Long-term reliability evaluation considering wind power integration.

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Faculdade de Engenharia da Universidade do Porto

Long-term Reliability Evaluation Considering

Wind Power

Mariana Costa

Dissertation

Master Degree in Electrical

Supervisor: Prof. Dr. Mauro Augusto da Rosa

Co-Supervisor: Prof. Dr

Faculdade de Engenharia da Universidade do Porto

term Reliability Evaluation Considering

Wind Power Integration

Mariana Costa de Sousa Liquito

Dissertation within the framework

Master Degree in Electrical and Computers Engineering

Major Energy

Supervisor: Prof. Dr. Mauro Augusto da Rosa

Supervisor: Prof. Dr. Jean Akilimali Sumaili

February, 2011.

Faculdade de Engenharia da Universidade do Porto

term Reliability Evaluation Considering

Engineering

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‘Don’t stop ‘till you get enough.’

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Abstract

Renewable Energy. This term is a synonymous of sustainability and technical evolution. The increased use of clean electricity in no longer a utopia, despite not all countries follow the same renewable sources pathway.

The progressive increase of greenhouse effect in the past few decades, the oil shocks and high electricity demand were leading to a situation that has a critical impact all over the planet, thus it was mandatory to take measures to prevent a world crisis. The world’s energy supply is largely based on fossil and nuclear energy sources. These sources of energy, however, will not last forever and have proven to be one of the main causes of our environmental and security problems.

Regarding these aspects, in this document is presented an overview of the adopted measures to integrate alternative energy sources in the conventional generating systems. For this assessment, five different countries were selected since they represent 42% of the world’s installed capacity. These countries were characterized to make possible the assessment of their security of the supply. For this accomplishment, their data information was set up in dedicated software which was adapted for each one of them.

The treatment of wind power variability was performed as well its impact on the system reliability. All the available data about generating system’s evolution was presented and the simulation results were discussed.

Reliability indices such as LOLE, LOLF, LOLD, EENS, EPNS and LOLP were characterized for each studied case and then analyzed and discussed.

Some remarks can be highlighted, such as the insignificant percentage of wind and solar power in the American and Chinese generating systems, the concerning about the fact that Brazil has a large hydro potential to exploit and the legal issues about that subject, and the efforts that small countries representing European Union, namely Portugal and Spain, are taking in order to minimize their dependence of fossil fuels.

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Resumo

Energias Renováveis. Esta expressão é actualmente sinónimo de sustentabilidade e evolução tecnológica. O elevado uso de energias limpas não se apresenta mais como uma utopia mas, no entanto, cada país segue o seu próprio caminho renovável.

O aumento progressivo dos gases de efeito de estuda ao longo das últimas décadas, os choques petrolíferos e o aumento elevado do consumo estavam a levar a uma situação com um impacto crítico em todo o planeta, tornando-se assim imperativo tomar medidas de modo a prevenir uma crise mundial. O fornecimento de energia é praticamente assegurado por combustíveis fósseis e energia nuclear. Prevê-se que estes tipos de energia vejam as suas reservas esgotadas nas próximas décadas e apresentam-se como uma das principais causas de problemas ambientais e de problemas relacionados com a segurança do abastecimento.

Tendo em conta estes aspectos, o que é proposto neste documento é promover uma visão geral das medidas adoptadas para integrar as fontes de energia alternativa nos sistemas de geração convencionais. Para este estudo, foram seleccionados cinco países que perfazem um total de 42% da potência mundial instalada. Para tornar possível a avaliação da segurança do abastecimento, foi necessário caracterizar todos os sistemas e depois aplicá-los e adaptá-los a um programa dedicado.

É descrito o tratamento da variabilidade do vento assim como o seu impacto na fiabilidade do sistema.

Todos os dados disponíveis sobre a evolução dos sistemas geradores e os resultados das simulações são apresentados e discutidos. Os índices de fiabilidade LOLE, LOLF, LOLD, EENS, EPNS e LOLP são caracterizados para cada caso de estudo e também analisados e discutidos.

Algumas notas podem ser ressaltadas, tais como a insignificante percentagem que representa a energia eólica e solar nos sistemas Americano e Chinês, o facto de o Brasil ter um grande potencial hídrico ainda por explorar e as questões legais quanto a essa problemática, e os esforços feitos por pequenos países representantes da União Europeia, nomeadamente Portugal e Espanha, para minimizar a sua dependência de combustíveis fósseis.

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Acknowledgements

The author wants to express her gratitude to her parents for all the opportunities and motivation over the academic pathway.

To Professor Mauro Rosa for all the patience, guidance, good mood and motivation.

To Professor Jean Sumaili for the help with programming.

To Mauro for the company and friendship.

To Diego for his kindness.

To Hrvoje for the several hours spared downloading data.

To Ricardo Ferreira for his availability.

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2.3.10 - RESERVE Outputs ... 35

Chapter 3 ... 37

Wind Power Considerations... 37

3.1 - Wind Data Availability ... 37

3.2 - Characterization of Brazilian Wind Series ... 37

3.3 - Characterization of US Wind Series ... 38

3.4 - Scenarios Evaluation ... 41

3.5 - Wind Data Evaluation – Test System Application ... 45

3.5.1 - IEEEE-RTS 96 H and HW Configurations ... 45

3.6 - Discussions ... 47

3.6.1 - Land Based Results ... 48

3.6.2 - Offshore Sites ... 53

Chapter 4 ... 57

Evaluation of the Security of Supply ... 57

4.1 - Brazil ... 57 4.1.1 - Base Case ... 57 4.1.2 - Planned system ... 58 4.2 - China ... 62 4.2.1 - Base Case ... 62 4.2.2 - Planned system ... 63 4.3 - Portugal ... 65 4.3.1 - Base Case ... 65 4.3.2 - Planned system ... 67 4.4 - Spain ... 69 4.4.1 - Base Case ... 69 4.4.2 - Planned system ... 70 4.5 - US ... 73 4.5.1 - Base Case ... 73 4.5.2 - Planned system ... 74 Chapter 5 ... 79

Conclusions and Future Work ... 79

5.1 - Conclusions ... 79

5.2 - Future Works ... 79

References ... 81

Appendix A - Brazil ... 85

Installed Capacity by Technology ... 85

Appendix B - China ... 99

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Appendix D - Spain ... 120

Appendix E - US ... 130

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List of Figures

Figure 2.1 — World Installed Capacity by Country 2007 (adapted from [3]). ... 4

Figure 2.2 — Past and Present Brazilian Subsystems (adapted from [4]). ... 5

Figure 2.3 — National Interconnect System Installed Capacity 2007 (adapted from [6]). ... 6

