National Electric System Research Articles

ANALYSIS OF A BRAZILIAN THERMAL PLANT OPERATION APPLYING ENERGETIC AND EXERGETIC BALANCES

ABSTRACT When the level of water reservoirs from Brazilian hydroelectric stations is low, additional thermal plants are turned on to complement the power of the national electric system. The fuels used in these plants are generally natural gas, fuel oil and coal. The objective of this work is to analyze energetically and exergetically a fuel oil thermal plant in operation in Brazil. Real industrial data were used in this analysis. The calculated total work of the turbine is 120.73 MW, which is close to the real value of 120 MW. The cycle energetic efficiency is 36.8% and the exergetic efficiency is 34.4%. The highest exergy destruction was found to be in the boiler (177.11 MW), followed by the high pressure turbine (13.37 MW), due to larger irreversibilities in the processes of these equipment. The exergetic analysis functioned as a complement to the energetic analysis, pointing out where the greatest irreversibilities and improvement potential are: in the boiler.

The concept of use of PV/WT/FC hybrid power generation system for smoothing the energy profile of the consumer

The rapid growth of stochastic sources of renewable sources has caused crowding out of conventional units from work at the basic to peak hours and intermediate. The increase in the failure frequency of steam blocks is connected among others with the change of their function in the electrical power engineering system saturated with sources at stochastic character of the work. While planning load distribution between conventional and unconventional sources, environmental and economic issues cannot only be taken into consideration. This problem should be dealt with in a comprehensive way. Technical - economic aspects of work of sources at stochastic nature of work as well as the aspects of work of the entire power system must be included.The article describes a mathematical model that allows to carry out a multi-criteria comparative analysis of collaboration scenarios of hybrid power generation system with the national electricity system based on the conventional energy sources.The model defines four evaluation criteria of considered scenarios: additional fuel usage by hybrid power generation system, the unit cost of electricity generation by the hybrid power generation system, the emission of carbon dioxide during work and the degree of capacity utilization of power ordered by the consumer.

Analysis of the Topologies of Power Filters Applied in Distributed Generation Units - Review

Considering the current scenario of the advance of the use of renewable energy sources, mainly wind and solar photovoltaic, in the Brazilian energy matrix. At the same time, there is concern about the stability of the power system and its respective power quality (PQ), due to this type of generation of non-linear loads, such as current converters, which in turn cause distortion Of the current and voltage waveform. The generation of energy by renewable sources does not participate in the control of the voltage and frequency of the electrical system, and in the occurrence of disturbances that exceed the pre-established limits and that affect the system's PQ, are disconnected until the PQ is restored, to be Reconnected after normal operation returns. In order to standardize and quantify the electromagnetic disturbances of the QEE, as well as ensure the quality of the product and services, standards and procedures were designed to instruct from generators to energy consumers. In Brazil, the Electric Power Distribution Procedure in the National Electric System (PRODIST) - module 8. The disturbances of the PQ in the generating units, mainly wind and solar photovoltaic are caused by the harmonics of current, generated by the converters, causing the distortion in the waveform, which in turn, increases the losses in transformers and transmission lines, reduction of cable and equipment life, flicker. Among the possible techniques to minimize the effects of harmonics, the use of passive, active and hybrid filters stands out. However the applicability of each type of filter depends on each system where it will be applied according to the characteristics of the electrical system. Thus, in order to contribute to the advancement of the topic, it can be observed that the use of power filters has a good functionality in harmonic attenuation as well as economical solution. Therefore, this work presents a mapping of the main technologies and methodologies for the design of power filters that can be customized for the mitigation of harmonic disturbances and improvement of the power factor. Finally, it presents a comparative analysis between the topologies of power filters, followed by an alternative proposal of an automated filter for microgeneration of energy connected in low voltage.

Will the integration of renewable energy enable sustainable transition of Indian electricity system?

