90279 A Guide to Operational Impact Analysis of Variable Renewables: Application to the Philippines A Guide to Operational Impact Analysis of Variable Renewables: Application to the Philippines ii A Guide to Operational Impact Analysis of Variable Renewables: Application to the Philippines Copyright © 2013 The International Bank for Reconstruction and Development The World Bank Group 1818 H Street, NW Washington, DC 20433, USA All rights reserved First printing: May 2013 Cover photo credits: Clockwise from top left—Megastocker; Cyberjade; Lianem; Chatchawin Jampapha (123rf.com). This document is a product of the staff of the World Bank Group. The findings, interpretations, and conclusions expressed in this report are entirely those of the authors and should not be attributed in any manner to the World Bank, or its affiliated organizations, or to members of its board of executive directors or the countries they represent.The World Bank does not guarantee the accuracy of the data included in this publication and accepts no responsibility whatsoever for any consequence of their use. The boundaries, colors, denominations, and other information shown on any map in this volume do not imply on the part of the World Bank Group any judgment on the legal status of any territory or the endorse- ment or acceptance of such boundaries. The views expressed in this publication are those of the authors and not necessarily those of the Australian Agency for International Development (AusAID). The financial and technical support by the Energy Sector Management Assistance Program (ESMAP) is gratefully acknowledged. ESMAP—a global knowledge and technical assistance trust fund program admin- istered by the World Bank and assists low- and middle-income countries to increase know-how and institu- tional capacity to achieve environmentally sustainable energy solutions for poverty reduction and economic growth. ESMAP is governed and funded by a Consultative Group (CG) comprised of official bilateral donors and multilateral institutions, representing Australia, Austria, Denmark, France, Finland, Germany, Iceland, Lithuania, the Netherlands, Norway, Sweden, the United Kingdom, and the World Bank Group. Contents Abbreviations................................................................................................................................................v Acknowledgments .......................................................................................................................................vi Summary ....................................................................................................................................................vii 1 Introduction ........................................................................................................................................... 1 2 VRE Integration Studies ........................................................................................................................ 3 2.1 Issues Examined in International Variable Renewable Energy Impact Studies ............................................... 3 2.2 Characteristics of the Philippine Power System .............................................................................................. 5 VRE in the Philippines ....................................................................................................................................... 6 Operation and Reserve Requirements.............................................................................................................. 8 Potential High Impacts ..................................................................................................................................... 9 Potential Medium Impacts ............................................................................................................................. 10 Potential Low Impacts .................................................................................................................................... 12 3 Study Guide .........................................................................................................................................15 3.1 Grid Adequacy for Steady-State Operation .................................................................................................... 15 Reference Study: Minnesota “Dispersed Renewable Generation Transmission Study” .............................. 17 3.2 Grid Adequacy for Transient Voltage Response ............................................................................................. 19 3.3 Inertia and Frequency Response of Island Systems ...................................................................................... 22 3.4 Fault Level Adequacy for HVDC Link Operation (and Protection Relays) ....................................................... 24 3.5 Reserve Adequacy for Expected Forecast Errors ........................................................................................... 26 3.6 Reserve Adequacy for Extreme Ramps ......................................................................................................... 29 3.7 Treatment of Wind Power in Long-Term Reliability Assessment .................................................................... 31 3.8 Electromechanical Impact .............................................................................................................................. 31 4 Conclusions ..........................................................................................................................................33 Appendixes A Definition of Balancing and Reserves ................................................................................................................. 