Figure 2.4 — Natural Energy Affluent: annual historical average (adapted from [6]). ... 6

Figure 2.5 — Natural Affluent Energy: comparison of long term average between Brazil and North Region (adapted from [6]). ... 7

Figure 2.6 — Monthly Dispatch per simulation year in 10000 years. ... 8

Figure 2.7 — ENA Brazil x Sugar Production in South Centre as percentage of month with better offer. ... 9

Figure 2.8 – China network grid [7]. ... 10

Figure 2.9 – China Installed Capacity 2007 (adapted from [3]). ... 11

Figure 2.10 – Annual energy demand growth by fuel [9]. ... 12

Figure 2.11 – China’s wind turbine installed capacity (MW) 2004~2008. ... 13

Figure 2.12 – Portuguese electric grid [14]... 14

Figure 2.13 – Electrical production by fuel (1980-2004) (adapted from [16]). ... 15

Figure 2.14 – Installed Capacity in Portugal in the end of 2010 ... 15

Figure 2.15 – Total Connected Wind Power in Portugal - Annual Evolution. ... 17

Figure 2.16 – Spanish electric grid [22]. ... 18

Figure 2.17 – Total Spain Peninsular Installed Capacity by 31.12.2009 (adapted from [25]). 19 Figure 2.18 – Electrical Production from 2005 – 2009 by regime (adapted from [25]). ... 20

Figure 2.19 – North American Interconnection [27]. ... 21

Figure 2.20 – U.S. Installed Capacity 2007 [3]. ... 22

Figure 2.21 – Evolution of wind installed capacity in the U.S. 1998-2012 [5]. ... 23

Figure 2.22 – RESERVE model. ... 25

Figure 2.23 – Operating reserve model. ... 26

Figure 2.24 – Two-State model. ... 27

Figure 2.25 – Multi-State model. ... 27

Figure 2.26 – RESERVE model structure. ... 34

Figure 3.1 – Average power for the RPO-100 m wind turbine. ... 39

Figure 3.2 – Average power for some IEC wind turbines. ... 39

Figure 3.3 – 2005 Average power of two different wind turbine altitudes – (80 and 100 m). . 40

Figure 3.4 – 2006 Average power of two different wind turbine altitudes – (80 and 100 m). . 40

Figure 3.5 – Average production (a) onshore and (b) offshore. ... 41

Figure 3.6 – Annual Hourly Average Series. ... 41

Figure 3.7 – Annual Hourly Standard Deviation. ... 42

Figure 3.8 – Annual Hourly Average production on Zero Minute sampling and the Random Minute sampling. ... 43

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Figure 3.9 – Wind Power Variability Characteristic. ... 43

Figure 3.10 – Wind Power Intermittent Characteristic ... 44

Figure 3.11 – Upward and Downward reserve requirement due to wind variation. ... 44

Figure 3.12 – IEEE-RTS 96 H (a) and HW (b) Configurations. ... 45

Figure 3.13 – Average Hydro Power Fluctuations. ... 46

Figure 4.1 – Brazil Generating System 2007 Results. ... 58

Figure 4.2 – Brazil Generating System Evolution from 2015 to 2030. ... 59

Figure 4.3 – Annual Static Reserve. ... 60

Figure 4.4 – Annual Operational Reserve. ... 61

Figure 4.5 – China Generation System 2007 Results. ... 63

Figure 4.6 – China Generating System Evolution from 2015 to 2025. ... 64

Figure 4.7 – China Annual Static Reserve. ... 65

Figure 4.8 – China Annual Operational Reserve... 65

Figure 4.9 – Portugal Generation System 2008 Results. ... 66

Figure 4.10 – Portugal Generating System Evolution from 2015 to 2025. ... 67

Figure 4.11 – Portugal Annual Static Reserve. ... 68

Figure 4.12 – Portugal Annual Operational Reserve. ... 69

Figure 4.13 – Spain Generation System 2008 Results. ... 70

Figure 4.14 – Spanish system evolution from 2015 to 2025. ... 71

Figure 4.15 – Spanish Annual Static Reserve. ... 72

Figure 4.16 – Spanish Annual Operational Reserve... 72

Figure 4.17 – US Generation System 2007 Results. ... 74

Figure 4.18 – US system evolution from 2015 to 2030. ... 75

Figure 4.19 – US Annual Static Reserve (LOLE) for (a) Land Based and (b) Offshore Scenarios. ... 76

Figure 4.20 – US Annual Static Reserve (EENS) for (a) Land Based and (b) Offshore Scenarios. ... 77

Figure 4.21 – US Annual Operational Reserve (LOLE) for (a) Land Based and (b) Offshore Scenarios. ... 77

Figure 4.22 – US Annual Operational Reserve (EENS) for (a) Land Based and (b) Offshore Scenarios. ... 78

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List of Tables

Table 2.1 - Interconnected National System: Thermal Park on 2013 ... 8

Table 2.2 - Historical development of renewable installed power in Portugal (MW) ... 16

Table 2.3 – Spain Energy Production 2008 – 2009 (adapted from [24]) ... 19

Table 2.4 – Unit Commitment Order ... 33

Table 3.1 - Generation of (a) Deterministic and (b) Stochastic Data ... 47

Table 3.2 – System Summary - Reserve Output ... 47

Table 3.3 – Land based Static Reserve Traditional Indices ... 50

Table 3.4 – Land based Operational Reserve – Traditional Indices ... 52

Table 3.5 – Offshore Static Reserve – Traditional Indices ... 54

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List of Acronyms

COPFT Capacity Outage Probability and Frequency Table COPT Capacity Outage Probability Table

EENS Expected Energy Not Supplied ENA Energia Natural Afluente EPNS Expected Power Not Supplied FOR Forced Outage Rate

LOLC Loss of load cost LOLD Loss of load duration LOLE Loss of load expectation LOLF Loss of load frequency LOLP Loss of load probability

MIBEL Mercado Ibérico de Electricidade MTTF Mean Time to Failure

MTTR Mean Time to Repair

NREL National Renewable Energy Laboratory RNT Rede Nacional de Transporte

SEN Sistema Eléctrico Nacional SIN Sistema Interligado Nacional

SONDA Sistema de Organização Nacional de Dados Ambientais TSO Transmission System Operator

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Chapter 1 Introduction

1.1 -

_{Long Term Renewable Energy Outlook}

Energy is essential to world’s economic and social growths. The dependence of electricity has increased exponentially all over the decades and, in present days, it is barely impossible to imagine how life would be without this type of energy. However, the time of cheap electricity has come to an end. The climate changes and the increased dependence on fossil fuels are a reality for all countries.

