Volume 2 wind energy 2 18 – wind power integration

Volume 2 wind energy 2 18 – wind power integration Volume 2 wind energy 2 18 – wind power integration Volume 2 wind energy 2 18 – wind power integration Volume 2 wind energy 2 18 – wind power integration Volume 2 wind energy 2 18 – wind power integration Volume 2 wind energy 2 18 – wind power integration

2.18 Wind Power Integration JA Carta, Universidad de Las Palmas de Gran Canaria, Las Palmas de Gran Canaria, Spain © 2012 Elsevier Ltd All rights reserved 2.18.1 Introduction 2.18.2 Overview of Conventional Electrical Power Systems 2.18.2.1 Structure of an Electrical Power System 2.18.2.1.1 Generation 2.18.2.1.2 Electrical networks 2.18.2.1.3 Loads 2.18.2.2 Operational Objectives of an Electrical Power System 2.18.2.3 Operating States of an Electrical Power System 2.18.2.3.1 Active power–frequency control 2.18.2.3.2 Voltage control 2.18.3 The Distinctive Characteristics of Wind Energy 2.18.3.1 The Unpredictability and Variability of Wind 2.18.3.2 The Variability of Electrical Energy from Wind Sources 2.18.3.2.1 Effect of wind turbine aggregation on wind power variability 2.18.3.2.2 Effect of the geographical distribution of wind farms on wind power variability 2.18.4 Wind Power and Power System Interaction 2.18.4.1 Comparison between Conventional and Wind Generation Technologies 2.18.4.2 Potential Disturbances in the Interaction of Wind Turbines with the Electrical Network 2.18.4.2.1 Frequency variations 2.18.4.2.2 Voltage variations 2.18.4.2.3 Voltage flicker 2.18.4.2.4 Phase voltage imbalance 2.18.4.2.5 Voltage dips and swells 2.18.4.2.6 Harmonics 2.18.5 Planning and Operation of Wind Power Electrical Systems 2.18.5.1 Repercussions of Wind Power for Power System Generation 2.18.5.1.1 Repercussions of wind power for generation reserve capacity 2.18.5.1.2 Repercussions of wind power for energy storage needs 2.18.5.1.3 Repercussions of wind power for generation capacity 2.18.5.2 Impact of Wind Power on the Power Transmission and Distribution Networks 2.18.5.2.1 Electrical power transmission from remote onshore wind farms 2.18.5.2.2 Electrical power transmission from offshore wind farms 2.18.5.2.3 Integration of wind power in distribution networks 2.18.6 Integration of Wind Energy into MGs 2.18.6.1 MG Modeling 2.18.6.2 Benefits of Wind Energy Integration into MGs 2.18.6.3 Problems Associated with Wind Energy Penetration in MGs 2.18.7 Questions Related to the Extra Costs of Wind Power Integration 2.18.8 Requirements for Wind Energy Integration into Electrical Networks 2.18.9 Wind Power Forecasting 2.18.9.1 Physical Models 2.18.9.2 Statistical and Data Mining Models 2.18.9.2.1 Statistical models 2.18.9.2.2 Data mining techniques 2.18.9.3 Currently Implemented Forecasting Tools 2.18.10 Future Trends References Further Reading Relevant Websites 570 571 571 571 577 579 581 581 582 585 586 586 588 590 591 591 592 593 593 594 594 594 594 595 596 596 598 599 601 602 602 603 606 607 611 611 612 612 613 614 615 615 616 616 616 617 618 622 622 Comprehensive Renewable Energy, Volume 569 doi:10.1016/B978-0-08-087872-0.00221-3 570 Wind Power Integration 2.18.1 Introduction The main application of the first wind turbines that were built at the end of the nineteenth century to convert the wind’s kinetic energy into electricity was in stand-alone systems [1–3] That is, these wind generators were connected to small stand-alone electrical networks and operated in parallel with electrical generators coupled to diesel engines, or incorporated some type of energy storage system which often consisted of a battery bank The main purpose was to provide electricity in remote areas where the installation of transmission and distribution lines from the power generation stations was prohibitively expensive Today, on the other hand, most wind installations fundamentally comprise installation, transmission, and distribution at a low cost These wind turbine clusters, known as wind parks or wind farms [4], are interconnected to the main network, operating in parallel with it in such a way that they are both feeding power into and consuming power from that network While the first wind farms were installed in the 1980s in the United States and then in Europe [3, 4], it was not until the final years of the twentieth century that the numbers of wind farms connected to electrical networks began to rise spectacularly throughout the world [5–10] Wind farms were initially installed onshore (Figure 1), and indeed this trend continues However, in some northern European countries, a combination of the scarcity of suitable onshore sites with exploitable wind resources and certain favorable characteristics presented by the sea has led to the installation of offshore wind farms, as shown in Figure 2, which first began to be developed from 1991 onward [3, 8, 11] The initiative to install offshore wind farms was taken by Denmark, followed by Sweden, Ireland, the United Kingdom, and The Netherlands By the end of 2010, the 27 member states of the European Union (EU) were benefiting from a total installed wind power capacity of 84 278 MW, of which 2946 MW corresponded to offshore installations [5] According to the World Wind Energy Association (WWEA), the installed wind power capacity worldwide as of the end of 2009 amounted to 196 630 MW [6] Figure Whitelee onshore wind farm, Scotland, UK Courtesy of Iberdrola (http://www.iberdrola.es) Figure Horns Rev offshore wind farm, Denmark Courtesy of Vestas Wind Systems A/S (http://www.vestas.com) Wind Power Integration 571 However, mean wind energy penetration, that is, the percentage of the demand for electricity that is covered over a long time period (normally year) in a particular region by electrical energy derived from wind resources, can vary considerably from one country to another In some countries this penetration was less than 1%, while in Denmark a figure of around 21% was obtained [6] For 2008, the mean penetration throughout the EU was 4.2% [8] However, according to the European Wind Energy Association (EWEA) and its reference scenario for 2030, 300 GW of wind power will be installed by that year It is estimated that this power will produce 935 TWh of electricity, half of which will come from offshore installations, and will cover somewhere between 