Electricity systems worldwide are transitioning from conventional carbon intensive firm power generating systems to intermittent and variable renewable energy dominated low carbon systems. Although the dimensions of transition vary from one electricity system to another, there is concurrence in terms of need for and the subsequent issues related to renewable energy integration. In this study, we attempt to verify whether these transitions lead to a sustainable electricity system as measured through three dimensions – economic, social and environmental. This is performed by adopting an integrated framework, which connects the indicator based multi-hierarchical and multidimensional macro model of electricity system sustainability assessment with the bottom up optimization model of generation expansion planning and generation scheduling. We explore multiple scenarios and characterize Indian electricity system on select indicators under three sustainability dimensions. We aggregate this annual characterization to compute National Electricity System Sustainability Index (NESSI). NESSI value for base year is 0.377 (2013) and within the select scenarios, it varies from 0.481 to 0.510 in 2031. These variations in extent of sustainability are influenced by underlying technology choices. Thus, Indian electricity system is transitioning towards a more sustainable state. We provide additional insights on how the important questions concerning generation technology pathways for electricity system sustainability transition can be queried and the underlying choices this process involves.

The influence of continued reductions in renewable energy cost on the European electricity system

In the recent years, variable renewable energy (VRE) technologies – most importantly solar photovoltaics and wind power – have undergone a remarkable transformation from niche technologies to increasingly competitive energy suppliers. As the potential for VRE is distributed unevenly across Europe, a Europe-wide cost optimal expansion of VRE will lead to different national and regional expansion rates of VRE. To facilitate such a Europe-wide cost optimal expansion of VRE a fair cost distribution among all European countries is needed. Therefore, we analyse and discuss how expected future decreases in investment costs for selected VRE (photovoltaics, concentrated solar power, wind onshore, and wind offshore) will affect the pan-European and national electricity systems. This is done by comparing three cost scenarios with a reference case, calculated using a European electricity system model. Our results show that the assumed cost reductions lead to an especially pronounced increase of PV distributed unevenly across Europe. In addition, higher shares of VRE show the effect of shifting electricity exchange patterns throughout Europe which also reduce cost benefits for economies of electricity exporting countries. Hence, there might be a lack of agreement in Europe about where and how to expand and integrate VRE if costs of expanding and integrating VRE are not distributed in a fair way between the European countries. In addition, these possible barriers of expanding VRE Europe-wide in a cost-optimal way might hinder the exploitation of cost synergies or even slow down VRE expansion on a European scale.

Hybrid Electrical Generation for Grid Independent Oil and Gas Well Fields

In Perú today, fossil fuels including petroleum, diesel fuel and natural gas are used to produce electrical energy for oil field extraction purposes. Due to their remote geographic locations, oil and gas fields are not linked to the national interconnected electricity system (Sistema Eléctrico Interconectado Nacional or SEIN). Therefore, high investment costs are required to produce electricity in their remote locations.Wind power generation is a mature technology used worldwide. Perú has a substantial potential to produce electricity using wind turbine generators. Evidence of this includes the county's 164 MW of installed capacity, distributed among four operating wind farms that provide power to the electricity market. In 2018, three additional wind parks are expected to be commissioned. They will add another 162 MW of pollution-free energy, in total representing 3.8% of the power supplied to Perú's national power grid. The purpose of this article is to present the research that assessed the implementation of a hybrid wind-thermal natural gas system to provide electrical power for the Block X-Talara oil field and estimate the reductions in fuel consumption and CO2 gas emissions.

An assessment of CO2 emissions avoided by energy-efficiency programs: A general methodology and a case study in Brazil

Abstract Energy efficiency has been proposed as one of the most effective instruments for mitigating greenhouse gas emissions. However, the methodologies to estimate the impact of energy savings on these emissions are generally aggregated and simplified. This study presents an approach for evaluating the emissions avoided by energy-efficiency programs; decomposing the energy savings in the national electrical system load curve and correlating it with the emission factor observed in different periods of this curve. This methodology was applied to the three main programs that promote the rational use of electricity in Brazil: National Electric Energy Conservation Program (PROCEL), Energy Efficiency Law and Energy Efficiency Program (PEE) coordinated by National Agency of Electric Energy (ANEEL). A specific mitigation effect ranging from 0,329 to 0,332 tCO2avoided/MWhsaved is found, which is above the value currently assumed in governmental estimates. The basis for this difference is the fact that energy saved occurs mainly in uses such as lighting, which happen at the load curve peak (or near it) when the thermal power plants are dispatched. The proposed methodology presents more consistent results than those obtained by conventional approaches, endorsing the energy-efficiency role as an instrument for climate change mitigation.