Aiming at a sustainable, secure and competitive energy development, each country should promote its own energy strategies, thinking globally and acting locally. Over the decades, several protocols were defined and ratified by some countries concerning these issues.

The diversification of the energy mix using alternative and renewable sources is the first step to promote sustainability according to the social and environmental changes. Until the end of 2010, the base of generating systems was coal-fired, liquid-fired and nuclear power plants. For the next 20 years, it is expected that the increased rate of renewable energy in conventional systems achieves a considerable a position.

Brazil has a large exploitable hydro potential, but is experiencing some legal adversities due to the environmental impact of hydro power plants. With these limitations, thermal and bioelectricity seem to be the better solution in order to meet the load demand. But, in a 90% renewable country, it makes sense to start to adopt types of energy that contribute to greenhouse gas effect? Wouldn’t wind and solar energy be better options to let Brazil continue to be a singular country and an example for all the thermal based countries?

China is the most populated country in the world, and its installed generating capacity is beyond the imaginable. The thermal share surpasses in large scale the small attempts of different types of energy. The pollution levels are reaching each day dangerous values due to the abundance usage of low quality coal. Since China is betting on get a remarkable position in world economy and society, especially in Occident, the Chinese government is starting to show the world that environmental issues are also taken into account. Some measures are being taken in order to promote the use of wind and solar electricity and wind parks are being planned all over the windy regions of the country. Without knowing the numbers, this vision

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seems very optimistic and remarkable, but, will the 1% of wind and 0% of solar installed capacities really make the difference?

Portugal and Spain are in a completely reduced scale level than Brazil and China, but the mentality seems to be much more evolved than these countries, when concerning the diversity of energy mix and environmental development. These two countries have their generating parks more or less well-balanced between thermal and alternative types of energy, and seem really anxious in meeting the strategies of European Union concerning the sustainable growth and the extremely strong dependence of fossil fuels. Continuing with this pace, the future seems more green and pleasurable.

United States of America is one of the most technological countries, and associated with all its extravagance are also the high pollution levels. After so many environmental accusations, the country starts to show off the integration of alternative types of energy in order to clean its role as a world menace. Several solar and wind farms are being constructed and exploited, passing from 2% of the installed capacity in 2007 to 6% in 2015 but, for the fifteen years after, US seems to accommodate itself with this value and continuing with its polluter thermal expansion.

1.2 -

_{Objectives of the Dissertation}

The main objective of this Dissertation is to understand how world is responding to the emergent call of renewable alternatives. This work aims to compare the actual state and the evolution of the generating system for five different countries in a 20 year term, especially concerning the integration of renewable energies.

Aiming at achieving a more specific and quantified assessment, some simulations will be performed and the results presented and discussed.

The wind and hydrological variability will be tested and analyzed as well their importance over the security of the supply. Due to particularities of some countries, different wind and hydrological scenarios will be performed using appropriate software and then results will be presented and discussed, in order to evaluate the dependence over renewable sources of energy.

1.3 -

_{Structure of the Dissertation}

Besides this introduction, this document is divided into four chapters. In Chapter 2, a literature review about the integration of renewable energies in Brazilian, Chinese, Portuguese, Spanish and American generating systems is presented. Long-term perspectives for alternative sources policies in the five systems will be compared. This chapter also presents the methodology for the assessment of security of the supply in these systems.

Chapter 3 presents the data treatment and evaluation of the impact of wind power variability over the system’s reliability.

Chapter 4 presents all the available collected data for each system as well the results of the security of the supply evaluation. The five countries stated in Chapter 2 will be characterized and assessed in terms of security of the supply.

Chapter 5 discusses some remarks and conclusions obtained in the previous chapter, where the main results and some overall conclusions are presented. Moreover some future works are suggested.

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Chapter 2 State of the Art

2.1 -

_{Transition from Conventional to Renewable Energy}

Systems

Nowadays, renewable energy is a synonymous of sustainability and technical evolution. The increased use of clean electricity is no longer a utopia, despite not all countries follow the same renewable sources pathway. According with [1] and [2], renewable energy source is defined as any energy resource naturally regenerated over a short time scale that is derived directly from the sun (such as solar thermal and photovoltaic), indirectly from the sun (such as wind, hydropower and photosynthetic energy stored in biomass), or from other natural movements and mechanisms of the environment (such as geothermal and ocean energy).

The progressive increase of greenhouse effect in the past few decades, the oil shocks and high electricity demand were leading to a situation that has a critical impact all over the planet, thus it was mandatory to take measures to prevent a world crisis. The world’s energy supply is largely based on fossil and nuclear energy sources. These sources of energy, however, will not last forever and have proven to be one of the main causes of our environmental and security problems [1]. However, with all these issues about energy security of supply, environmental sustainability and renewable electricity penetration, some research questions can be formulated:

i. Are the current measures towards a sustainable generating system matrix enough for the years to come?

ii. How will the generation system 20 years ahead be?

iii. Is the wind power generation a solution to mitigate greenhouse gas emissions? iv. How will the security of supply 20 years ahead be?

Based on these research questions, a few countries were selected to conduct this study, considering mainly the efforts of each continent have taking towards a sustainable energy systems and how those efforts are reflected in the electricity security of supply, namely on reliability aspects.

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Brazil and China are chosen due to the conditions of emerging countries, representing South America and Asia, respectively. Both countries have an important participation on the worldwide generation matrix. Brazil is 90% renewable, due to the predominant hydroelectricity generation basis, and China has occupied a great share on the worldwide installed capacity.

United States of America is chosen due to its predominant thermal characteristic, and it can be considered one of the most industrialized countries of the world.

Portugal and Spain are being chosen due to their significant efforts on the use of wind power generation and other renewable solutions such as solar thermal and photovoltaic, biomass and so on. It can represent the European Union effort towards a sustainable generation system.

Figure 2.1 shows the participation of each of these countries to the worldwide total installed capacity, where clearly China and the United States represent together almost 40% of the total. Brazil and Spain has together 4 % and Portugal has a small participation. These five countries represent approximately 42% of the total installed capacity of the world [3].

Figure 2.1 — World Installed Capacity by Country 2007 (adapted from [3]).