37 B Summary of International Experience ................................................................................................................. 39 C VRE Potential and Wind Contracts in the Philippines.......................................................................................... 46 References ..................................................................................................................................................53 iii iv Contents Figures 1 Issues Assessed in VRE Integration Studies Around the World.......................................................................... viii 2 Issues that Can Set Limits for VRE Penetration for the Philippines..................................................................... viii 2.1 Issues Assessed in VRE Integration Studies around the World............................................................................ 3 2.2 Map of Interconnected Regions of the Philippines, with Energy Mix and Demand Centers................................ 4 2.3 Installed Generation Capacity Mix in 2010 for the Philippines.............................................................................. 5 2.4 Demand-Supply Projections for Luzon, Visayas, and Mindanao, Assuming Only Committed Projects are Built Between 2011–30...................................................................................................................... 6 2.5 Installed Wind and Solar PV Generation Capacity at End of 2010 (MW)............................................................... 7 2.6 Types of Reserves Defined by the Philippine Grid Code...................................................................................... 10 2.7 Flow Chart for High Priority Issues....................................................................................................................... 11 2.8 Flow Chart for Medium Priority Issues................................................................................................................. 11 2.9 Flow Chart for Low Priority Issues....................................................................................................................... 12 2.10 Priority Issues to be Investigated in the Philippines............................................................................................ 13 3.1 Issues that Can Set Limits for VRE Penetration................................................................................................... 15 3.2 Example of Transmission Planning for VRE Integration in Spain......................................................................... 17 3.3 Map of Minnesota Electric Transmission Planning Zones with Final Distributed Renewable Generation.......... 18 3.4 Example of Voltage Profile Improvement Due to Implementation of an Operating Measure in Spain............... 19 3.5 Stable and Unstable System Frequency Response Following the Sudden Loss of Generation......................... 23 3.6 Example of Different Wind Power Penetration Levels (0, 25%, 50%, 75% 100%) on the Three-Phase Faults at Selected Bus Bars in Ireland (Around Each Average Value the Minimum and Maximum Short Circuit Currents Over 63 Load Cases are Indicated by the Error Bar)................................ 26 A1 Time Scale for Different Operation Mechanisms and Reserves......................................................................... 37 B1 Issues investigated in VRE integration studies.................................................................................................... 40 B2 Modeling Tools for Different Studies................................................................................................................... 43 C1 Map of Interconnected Regions of the Philippines, Marked with Location of Demand Centers and Potential for Wind Power Development............................................................................................................... 47 C2 Map of Interconnected Regions of the Philippines, Marked with Location of Demand Centers and Potential for Solar Power Development............................................................................................................... 48 C3 Map of Ocean Power Development..................................................................................................................... 49 Tables 2.1 Generation Capacity and Peak Demand in MW for the Philippines in 2010.......................................................... 5 2.2 Comparisons of Percentage of Wind Power to Total Installed Generation Capacity and Percentage of Wind Power Production to Total Electricity Production for Philippines and Top 10 Countries in 2010................. 7 2.3 Renewable Energy Capacity Addition in the Philippines....................................................................................... 8 2.4 Installed VRE capacity and penetration With and Without Interconnectors for the Philippines in 2010 and 2030.................................................................................................................................................... 8 A1 Reserve Categories.............................................................................................................................................. 38 B1 Objectives of Various International VRE Integration Studies............................................................................... 