Harmonic analysis of lighting technology application – case study in distribution network: smart city Buzios

This study presents the impact assessment in quality of energy resulting from the implementation of residential artificial lighting and public lighting technologies in the Smart City Búzios, Rio de Janeiro State, Brazil. In the scope are the measurements made in LABLUX – Technical Lighting Laboratory of Federal Fluminense University, with compact fluorescent lamps and light emitting diode (LED) lamps, and two different types of luminaires: Sodium vapour and LED. The simulation of Búzios network was carried out with help of HarmZs, software developed by Center for Electricity Energy Research. Eight application scenarios of lamps and luminaires were made, and checked the voltage distortion generated in the 13.8 kV network, by analysing the criteria established by procedure for distribution of electric energy in the national electric system (PRODIST) (8th Module). Through this analysis it was shown that the LED technology has advantages with regard to reduction of distortions as compared to other technologies for residential lighting or public roads. However, it is necessary a continuous improving of the technology, and new evaluations with the criteria of PRODIST or the long-existing regulation, to ensure the least possible interference harmonics in power system.

Trade-offs between electrification and climate change mitigation: An analysis of the Java-Bali power system in Indonesia

The power sector in many developing countries face challenges of a fast-rising electricity demand in urban areas and an urgency of improved electricity access in rural areas. In the context of climate change, these development needs are challenged by the vital goal of CO2 mitigation. This paper investigates plausible trade-offs between electrification and CO2 mitigation in a developing country context, taking Indonesia as a case study. Aligned with the 2015 Paris Agreement, the Government of Indonesia has announced its voluntary pledge to reduce 29% of its GHGs emissions against the business as usual scenario by 2030. 11% of this should be attained by the energy sector. We incorporate the Indonesian Paris pledge into the modelling of capacity expansion of the Java-Bali power system, which is the largest power system in Indonesia. The LEAP model is used for the analysis in this study. Firstly, we validate the LEAP model using historical data of the national electricity system. Secondly, we develop and analyse four scenarios of the Java-Bali power system expansion from the base year 2015 through to 2030. These include a reference scenario (REF) to reflect a continuation of the present energy mix (REF), then a shift from coal to natural gas (NGS) (natural gas), followed by an expansion of renewable energy (REN) and, finally, the least-cost option (OPT). The shift to natural gas decreases future CO2 emissions by 38.2million ton, helping to achieve the CO2 mitigation target committed to. Likewise, an escalation of renewable energy development in the Java-Bali islands cuts the projected CO2 emissions by 38.9million ton and, thus, assures meeting the target. The least-cost scenario attains the targeted emission reduction, but at 33% and 52% lower additional costs compared to NGS and REN, respectively. The cost-effectiveness of CO2 mitigation scenarios range from 14.9 to 41.8US$/tCO2e.

Maintenance planning of power plant elements based on avoided risk value

In the world’s power sector, a large number of operating coal-fired power units are characterized by a relatively long service life. These power units often constitute the basic source of energy in individual national electric power systems; this implies that their reliability affects the reliability of the entire system of a given country. Therefore, the assessment of the current technical state of the power unit elements and of the risk related to their further operation is an issue of considerable importance. In this paper, we present an analysis of the assessment of the probability of the failure of steam piping being a critical element of the power unit. Theoretical calculations of the probability of failure are presented and a method for its estimation using non-destructive testing of the steel metallographic microstructure is proposed. Further, a rational estimation method of the optimal time to replace the steam pipelines is proposed on the basis of the avoided risk value and the modified net present value index of the discounted cash flows related to the risk.