2.1.1 - Brazil – Renewable Energy Perspectives

Brazil is located in South America, has a land area slightly smaller than the United States and its power system was until few years ago composed of two large interconnected systems. The first one corresponds to the South, Southeast and Midwest Regions, responsible for 79% of the consumption, and the second one, to the Northeast and part of the North Region, responsible for 19% of the consumption. The remaining 2% was associated with an isolated system in the Northern Region. Recently, new large lines were installed, connecting the Northern Region to the others (Figure 2.2) [4].

With about 90% of hydropower production, the Brazilian electrical grid has a privileged composition when compared with the rest of the world. This type of structure guarantees the production and supply of a cleaner energy, and it is possible only because the existence of large reservoirs which regulate the electrical energy offer during all year. However,

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geographical, legal and environmental issues are limiting the construction of hydropower plants with large reservoirs, thus the Brazilian system is in the middle of a transitory process to a new pattern of energy generation.

Figure 2.2 — Past and Present Brazilian Subsystems (adapted from [4]).

Bioelectricity and wind energy have gained special notoriety since complement hydroelectricity in dry period and contribute to the global goal of reducing greenhouse gas emissions. For several years, those types of renewable resources were relegated to second plan due the abundant hydro resources which have smaller and competitive production costs (see [5]).

The irregular rainfall has a strong seasonality, thus the only way to expand the electric system and attend the load demand was the construction of large reservoirs. Those reservoirs allow the stock of large amounts of energy in water form during wet months to be converted in electricity during the dry periods.

Despite Brazil has only 30% of its hydro potential effectively explored, large reservoir system is being conditioned by geographical and legal policy. Regarding environmental issues, new large reservoirs are not allowed to be constructed and even run-of-river hydro plants are experiencing several difficulties in their expansion, thus different types of energy source must be studied in order to expand the system. It is interesting those types of energy to complement the hydro generation during dry periods (see [5]).

2.1.1.1 - Electrical System

In 2007, the installed capacity in Brazil was 95 000 MW [3] and [6], which 85% is represented by hydro power plants and only 15% by other energy sources, especially gas (9%) (Figure 2.3).

Having 90% of natural source energy in such large system, as Brazil, is surely a remarkable and unique achievement worldwide, especially considering that hydropower is renewable, clean and with the lowest generation costs.

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However, this energy has uncertainties linked to the unpredictability of rainfall. In an average year, the hydropower flowing rivers with hydroelectric energy – ENA - surpasses the load demand, but with the energy so uneven distributed throughout the year, high levels of uncertainty need to be taken into account.

*Considering Itaipu’s total installed capacity

Figure 2.3 — National Interconnect System Installed Capacity 2007 (adapted from [6]).

ENA is greater than the load during the wet season between the months of December and April, but the reverse occurs during the dry season, which runs from May to November. Thus, there is a reduction of two thirds of inflows between the months of peak rainfall and peak of drought.

Figure 2.4 shows the long-term historical average for each month of the ENA.

Figure 2.4 — Natural Energy Affluent: annual historical average (adapted from [6]).

85% 1% 9% 2% 2% 1% Other Sources 15%

Hydro* Fuel Natural Gas Coal Nuclear Other

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An important feature of Brazilian electrical system is its design to reduce most of the impact of uncertainty and seasonality of inflows by building large reservoirs. Dams stock water during the wet season in order to be used in dry season, keeping the generation of power stable throughout the year.

Aiming to take advantage of the diversity of inflows and storage capacity of watersheds, the SIN has been expanded, which allows the exchange of electricity between regions through transmission lines at high voltages. These networks reduce, at inter-regional level, the risks associated with the seasonality in availability of energy and the total amount of natural energy tributary [6].

2.1.1.2 - Hydro-Thermal Coordination

As mentioned before, Brazilian electrical system is experiencing a transition in its expansion pattern. The trend line consists on installed capacity expansion without new larger reservoirs, reducing the capability of energy regulation. This trend occurs because the construction of large reservoirs dams is being conditioned due to environmental issues, which forbid hydro plants to have high ratio between flooded land and installed capacity. On the other hand, the remaining hydro potential concentrates in North Region, where rivers flow across large plateaus. With such a plain topography, the construction of reservoirs cannot be justified, because the stored energy would be meaningless. With this scenario, new hydro power plants will have large installed capacity, but small generation during dry periods [6].

Another important change about dam’s incorporation in the North Region will bring to the hydro system, is an increase on contrast between the energy available in wet and dry periods, as can be seen in Figure 2.5.

Figure 2.5 — Natural Affluent Energy: comparison of long term average between Brazil and North Region (adapted from [6]).

Considering the seasonality of energy availability of new hydro plants and the lack of reservoirs capable of stock this energy, Brazilian electrical system will need alternative resources of generation in dry periods [6].

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Facing these problems, the question is which way should be taken to create different types of energy. In practice, the system’s diversification has gone through thermal plants expansion.

Brazilian thermal power plants can be divided in inflexible power plants, which work as regular source of energy and are not subjected to uncertainty of rainfall variations, and flexible power plants which are energy reserves.

In 2007, the SIN had 13 344 MW of installed capacity among all thermal power plants. Until 2013 this type of energy will experience a significant growth, as can be seen in Table 2.1. Thermal installed capacity in 2013 will be of 32 759 MW, mostly composed by flexible thermal power plants, almost two and an half fold the installed capacity in 2007 [6].

Table 2.1 - Interconnected National System: Thermal Park on 2013 Thermal Park Quantity Power Unit

Effective installed power 32,759 MW

Availability 30,012 MWmed*

Inflexible Energy Availability 7,333 MWmed* Flexible Energy Availability 22,679 MWmed*

*1 MW average = 8 760 MWh/year

A thermal plant construction is usually advantageous, since it permits the use of fossil fuels only when is crucial to system security. However, it has its disadvantages. First, hiring several flexible thermal power plants has a problem concerning the uncertainty level of its use and the associated cost to extended dispatch. Flexible thermal represent high capital immobilization based on uncertain use expectation.

Figure 2.6 shows uncertainties and high random level, concerning thermal power plants dispatch. The histogram represents the dispatch frequency between zero (idleness) and twelve months (base dispatch during all the year) [6].

Figure 2.6 — Monthly Dispatch per simulation year in 10000 years.

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In this situation, the average value is not a typical value and the most probable scenarios are base dispatch during all year (probability of 25.0%) or to remain idle (probability of 25.5%). Other disadvantage related with flexible park growth is the volatility increase on system costs. In dry years, even the most expensive thermal units can be dispatch for several months, which have high financial impacts associated.