21% and 28% of the electricity demand of the EU [8], depending on the evolution of future power consumption Parallel to the growing numbers of onshore and offshore wind farms which are connected to the high-voltage (HV) electrical network, there has been an increasing interest in proposals for the installation of ‘embedded’ or ‘distributed’ generation (DG), given the benefits such a system can offer [12–19] This type of generation refers to small generators that are normally connected to a distribution network at medium (MV) or low voltages (LV) rather than to a transmission network at high voltages, which is the normal situation in centralized generation (CG) systems The use of DG systems rules out the possibility of including large wind farms or large hydroelectric plants, but does provide the possibility of using generators powered by renewable energy sources, emergency generators, and combined heat and power (CHP) cogeneration systems Among the various options that have been proposed for DG are the subsystems known as microgrids (MGs) [12, 20] MGs are small-scale, low-voltage networks which aim to supply energy to small communities An MG’s generation system is normally hybrid That is, it usually comprises generators powered by a variety of energy sources [21–26], both renewable and conventional, and energy storage devices [27–30] Such a power system supplies energy to loads that are located in the vicinity through intelligent coordination of the whole system These MGs can be designed in such a way that they can normally operate interconnected to the main network [31] or can operate in stand-alone mode [32] There are a number of advantages to the integration of wind energy into already existing networks or into those under development This chapter will examine these advantages, along with the consequences that the unusual characteristics of this energy source (i.e., its unpredictable nature and the fluctuations in the power generated) can give rise to in the network to which it is connected, as well as the effects such integration has on the network’s operational strategies A presentation is also made of distributed systems together with an explanation of the benefits of the integration of wind energy into normal interconnected MGs and stand-alone MGs 2.18.2 Overview of Conventional Electrical Power Systems Most existing electrical energy systems in the world have very similar structures regardless of the country in question They are basically industrial systems geared toward the generation, transmission, distribution, and supply of electricity [33–38] (Figure 3) Historically, the generation of electricity has been undertaken at large power production stations Often, this type of centralized station is located some distance away from the areas of major consumption, and the energy is supplied to these areas via electrical networks Large wind farms and renewable DG systems are connected to these networks by feeding energy into and extracting energy from them The resulting power flow caused by these installations can affect both the installations themselves and the power systems to which they are connected For a better understanding of the problems associated with wind energy integration, an introduction to a number of questions related to electrical power systems is given below 2.18.2.1 Structure of an Electrical Power System Electrical energy systems can basically be structured into three main blocks: generation, energy transmission/distribution networks, and loads A brief presentation of each of these aspects, as well as of control and protection systems, will be made in the following sections 2.18.2.1.1 Generation Power stations traditionally convert the energy stored in a primary energy source like coal, oil, nuclear fuel, gas, or a volume of water at a certain height into electrical energy The most commonly used technologies are hydro, thermal, and nuclear power plants The generation of hydroelectric power (Figure 4) entails the conversion of the potential energy of a volume of water located at a certain height into kinetic energy in a hydraulic turbine and the conversion of mechanical energy into electrical energy in an electrical generator So, hydroelectric power stations require a flow of water and a difference of level in that flow [23, 28, 38–42] Depending on the method used to control the flow of water, hydroelectric plants can be classified into two basic types: run­ of-river power plants and reservoir power plants Run-of-river power plants take part of the flow of a river and direct it toward the turbines There are a variety of possible configurations, but this type of plant can only allow small controlled flows of water through the turbines Reservoir power plants have the capacity to store water by means of a dam and thus control the flow of water through the turbines and, consequently, the production of electricity Thanks to the storage capacity of reservoir power stations, these power stations can be combined with pumping stations to make pumped storage plants The pumping stations are responsible for returning to the dam, or the upper reservoir, the water that has been discharged from the turbines into a reservoir constructed in the lower part of the station In this way, the surplus energy 572 Wind Power Integration Central power stations Substations EHV V > 145 kV Transmission network Very large customers Medium-sized power stations Substations HV 36 kV < V < 145 kV Subtransmission network Large customers Substations HV/MV kV < V < 36 kV DG Distribution network Medium customers MGs V < kV DG MGs Small customers Figure Schematic diagram of the structure of an electrical power system EHV, extra high voltage Figure Cortes de La Muela hydroelectric power station in Cortes de Pallás, Valencia, Spain Courtesy of Iberdrola (http://www.iberdrola.es) Wind Power Integration 573 produced by thermal and nuclear power stations which face certain difficulties in controlling power output can be stored Likewise, the surplus variable energy generated by wind farms can also be stored Hydroelectric power plants employ various systems and devices for their supervision, control, and protection, depending on the type of technology employed and the envisaged operating parameters Smaller hydroelectric power plants (