Integration of renewable energies, flexible loads and storages into the German power grid: Actual situation in German change of power system

Starting from the late 1990’s, the German government decided to change the national electric power supply system dramatically. The main stimulating instrument was the German Law on Renewable Energies (Erneuerbare Energien Gesetz (EEG)), which guaranteed a fixed feed-in tariff to everyone who was willing to invest into renewable generation. Based on the year of commissioning, defined revenues per kWh were fixed for the next 20 years. Due to a very attractive over-funding, more than 1.5 million renewable generation units were connected to the German grid up to the end of 2015. According to the EEG, renewable generation units can feed to the grid wherever they are located and whenever they are able to produce. The old physical principle was and is still neglected, which clearly stated that generation always has to follow the demand—simply due to the limited availability of storages in the power system. Only in cases, when temporarily renewable overproduction exceeds the tolerable loading of lines or transformers respectively endangers the system stability in total, are German grid operators allowed to announce curtailments by emergency measures. Even in such cases, the “not produced energy” from renewable sources has to be funded. Although the installed capacity from renewables is much higher than the peak load in Germany, it contributes only about 32% to German average annual energy. Unfortunately, the regional distribution of renewable generation and load is very different, e.g. in the northeast of Germany, this Renewable Energy (RE)-ratio meanwhile exceeds 100% due to the high RE-penetration and low load. High transits of renewable overproduction from the north to the south will be necessary at nearly every day per year. Therefore, a tremendous change is needed within the German power grid. This paper will give a first overview followed by several others, describing possible solutions on how to overcome this critical situation.

Effects on Greenhouse Gas Emissions of Introducing Electric Vehicles into an Electricity System with Large Storage Capacity

SummaryUnder some circumstances, electric vehicles (EVs) can reduce overall environmental impacts by displacing internal combustion engine vehicles (ICEVs) and by enabling more intermittent renewable energy sources (RES) by charging with surplus power in periods of low demand. However, the net effects on greenhouse gas (GHG) emissions of adding EVs into a national or regional electricity system are complex and, for a system with significant RES, are affected by the presence of storage capacity, such as pumped hydro storage (PHS). This article takes the Portuguese electricity system as a specific example, characterized by relatively high capacities of wind generation and PHS. The interactions between EVs and PHS are explored, using life cycle assessment to compare changes in GHG emissions for different scenarios with a fleet replacement model to describe the introduction of EVs. Where there is sufficient storage capacity to ensure that RES capacity is exploited without curtailment, as in Portugal, any additional demand, such as introduction of EVs, must be met by the next marginal technology. Whether this represents an average increase or decrease in GHG emissions depends on the carbon intensity of the marginal generating technology and on the fuel efficiency of the ICEVs displaced by the EVs, so that detailed analysis is needed for any specific energy system, allowing for future technological improvements. A simple way to represent these trade‐offs is proposed as a basis for supporting strategic policies on introduction of EVs.

FUZZY INFERENCE SYSTEMS FOR MULTI-STEP AHEAD DAILY INFLOW FORECASTING

ABSTRACT This paper presents the evaluation of a daily inflow forecasting model using a tool that facilitates the analysis of mathematical models for hydroelectric plants. The model is based on a Fuzzy Inference System. An offline version of the Expectation Maximization algorithm is employed to adjust the model parameters. The tool integrates different inflow forecasting models into a single physical structure. It makes uniform and streamlines the management of data, prediction studies, and presentation of results. A case study is carried out using data from three Brazilian hydroelectric plants of the Parana basin, Tiete River, in southern Brazil. Their activities are coordinated by Operator of the National Electric System (ONS) and inspected by the National Agency for Electricity (ANEEL). The model is evaluated considering a multi-step ahead forecasting task. The graphs allow a comparison between observed and forecasted inflows. For statistical analysis, it is used the mean absolute percentage error, the root mean square error, the mean absolute error, and the mass curve coefficient. The results show an adequate performance of the model, leading to a promising alternative for daily inflow forecasting.