Hiring a large number of flexible thermal power plants does not seem the intelligent and economic way to create differentiation on Brazilian electrical system, since the costs impact and uncertainty are significant.

However, there is another aspect to take into account: Brazilian electrical system is expanding very quickly and with loss of regulatory capacity it is not recommended allocate the growth demand on flexible thermal if these power plants cannot be committed economically. In practice, there is a need of change in the original thermal use [6].

2.1.1.3 -

Alternative Energies - Bioelectricity and wind energy

Hydro Park can be complemented in different ways: hiring thermal units only to seasonal generation or efficient thermal generation.

A trend to a hydrothermal system is being adopted, where new hydro generation will have higher seasonality with less uncertainty in wet period and less regulatory capability. Bioelectricity and wind energy surge as important, interesting and necessary alternatives.

With seasonal generation, it will possible to expand the system without compromising the regulatory capability. During wet periods, load demand will be supplied by hydro generation, and during dry periods reservoirs will regulate only a part of this demand, the one who has not been supplied by seasonal generation.

Bioelectricity, obtained by sugar biomass, has adequated characteristics to be a seasonal generation. The major potential of this type of electricity is located in South Centre Region, since more than 87% of sugar production is located there.

Figure 2.7 compares the long term average of Total Affluent Energy, monthly, with sugar production in South Centre Region [6].

Figure 2.7 — ENA Brazil x Sugar Production in South Centre as percentage of month with better offer.

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Together with bioelectricity, wind energy is presented as the one with most potential to be integrated in mid-term planning. Wind potential is very interesting and large scale generation may be an attractive and efficient alternative. Two main advantages are taken into account. The first is related with natural resources diversity. Affluences and wind intensity are not correlated, thus if a part of de generated energy would be produced with wind, the energetic impact of bad hydrology will be less aggravated. The second resides on complementarity between wind and hydro regimes. In Northeast, best wind production should be between June and November, which is the driest period in that zone.

Energy supply might be done using also efficient generation thermal units, hired as flexible generation. Hiring flexible thermal with low unitary variable cost is the best way to make the transition to a hydrothermal system with seasonal and low regulation capability. These types of power plants allow a progressive transition, increasing the frequency of thermal units’ dispatch, without having a significant impact on costs.

Due to the transition that Brazilian Electrical System is experiencing, seasonal complementary generation needs to be encouraged, since hydro plants are experiencing some limitations in their exploitation. Bioelectricity and wind energy exploration must be fomented, as well the incorporation of thermal units that can operate in the base of load diagram with interesting production prices [6]. Unfortunately, there are no technical data available to represent Bioelectricity technology.

2.1.2 - China – Renewable Energy Perspectives

China was the country selected to represent the Asian continent, since it is one of largest and populated world countries, and it is experiencing high economic growth. During the period 1970 to 1980, the six regional power networks, Northeast China, North China, East China, Central China, Northwest China and South China, have been formed (Figure 2.8).

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In China, the distribution of energy resources is quite uneven geographically, since 82% of coal deposits are scattered in the North and Southwest and 67% of hydropower is concentrated in the Southwest. Therefore, the North and West are called as the energy basis in China. The main issue is related with the location of energy consumption, since 70% of it is concentrated in central and coastal areas of the country. Thus, transmitting electric power from the energy basis to central and coastal areas is one possibility to mitigate the energy’s deficit in those areas, and it is imperative to develop regional power systems interconnection [8].

2.1.2.1 - Electrical System

In 2001, this country accounted for 10% of global energy demand, but 96% of that value was satisfied with energy produced in China. Today, China’s share of global energy use has increased to over 15%, forcing the country to rely on international markets for most of oil, gas, and coal it consumes. Between 1978 and 2000 the Chinese economy grew at 9% while energy demand grew at 4%. After 2001, economic growth continued apace, but energy demand growth surged to 13% a year. This is the fundamental change in the energy profile of China’s economic growth that has created shortages at home, market volatility abroad, and questions about the sustainability. China is the world’s second-largest energy consumer and the leading source of greenhouse gas emissions [9].

China energy profile is mostly thermal, with coal representing 70% of the total installed capacity, evidenced the lack of energy mix in the country, where only 20% of installed capacity is from hydropower and wind power is residual (see Figure 2.9).

Figure 2.9 – China Installed Capacity 2007 (adapted from [3]).

From 1978 to 2001, China’s economy was able to grow eight-fold without putting significant strain on the country’s energy resources. Institutional reform and price liberalization during this period encouraged more efficient use of coal, oil and natural gas. Demand for these fuels grew at an average annual rate of 4% while the economy grew at 9%.

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As a result, until the mid-1990s China was not only able to produce enough energy to sustain its own development, but had enough for export.

Since then, demand for coal, on which China relies for 67% of its energy needs, has grown 12% annually. Oil demand has grown by 9% and natural gas by 15% over the same period (Figure2.10) [9].

Because of its energy consumption structure and conditions, China will face energy shortage in a long term, specially the supply of oil and gas. Transporting and using resources is difficult because China's large population and its uneven resources distribution [10].

The rapid development of China's economy has largely depended on considerable energy consumption since the 1990’s, with a growth about 5% a year of its total energy consumption, and nearly three times the world's average growth rate. Since the degree of attention to environmental protection is more than any previous period, China's energy industry is facing a severe challenge to balance it with its rapid economic development. China has an overwhelming gap between its energy resources and future need of development in several decades. As this gap increases yearly, the dependence of imported energy will gradually expand, which will become the main issue concerning China's future energy security [11].

Figure 2.10 – Annual energy demand growth by fuel [9].

Therefore, from the view of long economic development, China cannot achieve energy self-sufficiently. It should develop in the direction of efficient, clean and low-carbon power system and insist on the continuous development of new types of energy. Attempts to form diverse energy from the actual should pass by natural gas, nuclear, solar and wind energy [12].

2.1.2.2 - Alternative Energies – Wind Energy

China has is over 1.2 billion inhabitants, and more than 60% live in rural areas where most of households use renewable energy (e.g., biomass, biogas) rather than fossil fuel based energy [12]. -10 -5 0 5 10 15 20 25 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006

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There are various renewable energy sources including hydropower, biomass, solar energy, wind energy, geothermal energy and wave energy currently used in China. It is estimated that the economically potential exploitable renewable energy resources amount to approximately 7.2 billion tons coal equivalent, while the current exploited renewable energy resource is only 0.1 billion tons coal equivalent [12].

