was seen that wind speed has a peak at the same time. The amount of power delivered to the electric grid with this cogeneration in Rio Bravo and Altamira (Northeast region) is 2657.02 MW and for Tuxpan and Dos Bocas from the Eastern region is 3196.18 MW. This implies a reduction at the peak demand. In the Northeast region, the power demand at the peak is 8000 MW, and for Eastern region 7200 MW. If wind farms and thermal power plants work at the same time in Northeast and Eastern regions, the amount of power delivered by other sources of energy at this moment will be 5342.98 MW and 4003.82 MW, respectively

Renewable Electricity Futures Study. Volume 4: Bulk Electric Power Systems: Operations and Transmission Planning

The Renewable Electricity Futures (RE Futures) Study investigated the challenges and impacts of achieving very high renewable electricity generation levels in the contiguous United States by 2050. The analysis focused on the sufficiency of the geographically diverse U.S. renewable resources to meet electricity demand over future decades, the hourly operational characteristics of the U.S. grid with high levels of variable wind and solar generation, and the potential implications of deploying high levels of renewables in the future. RE Futures focused on technical aspects of high penetration of renewable electricity; it did not focus on how to achieve such a future through policy or other measures. Given the inherent uncertainties involved with analyzing alternative long-term energy futures as well as the multiple pathways that might be taken to achieve higher levels of renewable electricity supply, RE Futures explored a range of scenarios to investigate and compare the impacts of renewable electricity penetration levels (30%-90%), future technology performance improvements, potential constraints to renewable electricity development, and future electricity demand growth assumptions. RE Futures was led by the National Renewable Energy Laboratory (NREL) and the Massachusetts Institute of Technology (MIT)

Integration of Renewables in Power Systems by Multi-Energy System Interaction

This book focuses on the interaction between different energy vectors, that is, between electrical, thermal, gas, and transportation systems, with the purpose of optimizing the planning and operation of future energy systems. More and more renewable energy is integrated into the electrical system, and to optimize its usage and ensure that its full production can be hosted and utilized, the power system has to be controlled in a more flexible manner. In order not to overload the electrical distribution grids, the new large loads have to be controlled using demand response, perchance through a hierarchical control set-up where some controls are dependent on price signals from the spot and balancing markets. In addition, by performing local real-time control and coordination based on local voltage or system frequency measurements, the grid hosting limits are not violated

Accommodation capacity evaluation of renewable energy in power systems considering peak and frequency regulation

With the fast growth of renewable energy, the modern power systems are transitioning to the renewable energy dominated energy systems. However, the intrinsic intermittence and volatility of renewable energy also impose considerable challenges on the power system operation. Hence, it is of great significance to accurately evaluate the renewable energy accommodation capacity (REAC) in power system so as to effectively instruct the sustainable development of renewable energy and to alleviate the ongoing operational burdens. This paper proposes a novel evaluation method of REAC in power system comprehensively considering peak and frequency regulation. First, the mechanism and cost of deep peak regulation of thermal power units are deeply analyzed, and then the frequency dynamics response is modeled explicitly and simplified effectively. Next, a synthetic interaction model of “source-network-storage” is developed with diversified generation units, network and energy storage constraints. Furthermore, a multi-objective optimization model is established considering both economic and technical issues, and a REAC evaluation method is developed by integrating an incremental capacity augment approach with the proposed multi-objective model. Finally, the proposed REAC evaluation method is tested on the modified IEEE 39-bus system, and the numerical results verify the effectiveness of the proposed method