39 B2 Common Methodologies and Models for Various Studies on Impact of VRE Integration.................................. 44 C1 Wind Contracts in the Philippines........................................................................................................................ 50 Abbreviations DoE Department of Energy NREP National Renewable Energy Program ERCOT Electric Reliability Council of Texas P&Q Real and Reactive Power FRT fault ride-through capability PV photovoltaic HVAC High Voltage Alternating Current RE renewable energy HVDC high voltage, direct current RES-E renewable energy sources for electricity MW Megawatt VRE variable renewable energy NEM National Electricity Market (Australia) WPP wind power plant NGCP National Grid Corporation of the Philippines WTG wind turbine generator NREB National Renewable Energy Board v Acknowledgments This paper is part of a World Bank program to sup- and feedback provided by Philippines energy sector port renewable energy development in the Philippines, stakeholders during a technical workshop held in Manila. funded by a grant provided by the Australian Agency for Participants in the workshop included the Department International Development (AusAID). The team leading of Energy, the Energy Regulatory Commission, the the program comprised Alan Townsend and Beatriz Arizu Philippine Electricity Market Corporation, the National de Jablonski, energy specialists from the World Bank East Grid Corporation of the Philippines, and various renew- Asia and Pacific region, and Marcelino Madrigal from the able energy developers and operators. World Bank Sustainable Energy Department Energy Unit. The team would like to recognize editor Sherrie Brown The team’s efforts also benefited from contributions from and graphic designer Laura Johnson for their contributions Defne Gencer (East Asia and Pacific Region Water and to the production of this publication. Last, the team thanks Energy Unit) and logistics and coordination support from AusAID for providing the resources to make this activ- the World Bank office in Manila. ity and its final product possible. The team would like to This paper was contracted to EnergyNautics Consulting acknowledge Aldo Baietti and Hye-Yon Kim for their con- GMBH of Germany. EnergyNautic’s team was led by tributions and for their role in facilitating cooperation with Thomas Ackermann with support from Rena Kuwahata, AusAID counterparts. the main authors of this publication. The paper relies on None of those who have been so generous with their documentation, background reports, and analyses under- help are answerable for any errors, all of which are the taken by the consultants and feedback and recommenda- responsibility of the team. tion from the World Bank, as well as information, insights, vi Summary This document serves as a guide for those wishing to inves- approaches, data requirements, and scenarios that need tigate the impacts of variable renewable energy1 (VRE) to be analyzed to assess different types of impacts are on the operation of power systems, particularly in the described, and are supported by summaries of relevant Philippines. international experience and key reference studies. The work was commissioned by the World Bank in 2011 to enhance the understanding of power system oper- Issues Relevant to the Philippines ation issues most affected by the integration of VRE, based Based on international experience, it was found that, on international experience. The objective is to build capac- although the issues most relevant to a power system ity in the Philippines for determining the important issues depend on its unique characteristics (such as its size, the for the national grid and to enable the Philippines to design, geographical distribution and expected installed capacities carry out, and interpret the results of appropriate and effec- of the variable renewable resources, the system’s operation tive studies. scheme and market structure, the size of the balancing area, The approaches presented in this guide are based on and interconnection capacity), certain issues receive more state-of-the-art international practices, adapted to suit attention than others, as can be seen in figure 1. In particular, local conditions in the Philippines. The guide was devel- with higher amounts of VRE in a system, the complexity of oped through a survey of international VRE integration balancing supply and demand, maintaining power system studies, charting the relevance to the Philippines of key stability, and planning for long-term reliability is increased. elements such as the physical structure of the power sys- However, these issues can be studied with existing power tem, the energy mix, expected level of VRE penetration, system analysis tools, and VRE growth can be managed market structure, and operation practices and standards. simultaneously with integration studies, even to such high These elements were then consolidated through discus- instantaneous penetration levels as 50–80 percent, as seen sions at a stakeholder workshop in Manila, which included in Spain, Denmark, and Ireland. A critical precondition for the National Renewable Energy Board (NREB) and the the smooth transition into a high renewable energy future National Grid Corporation of the Philippines (NGCP). is effective planning based on robust system design, espe- cially for market design, operational procedures, grid infra- The Step-by-Step Study Guide structure, and regulatory performance requirements. The study guide shows how to estimate the amount of For small, weakly interconnected, island systems like VRE that can be integrated into the power system if no those in