An approach to prospective consequential life cycle assessment and net energy analysis of distributed electricity generation

Increasing distributed renewable electricity generation is one of a number of technology pathways available to policy makers to meet environmental and other sustainability goals. Determining the efficacy of such a pathway for a national electricity system implies evaluating whole system change in future scenarios. Life cycle assessment (LCA) and net energy analysis (NEA) are two methodologies suitable for prospective and consequential analysis of energy performance and associated impacts. This paper discusses the benefits and limitations of prospective and consequential LCA and NEA analysis of distributed generation. It concludes that a combined LCA and NEA approach is a valuable tool for decision makers if a number of recommendations are addressed. Static and dynamic temporal allocation are both needed for a fair comparison of distributed renewables with thermal power stations to account for their different impact profiles over time. The trade-offs between comprehensiveness and uncertainty in consequential analysis should be acknowledged, with system boundary expansion and system simulation models limited to those clearly justified by the research goal. The results of this approach are explorative, rather than for accounting purposes; this interpretive remit, and the assumptions in scenarios and system models on which results are contingent, must be clear to end users.

Previsões multiescala de vazões para o sistema hidrelétrico brasileiro utilizando ponderação bayesiana de modelos (BMA)

RESUMO O uso de sistemas eficientes de previsão de afluências nas diversas escalas temporais permite otimizar a operação do conjunto de reservatórios hidrelétricos brasileiros, elevando o grau de segurança no fornecimento de energia elétrica e minimizando os custos operacionais. Entretanto, os modelos atuais de previsão utilizados pelo Operador Nacional do Sistema Elétrico (ONS) tendem a ser limitados no horizonte de previsão e na modelagem da dependência existente entre as diversas escalas de tempo, reduzindo a qualidade das previsões. Neste trabalho é proposta uma nova contribuição para os modelos de previsão de afluências em uso pelo ONS a partir do conceito de ponderação bayesiana de modelos (BMA), que permite integrar previsões mensais e semanais de vazões com objetivo de melhorar o desempenho das previsões semanais. As previsões mensais são obtidas por meio de um modelo periódico auto-regressivo exógeno (PARX), que busca captar a persistência das vazões na parte auto-regressiva e a contribuição do escoamento superficial na parcela exógena por meio do uso de informações climáticas de larga escala. Previsões semanais de afluência com até seis semanas de antecedência são obtidas a partir das informações disponibilizadas pelo ONS nos relatórios do Programa Mensal de Operação (PMO). A metodologia proposta é aplicada em séries de afluências semanais aos 28 principais reservatórios hidroelétricos brasileiros. Os resultados de previsão semanal de afluências obtidos com a ponderação das saídas dos modelos de previsão semanal e mensal indicam uma melhoria significativa em indicadores de desempenho de previsões (NS, MAPE e DM) quando comparados com os resultados de previsão oriundos do modelo semanal isolado. Os ganhos obtidos nos indicadores de desempenho são mais significativos a partir da segunda semana de antecedência. A abordagem proposta é flexível em termos de implementação, permitindo integrar outras escalas de previsão assim como diferentes modelos preditivos (por exemplo, modelos de base física).

Smart Grids and their Applicability for the Development of the Electricity Sector for Colombia in the year 2050

Smart Grids are a technology that can be used to implement a sustainable energy scheme of a country. Therefore, this paper proposes the development of a prospective analysis of Smart Grids as a tool to ensure energetic security in Colombia in 2050. Using LEAP software, a base scenario for Colombian energy demand has developed according to current policies, with a time horizon from 2012 to 2050. The energy analysis is based on three scenarios, taking into account the impact of cogeneration in the residential and industrial sector using renewable energy and the power quality indicators. The results show that the implementation of Smart Grids generate energy savings and increasing the coverage of the national electricity system, ensuring energetic security of the country by 2050.