However, the move from coal to cleaner alternatives faces several challenges. New hydropower projects encounter political resistance and declining water resources. Nuclear power plants have long construction lead. Under current electricity pricing schedules, natural gas is not a competitive fuel source for power generation in most of the country in the absence of more severe pollution penalties on coal or fuel plants, since it is expensive or increased demand from residential and commercial consumers.

Wind power is becoming cost-competitive in certain areas, particularly with the passage of a renewable energy law in 2005, and China has become one of the world’s largest markets for wind turbines, adding 1 000 MW of capacity in 2006 [9].

China has experienced an unprecedented growth recently with the annual growth of over 100% since 2005. Figure 2.11 illustrates the accumulative installed capacities of China through 2004 to 2008 [13].

In order to complete reverse the energy-consuming and highly-polluting mode of development, the Chinese government is more determined than ever to accelerate wind energy exploitation. Over 100 000 MW wind power is expected to be tagged on the year 2020. In the process of making the country more sustainable and environmentally friendly, numerous problems will inevitably be incurred.

Figure 2.11 – China’s wind turbine installed capacity (MW) 2004~2008.

China’s large-scale wind energy development is very different from the ongoing in Europe and the U.S. in mode. Wind farms in Europe and the U.S. are often scattered over a wide area and most of the wind power and energy is delivered to local loads. However, in China the capacity of the individual wind farm becomes larger and larger and the scale-up development of the wind-abundant areas is notable in a concentrated mode.

The first characteristic is the unbalanced geographic spread and the regional discrepancy between wind energy resource and electricity demands. Most of wind-abundant regions are

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remote from load centers and the local grids are often too weak to accommodate such large amounts of wind power. Coastal regions are in great demand of electricity, but their on-land wind-abundant places are limited and extremely concentrated. However, the northern part of China has relatively small electricity loads, but holds copious wind energy resource.

The second characteristic is that most of the wind energy has to be transferred through Extra High Voltage or even Ultra High Voltage power grids. But some of the bases are over 1000 km or even 3000 km away from the load centers. Apart from the limited amount of wind power and energy that can be absorbed by the local networks, the excess wind power and energy will have to be delivered to the load centers via Extra and Ultra High Voltage grids.

The third characteristic is the complementary characteristic of seasonal change between wind energy and hydro energy resources, just like in Brazil. China has plentiful hydro energy resource which spreads differently for the northern and the southern part of the country. In the southern part, the rainy season passes from March to July. In the northern part, much precipitation occurs in summer, but little in winter. However, strong wind usually blows in spring, autumn and winter. Thus, LSWD will contribute to filling up the hydro energy scarcity in spring and winter [13].

2.1.3 - Portugal – Renewable Energy Perspectives

The first large restructuration on Portuguese electrical system (see Figure 2.12) occurred in 1995 when the coexistence between a public and an independent electrical systems was defined, where the last one was organized following the principles of market orientation.

Figure 2.12 – Portuguese electric grid [14].

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dependence on oil and its derivatives in the total primary energy consumption (49.8%). The first place was occupied by Luxembourg with 58.1% [15]. The Portuguese electrical system had a very large participation of thermal power plants (Figure 2.13) [16].

Figure 2.13 – Electrical production by fuel (1980-2004) (adapted from [16]).

However, in recent years, things are slowing changing. Portugal is promoting renewable energy and it’s starting to play an important role in the Portuguese electrical system.

2.1.3.1 - Electrical System

Portugal has about 18 000 MW of installed capacity, of which more than 25% is hydro power. The thermal power is over 40% of the capacity installed, highlighting the natural gas (21%), which has been growing significantly. Regarding Special Regime Producers, it already accounts for 33% of the total power installed on Portugal, and the wind power already accounts for more than 20% of the total power in the National Electric System (Figure 2.14) [17].

Figure 2.14 – Installed Capacity in Portugal in the end of 2010

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In the first quarter of 2010, Portugal had already 9 229 MW of installed capacity for electricity generation from renewable energy sources. Portugal was, in 2008, the fifth country in the European Union (EU15) with a greater incorporation of renewable energy. Table 2.2 - Historical development of renewable installed power in PortugalTable 2.2 shows the growth that has been observed in Portugal with regard to renewable energy [18].

2.1.3.2 - Alternative Energies – Wind Energy

The knowledge and exploitation of wind resources in the Portuguese territory was slower than in neighboring Spain. Spain in the early 90's became the fourth largest producer of electricity from wind turbines with 15 MW, after Denmark (360 MW), Germany and the Netherlands (15 MW each), which occupied the top spots. Portugal occupied then a position very much minority, the eighth place (with only 2 MW) [15].

This situation was caused by fault of the limited knowledge of wind power, the technology still in development, the little experience with current technology of wind turbines and, hence, a difficult risk assessment by potential producers [19].

Since then, growth in electricity production from wind never stopped. The use of wind energy in Portugal registered a considerable expansion, particularly in recent years. In the period 2001-2007, the installed capacity has grown on average 65% per year, more than doubling between 2003 and 2004. The wind energy production has also increased at equivalent pace, exceeding 3 700 MW in 2007 [15] (see Table 2.2).

Table 2.2 - Historical development of renewable installed power in Portugal (MW)

2002 2003 2004 2005 2006 2007 Annual Average Growth Rate (%) TOTAL HYDRO 4288 4292 4561 4752 4784 4787 1.7 Large Hydro (>30MW) 3783 3783 4043 4234 4234 4234 1.6 Small Hydro (>10 e <=30 MW) 251 251 251 232 263 263 0.7 Small Hydro (<=10 MW) 254 258 267 286 287 290 3.5 Wind 175 253 537 1047 1681 2446 53.8 Biomass (w/ cogeneration) 372 352 357 357 357 357 -0.5 Biomass (wt/ cogeneration) 8 8 12 12 24 24 43.7

Urban Solid Waste 88 88 88 88 88 88 0.0

Biogas 1.0 1.0 7.0 8.2 8.2 12.4 53.4

Photovoltaic 1.5 2.1 2.7 2.9 3.4 14.5 83.2

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Today it is being witnessed an unprecedented dynamism of the situation of wind power in Portugal. As main causes of this situation, may point out:

• The restructuring of the electricity sector started in 1995 and strengthened in 2006, establishing the deepening of liberalization and the promotion of the competition in energy markets;

• The publication of specific legislation in order to promote the development of renewable energy, particularly as regards the updating of the tariff for sale of electricity from renewable sources to the public, introducing a very attractive remuneration, differentiated by technology and system exploration.