the Philippines, certain issues are apt to be more changes are made to its present configuration; however, relevant than others, particularly those issues relating to more important, it shows how to determine the potential system voltage stability and frequency control. However, operational impacts if a certain percentage of renewable because the amount of variable renewables currently energy resources are to be integrated. The main modeling installed in the Philippines is low (less than 1 percent 1.Variable renewable energy includes wind, solar, run of river hydro, and ocean energy. vii viii A Guide to Operational Impact Analysis of Variable Renewables: Application to the Philippines Figure 1. Issues Assessed in VRE Integration Studies Around the World Short- Tertiary reserve Generation term (Load adequacy Secondary system wide scheduling following, reserve (Long-term (Outage balancing) (AGC & reliability) & hydro storage regulation) Primary planning) reserve Market dispatch (Governor) & Small-signal S Inertia stability response al (Electromechanical Grid adequacy oscillation) (N-5 contingency & congestion) regional Transient Island Areas with VRE response Sub synchronous (Rotor angle & interaction High VRE penetration voltage) (DE, DK, ES & PT, NL) Fault Fault & l el level Academic studies Voltage control Power Quality local (Short-circuit (Sh current) (Flicker & Harmonics) High VRE penetration (USA, UK, Scandinavia) years 5 month 5 day 5 hr 5 min 5s 500 ms 50 ms 5 ms Time-constant/Period time Source: Authors. instantaneous penetration) in comparison with other sys- tems around the world, there is still time to plan ahead. • Low: items unlikely to be immediate issues but that Therefore, it is recommended that potential impacts be could be incorporated into long-term planning when studied now, while the penetration level is low, so that higher penetration levels are expected. issues can be identified and addressed ahead of time. By learning from other systems with higher penetration levels Issues that Can Set Limits for VRE Figure 2.  and building a robust and adaptable system for future inte- Penetration for the Philippines gration of variable renewables, it will be possible to accom- modate renewables and make a smoother transition to a • Geographically concentrated VRE development causing network thermal limits to be reached reliable future system. High • Weakly interconnected system susceptible to Based on the characteristics of the Philippine power voltage issues system and information available in the public domain, the • Island systems require a minimum level of system inertia issues listed in figure 2 were identified as being particularly • Inappropriate fault level for inter-island HVDC cables Medium • Insufficient short-term operating reserves for the relevant. They are ranked as: expected wind power forecast errors • Insufficient short-term operating reserves for extreme ramps • High: items that are relevant now and should be assessed promptly; • Capacity contribution of wind power Low • Medium: items that could be an issue for island sys- on long-term reliability • Electromechanical impacts tems and should be considered in the future when higher penetration of VRE is expected: and Source: Authors. Summary ix Detailed step-by-step procedures for evaluating the The grid is unique in that it consists of a number of inter- issues ranked as high and medium are presented in this linked small islands, rather than being on a single island like report; general guidelines are provided for those items Luzon and Mindanao. As with Luzon, the impact of new ranked as low. generation on transmission capacity adequacy and voltage It must be noted that the analysis is based on a litera- limits would need to be analyzed, as would be the impact ture survey; therefore, to gain a thorough understanding of on fault levels, particularly at the terminals of the HVDC the issues and their implications, actual system operators interconnector, to ensure that levels remain adequate for should be consulted. correct operation. Although its plans for wind power development are Key Messages modest, the Mindanao grid is currently a self-contained The future penetration level of VRE in the Philippines will island system with limited reserve capacity, and is in need depend largely on the feed-in tariff and Renewable Portfolio of additional generation capacity. The construction of Standard policies currently being developed by the govern- an interconnector to Visayas is being considered, which ment. However, given the decreasing capital costs of wind would alleviate some of the stress on Mindanao’s system. power and solar photovoltaic (PV) technologies, and the However, the details are yet to have been worked out, and short lead time required to build these generation assets, it is unclear to what extent such an interconnection might rapid expansion is a possibility, and the pace of growth of contribute to the reserve requirement. these technologies may vary among the islands. Despite studies showing adequate reserves in the Luzon The question that then arises is, how can the possible and Visayas grids until about 2020, the operational reality impacts on the electric power system be investigated if in the Philippines suggests there could be much less flex- maximum VRE penetration depends on the power sys- ibility as a result of contract conditions on the provision of tem itself ? International experience shows that the VRE regulating reserves. Therefore, it is urgently recommended penetration level depends not only on the physical system that contractual agreements impeding