A hybrid SWOT-FANP model for energy policy making in Turkey

ABSTRACTEnergy has a vital role in the development of countries. The situation of global increasing demand for energy, lack of domestic resources, energy prices, etc. forces the policymakers to plan energy policies in detail. In this paper, the strategic energy situation of Turkey is analyzed. This paper presents a hybrid model that combines strength, weakness, opportunity, and threat (SWOT) analysis with the fuzzy analytic network process (FANP) method. In the evaluation process, it is occasionally impossible to take precise information from decision makers (DMs) who can say their assessments relatively and approximately. It is also needed to use fuzzy logic to alleviate this problem. Since the evaluation and selection of alternative energy policies are complex multi-criteria decision making (MCDM) problem, one of the most popular MCDM methods, ANP, is used under fuzziness in this paper. For this aim, four factors and 21 sub-factors are determined and seven alternative policies are evaluated. It is computed that the most important three sub-factors are “major companies’ interest for offshore drilling in Mediterranean and Black Sea,” “developing economy of the country,” and “rapidly increasing energy demand,” respectively. As a result, Turkish energy policy makers are advised to focus on the privatization of electric transmission and distribution facilities, integrating the national electric system with European transmission systems and turning the country into an energy hub and terminal to be able to get the rapid economic growth and mitigate future energy problems.

Scour, Velocities and Pressures Evaluations Produced by Spillway and Outlets of Dam

Paute-Cardenillo (owned by Celec Ep-Hidropaute) is a dam with maximum height 135 m located in the Paute River in Ecuador. Its hydroelectric production will be integrated at the National Electric System of Ecuador with an installed capacity of 600 MW which will produce 3300 GWh per year. To evaluate the stability and safety of the structure, it is necessary to ascertain the shape and dimensions of the scour generated downstream from the dam. We studied the scour, due to the operation of the free surface spillway (700 m3/s) and half-height outlets (1760 m3/s), with three complementary procedures: empirical formulae obtained in models and prototypes, semi-empirical methodology based on pressure fluctuations-erodibility index and computational fluid dynamics simulations. The free surface weir could generate a scour around 21 m, while the intermediate outlet could reach the intact rock, located 34 m below the initial river bed. A pre-excavated basin is proposed and the velocities and pressures are analyzed. The results demonstrated the suitability of combining different methodologies to achieve an adequate resolution of this complex phenomenon.

Financial analysis of photovoltaic configurations for Colombian households

In this paper we analyze the financial feasibility of different solar configurations as alternatives of microgeneration at Colombian homes. We designed five solar solution configurations considering the connection availability to national grid, batteries as a storage option, and the possibility to sell the surplus to the national electricity system. Then we developed a financial model to determine microgeneration cost of each configuration and we compared those costs with the electricity tariff offered by local electricity companies. We found that all the configurations (ie, with or without batteries and grid connection) represent saving money for residential users along several cities, which sets the solar technology as a real solution for electricity micro generation in Colombia.

The shape of future electricity demand: Exploring load curves in 2050s Germany and Britain

National demand for electricity follows a regular and predictable daily pattern. This pattern is set to change due to efficiency improvements, de-industrialisation and electrification of heat and transport. These changes are independent of renewable infeed and are not well understood: contemporary studies assume that electricity load curves will retain their current shape, scaling equally in all hours. Changes to this shape will profoundly affect the electricity industry: increasing the requirements for flexible and peaking capacity, and reducing asset utilisation and profitability.This paper explores the evolution of load curves to 2050 in Germany and Britain: two countries undergoing radically different energy transformations. It reviews recent developments in Europe's electricity demand, and introduces two models for synthesising future hourly load curves: eLOAD (electricity LOad curve ADjustment) and DESSTinEE (Demand for Energy Services, Supply and Transmission in EuropE). Both models are applied to a decarbonisation scenario for 2050, and consistently show peak loads increasing by about 23% points above the change in annual demand, to 103 GW in Germany and 92 GW in Britain. Sensitivities around electrification show that a million extra heat pumps or electric vehicles add up to 1.5 GW to peak demand.The structure and shape of the future load curves are analysed, and impacts on the national electricity systems are drawn.