The approval of the Renewable Directive, whose implementation in Portugal is to provide for the installation of about 5 000 MW of wind converters in 2012 [19].

In the 1st half of 2010 were connected 109 wind turbines, increasing the wind power connected to the public for 3 571 MW, representing an installed capacity of 3 962 MVA (Figure 2.15). At the end of a semester the wind farms accounted for 21% of the total power connected to the SEN [20].

With increase of the wind power, problems of exploitation have arisen at various levels, namely, network stability and variability of production. While the stability problems forced the installation of wind turbines with new features and technical characteristics suited to a more challenging reality, problems related to production variability arose due to the impossibility of wind turbines guarantee the supply of power and the need to control (reduce) their production, if it's high, off-peak. This situation has forced a reformulation of the Portuguese Regulation of Transmission, with regard to the safety standards for RNT planning, interruptible, frequency deviation, voltage dips and supply of reactive power [21].

Figure 2.15 – Total Connected Wind Power in Portugal - Annual Evolution.

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2.1.4 - Spain - Renewable Energy Perspectives

Since the last in-depth review in 2005, Spain has made substantial progress in its energy policy. It is in full compliance with International Energy Agency oil security requirements and leads in gas diversification and liquefied natural gas development in Europe. Together with Portugal, it has set up the common Iberian electricity market, MIBEL, and has strong ambitions in developing it further. It has also improved the system of end-user tariffs for gas and electricity. Spain is determined and successful in promoting renewable energy and puts increasing emphasis on improving energy efficiency [23]. The Spanish electrical grid is illustrated in Figure 2.16.

2.1.4.1 - Electrical System – Renewable Energy

By the end of 2009, the installed power in peninsular Spanish generator park increased 3 133 MW, resulting as 93 729 MW of total installed capacity. This significant value is strongly related with the installation of new facilities to renewable energy, contemplating to more 2 916 MW, which 2 533 MW are from wind parks and 384 MW are from other renewable, and 1 389 MW of combined cycle power plants [24].

Figure 2.16 – Spanish electric grid [22].

Figure 2.17 shows peninsular installed capacity by the end of 2009. The energetic mix is well distributed, since thermal and renewable energy is well balanced.

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Figure 2.17 – Total Spain Peninsular Installed Capacity by 31.12.2009 (adapted from [25]).

Table 2.3 shows the percentage variation each energy resource had experienced between 2008 and 2009. Coal production has decreased 13.6%, while fuel and gas production remain only 0.4% of total energy production. Hydro production had increased 12.7% together with the share of renewable energies (12.6%), most of it due to solar and wind production. Nuclear production has decreased 10.5%, since 2009 had less groups available due to programmed maintenance. Spain has 8 functional nuclear units placed over 6 locations, which represent 8.1% of total electric installed capacity. Coal power plants had produced 13.6% less than the previous year due the decrease of electrical demand and the restructuration of generating structure, adding the large penetration of renewable energies [24].

Table 2.3 – Spain Energy Production 2008 – 2009 (adapted from [24]) 2008 (%) 2009 (%) 2009/08 (%) Coal 14.2 12.6 -13.6 Fuel 0.4 0.4 15.7 Natural Gas 0.0 0.0 12.9 Nuclear 49.9 45.9 -10.5 Hydro 6.5 7.5 12.7 Other Renewable 29.0 33.6 12.6 TOTAL 100.0 100.0 -2.8

Figure 2.18 shows how special regime generation is contributing to supply the load demand. In 5 years, its participation increased 10.5%, which is a notable value since installed power is also increasing. New wind parks and combined cycle gas power plants certainly contribute to these numbers.

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Figure 2.18 – Electrical Production from 2005 – 2009 by regime (adapted from [25]).

2.1.4.2 - Alternative Energies – Wind Energy

In recent years, wind power has entered the mainstream. Prices have dropped nearly to those of conventional power sources, and governments around the world are increasingly interested in renewable energy that uses local resources and reduces greenhouse-gas emissions. In 2007, according to the Global Wind Energy Council, more than 20 000 megawatts of capacity were installed internationally, with the United States, Spain, and China leading the way [26].

Spain is exemplary also in developing wind power. Its generating capacity is the third-highest in the world and will continue to grow fast. It has succeeded in developing a well-integrated system to balance the inevitable variations in wind power generation. A key tool is the world-class Renewable Energy Control Centre operated by the TSO. To ensure that maximum wind generation can be utilized or stored at any given time, the government, the TSO and industry are developing ways to increase the use of electric vehicles and pumped storage [23].

In Spain, where wind turbines curve over hillsides and along highways in certain areas, 2007 was a record year, with 3 523 megawatts installed—compared with an annual average of 1 200 MW.

The rapid expansion owed a great deal to a series of government decrees, which provided the necessary stability to encourage investment. Spanish utilities are required to purchase any wind power produced, and wind-farm operators can choose to receive a set price or sell their power on the market and receive an added premium. Spain ranks third in the world for overall installed power, only behind Germany and the United States.

The Spanish government also developed strict electricity requirements, or grid codes. Because wind is an intermittent resource, providing power only when it blows, the grid has to be able to cope with fluctuations and dips in electricity. When wind accounted for only a small percentage of the country’s power, such dips made little difference. But as this resource achieved greater prominence, split-second losses of power could have caused

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problems, especially since Spain doesn’t have strong grid connections with neighboring countries.

Because wind provides power only intermittently, grid operators working to maximize efficiency need to know how much energy will be available at any given time. Under Spanish regulations, wind-farm operators sell their power to the grid and must predict how much wind they will be contributing; the operators pay penalties for inaccurate prediction [26].

Energy policy in Spain in the coming decade will be shaped by the European Union targets for 2020 on greenhouse gas mitigation, renewable energy and energy efficiency. The country will have to cut emissions from the sectors outside of the EU Emissions Trading Scheme by 10% below their 2005 levels. It will also have to increase the share of renewable energy sources in gross final energy consumption from 8.7% in 2005 to 20% in 2020 [23].

2.1.5 - United States of America – Renewable Energy Perspectives

The North American electricity system is one of the great engineering achievements of the past 100 years. This electricity infrastructure represents more than 320 000 kilometers of transmission lines, serves over 100 million customers and 283 million people.