regulation capability design but also on its operational procedures. Both of these of the power system be revised. factors have large degrees of freedom, and by redesigning An analysis by the Philippine Department of Energy the system or changing the detailed operational strategy, (DoE 2011) estimates that approximately 50 percent of penetration levels can be significantly increased. Hence, the additional generation capacity needed to meet future the grid integration study methods in this report do not reserve requirements in the Philippines must be mid-range determine system limits but will lead to recommendations and peaking generation. Modern wind turbines and solar for upgrading the power system or changing its operations. PV inverters can provide some of the features of these types Much of the wind power development is expected to of generation, indicating that growth in flexible wind and occur in Luzon; therefore, higher VRE penetration levels solar PV power would be highly desirable. will be experienced there before in the other two grids. Thus, it is imperative that the responsible parties in the This indicates that studies focusing on Luzon should be Philippines adopt a forward-looking planning approach conducted more thoroughly, and more immediate solu- and explore the possibilities for integrating variable renew- tions may need to be implemented. For instance, most able energy. The issues to be examined in determining the wind power developments are planned for the north of the best development path for the Philippines include the level island, and energy will have to be transferred via transmis- of VRE that can be managed with existing operational sion lines to the demand center in Manila. Thus, the trans- capabilities, the changes that may be required to accom- mission capacity of the system would need to be analyzed modate higher penetration levels, and the associated costs.2 to ensure that thermal and voltage limits are respected. Visayas is connected to Luzon with a high-voltage, direct current (HVDC) interconnector and is expected to have 2. Note that this report does not provide guidance for determining the the second largest development of wind and solar power. economic impact of technical solutions. 1. Introduction The Philippines is facing energy challenges similar to those system is upgraded or operational procedures are amended in many other countries. The main challenges are the need to take into account higher shares of VRE. to build energy infrastructure to deal with growing power As with other countries, the concern in the Philippines demand; maintaining adequate reserves for droughts and is that high levels of RE could cause additional complexities their impact on hydro resources for power generation; due to its variable nature. These concerns mainly revolve developing strategies to deal with climate change and meet- around balancing operations, power system stability, and ing international expectations to reduce greenhouse gas reliability. However, the findings from many VRE integra- emissions; coping with rising fossil fuel prices; and enhanc- tion studies from the European Union and the United ing energy security by making better use of indigenous States are that renewable resources. These factors have led the Philippine government • VRE impacts can be studied with existing modeling to issue policies that promote the development of local tools; renewable energy (RE) for power generation. In 2008, the • VRE growth can be promoted while integration studies Congress of the Philippines enacted the Renewable Energy are conducted; Act (RA 9513, in this report referred to as the RE Act), • high penetration of VRE can be managed (as proven by which aims to accelerate the exploration and development experiences in Spain, Portugal, Ireland, and Denmark); of RE use in the Philippines, including biomass, solar, wind, • a robust transmission design and grid code procedures tidal, wave, and geothermal, in on-grid and off-grid systems. and VRE technical requirements are vitally important; As established in the RE Act, incentives such as feed-in tar- and iffs and a Renewable Portfolio Standard are under devel- • the most suitable solutions for VRE integration issues opment, and are expected to encourage the growth of all can vary depending on power system characteristics. eligible RE sources, including variable renewable energy (VRE).3 This report thus attempts to provide information to Exactly how much VRE can be integrated into the aid the Philippines in determining how to study the opera- Philippine power system, and whether a maximum limit tional impacts of VRE so that a maximum penetration needs to be imposed to ensure the security and reliability limit, if any, can be found. of supply, are overarching issues. The National Renewable The results are presented as a “how to” guide, which Energy Board (NREB), the National Grid Company of the recommends a series of necessary steps for assessing the Philippines (NGCP), and other stakeholders are inves- impacts of VRE on the Philippine power system and deter- tigating ways to assess the impacts that the system may mining the maximum penetration level of VRE, where experience in dealing with growing amounts of VRE, and possible. whether certain maximum limits need to be set until the 3. The term used in the RE Act is “intermittent RE resources, and to include wind, solar, run-of-river hydro and ocean energy.” 