While the power system in North America is commonly referred to as “the grid,” there are actually three distinct power grids or “interconnections” (Figure 2.19). The Eastern Interconnection includes the eastern two-thirds of the continental United States and Canada from Saskatchewan east to the Maritime Provinces. The Western Interconnection includes the western third of the continental United States (excluding Alaska), the Canadian provinces of Alberta and British Columbia, and a portion of Baja California Norte, Mexico. The third interconnection comprises most of the state of Texas. The three interconnections are electrically independent from each other except for a few small direct current (DC) ties that link them.

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2.1.5.1 - Electrical System

North American electrical system is typical thermal, strongly dependent from fossil fuels. Figure 2.20 shows only 10% of renewable energy in energetic mix, with 8% of hydropower and 2% of wind power, being solar energy almost insignificant.

Figure 2.20 – U.S. Installed Capacity 2007 [3].

2.1.5.2 - Alternative Energies – Wind Energy

The past decade has seen enormous growth in the US wind power. Back in 2000, slightly more than 2 500 MW had been installed. By the end of 2009, that value had arisen to a world-leading installed capacity of more than 35 000 MW [28].

Investments in wind power accounted for 40% of new installed capacity in the U.S. in 2008. Despite this recent growth, wind generation accounts for only 1.3% of total North American production of electricity. Following this trend, is forecasted the growth of wind energy in the U.S., according to the extension of the federal incentive of US$ 21.00 per MWh by 2012, defined by economic recovery act of 2009 [5].

The US wind market has had two policy stimuli for some years. At the national level there has been a Production Tax Credit (with erratic terms/extensions); while a growing number of states followed the Texan example by introducing a state Renewable Energy Standard, requiring a certain percentage of power in the state to come from renewable sources (with wind generally providing the majority of this) [28].

To sustain the growth over a longer period, increase wind energy manufacturing jobs, and solidify wind’s place in the US energy market, the US wind industry is seeking a national renewable energy standard. This would stimulate utilities to buy wind power and conclude power purchase agreements, which are currently difficult to obtain, due to the drop in overall electricity demand, lower natural gas prices, and the absence of a clear national renewable energy policy [28].

Increasing participation of wind energy in the U.S. in the last ten years has been based primarily on financial support provided by the federal government in the form of tax credits. The subsidy policy has come to expire three times (1999, 2001 and 2003) before being

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renewed in subsequent years (Figure 2.21). This uncertainty of the renewal of credit has slowed the growth of installed capacity. The price of wind power is competitive with no incentive to some sources, but is not competitive with existing plants or with new coal-fired plants and natural gas plants. There is a need for incentives for wind energy being actually competitive [5].

Figure 2.21 – Evolution of wind installed capacity in the U.S. 1998-2012 [5].

Another policy issue that needs to be addressed is the regulatory structure for transmission. New transmission is needed to connect the good wind sites with towns and cities – at present planning, financing and permitting are slow and difficult. Many new wind power projects are on hold in the United States due to transmission limitations [28].

2.2 -

_{Reliability Evaluation of Generation Systems}

A power system serves to supply customers with electrical energy as economically as possible and with an acceptable degree of reliability and quality. Modern society, because of its pattern of social and working habits, has come to expect that the supply should be continuously available on demand. This is not physically possible due to random system failures, although the probability of customers being disconnected can be reduced.

In the past, only deterministic approaches to the reliability assessments were used, like the (N-1) criterion. The essential weakness of deterministic criteria is that they do not respond to nor reflect the probabilistic or stochastic nature of system behavior, of customer demands or of component failures. Since the 1930’s were presented and developed some probabilistic methods, ending the need to artificially constrain the inherent probabilistic or stochastic nature of a power system into a deterministic one [29].

There are, usually, three different approaches used in reliability assessment of power systems: analytical, simulation and hybrid.

The analytical methods combine the probabilities of finding a component on forced outage, in a certain moment. This unavailability FOR depends on the equipment’s failure and repair rates, which, in a real system, are estimated using the MTTF and the MTTR [30].

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In the static reserve studies, the unavailability of the generators is associated with a capacity on outage, which can be modeled using just two states or using intermediate states. Using that combination of the states it is possible to determine the probability of the capacities on outage of the entire system, Capacity Outage Probability Table. However, this probability does not give information about the frequency of the occurrence of the failures nor its durations. A column with the cumulative or incremental frequency is normally added to the COPT in order to form the COPFT [31].

The analytical methods most used in order to obtain the COPT and COPFT are the recursive method, where a model of the capacities in service can be created using a simple recursive algorithm that combines all model’s probabilities and transition rates; the Fast Fourier Transform algorithm, which obtain the COPFT using a convolution based on the Fast Fourier Transform [32]; and Gram-Charlier Expansion who, in opposition to the other two methods where the capacity outage table is obtained through the combination of the generators’ states, establishes a theoretical continuous probability distribution for the capacity outage probabilities [33].

In order to obtain the reliability indices is necessary to combine the COPFT and a demand model. The behavior of the total system load can be expressed by a sequence of discrete load levels defined over the period of analysis [34].

For the quantification of reliable or unreliable situations, is essential evaluating some generating capacity reliability indices. The conventional reliability indices are LOLP, LOLE (h/yr), EPNS (MW/yr), EENS (MWh/yr), LOLF (occ./yr) and LOLD (h).

Simulation methods can also be used to estimate reliability indices, like the Monte Carlo simulation methods. While analytical techniques represent the system by a mathematical model and evaluate the reliability indices from this model using mathematical solutions, Monte Carlo simulation methods estimate the reliability indices by simulating the actual process and random behavior of the system [29]. Others simulation methods that are recently being used in reliability assessment of power systems are genetic algorithm and Evolutionary Particle Swarm Optimization applied to reliability evaluation of power systems [35].

Finally, there are hybrid approaches which use both simulations and analytical characteristics in the same method, since Monte Carlo simulation requires a large amount of computing-time; however, it can include any system effect or system process which may have to be approximated in analytical methods. This type of approach can be considered relatively new with few applications on the literature. Next sections will present a reliability program used in this work, which is based on sequential Monte Carlo simulation.

2.3 -

_{Description of the RESERVE Model}

RESERVE model is prepared to perform reliability assessment of generating systems based on probabilistic methods. The generating capacity reserve evaluation problem can be traditionally split in two conceptually different research areas: static reserve and operating reserve. RESERVE model can perform both evaluations at the same simulation. The basic consideration for both analyses is to concentrate all generating units and load in a single bus. This tool also considers special issues like the integration of intermittent power sources (as wind generation) and interconnection impacts.

Long-term reliability evaluation considering wind power integration.

Faculdade de Engenharia da Universidade do Porto