1 2 A Guide to Operational Impact Analysis of Variable Renewables: Application to the Philippines The guide first identifies and describes the types of The step-by-step study guide in section 3 describes the issues often considered relevant for VRE integration, main modeling approaches, data requirements, and scenar- based on a broad review of VRE integration studies across ios to analyze to identify the impacts of different levels of the globe (section 2.1 and appendix B). The relevance of VRE penetration. It also indicates the results that should be these issues to the Philippine power system is then assessed expected and how to interpret them, and provides recom- through a review of publicly available information about mendations on which stakeholders to engage in the study. its characteristics (section 2.2). Based on this assessment, Key references are also provided. suggestions are made about which issues might be most Although best efforts have gone into the analysis, it is relevant for the Philippines (section 2.3). Finally, recom- based on a literature survey. Therefore, to gain a thorough mendations are given for studying the issues identified as understanding of the issues and their implications, actual having potentially high impacts, as well as for interpreting system operators and relevant industry stakeholders should the results (section 3). be consulted. 2. VRE Integration Studies 2.1. Issues Examined in International • when the share of power delivered by wind in the gen- Variable Renewable Energy Impact eration mix is relatively high; and Studies • when wind power is added to systems that are weakly With the use of wind power for electricity generation grow- interconnected. ing around the world, the impact of wind variability on power system operation has been a popular topic of study For this report, studies from leading nations in wind (see figure 2.1). Experience thus far shows that more chal- power integration, such as Denmark, Germany, Spain, and lenges arise under the following conditions: Portugal, were reviewed, as were studies from countries Figure 2.1. Issues Assessed in VRE Integration Studies around the World Short- Tertiary reserve Generation term (Load adequacy Secondary system wide scheduling following, reserve (Long-term (Outage balancing) (AGC & reliability) & hydro storage regulation) Primary planning) reserve Market dispatch (Governor) & Small-signal S Inertia stability response al (Electromechanical Grid adequacy oscillation) (N-1 contingency & congestion) regional Transient Island Areas with VRE response Sub synchronous (Rotor angle & interaction High VRE penetration voltage) (DE, DK, ES & PT, NL) Fault Fault & level l el Academic studies Voltage control Power Quality local (Short-circuit (Sh current) (Flicker & Harmonics) High VRE penetration (USA, UK, Scandinavia) years 5 month 5 day 5 hr 5 min 5s 500 ms 50 ms 5 ms Time-constant/Period time Source: Authors. 3 4 A Guide to Operational Impact Analysis of Variable Renewables: Application to the Philippines Figure 2.2. Map of Interconnected Regions of the Philippines, with Energy Mix and Demand Centers Installed Generation Capacity LUZON in Philippines (2001) Wind 0.2% Other 11.9% Metro Manila Thermal 66.3% Hydro 21.6% VISAYAS Cebu Davao MINDANAO Note: Modified from [1] slide 1 and [2] page 55. showing strong growth and significant research activities, • relatively small and islanded systems, such as those in such as Ireland, the Scandinavian countries, the United New Zealand and Tasmania; Kingdom, and the United States. In addition, power sys- • systems with a generation mix or other important fac- tems with the following characteristics similar to those in tors for managing variability with some similarities to the Philippines were reviewed: the Philippines, such as in New Zealand, the National Energy Market in Australia, the New York Independent • systems that are already short in reserves, such as that System Operator, and ERCOT; and operated by the Electric Reliability Council of Texas • small island systems such as those in the Caribbean and (ERCOT); Hawaii. 2. VRE Integration Studies 5 Figure 2.3. Installed Generation Capacity Mix in 2010 for the Philippines Installed Capacity in Luzon Installed Capacity in Visayas Installed Capacity in Mindanao Biomass Hydro Biomass Coal 0.1% 0.8% 0.6% Solar 12.3% Hydro 0.1% 19.6% Wind Coal Oil based 0.3% 20.5% 28.3% Geothermal Geothermal 50.8% Hydro 17.5% 53.6% Oil based Geothermal Coal 27.3% 5.7% Natural Gas 32.1% 23.9% Source: Graphs produced by authors based on information from Table 1. 2.2. Characteristics of the Philippine The installed generation capacity, dependable capacity,4 Power System and peak demand of the three main grids in 2010 are The power system in the Philippines consists of three grids: shown in table 2.1. Luzon, Visayas, and Mindanao (figure 2.2). Electricity pro- Based on the Department of Energy (DoE) informa- duction in each region varies somewhat, with coal-, oil-, and tion, the currently installed generation capacity appears to natural-gas-fired generation in Luzon; geothermal, coal, be sufficient to meet peak demand, even without transfers and oil in Visayas; and mainly hydro and oil in Mindanao (figure 2.3). A high-voltage, direct current (HVDC) inter- 4. For long term planning purposes, the DoE defines dependable capac- ity as the maximum capacity a power plant can sustain over a specified connector links the Luzon and Visayas grids; Mindanao is period modified for seasonal limitation less the capacity required for a self-contained island system. station service and auxiliaries (NGCP 2011). Table 2.1. Generation Capacity and Peak Demand in MW for the Philippines in 2010 System Luzon Visayas Mindanao Philippines Peak demand 7,656 1,431 1,288 10,231 Generation capacity Installed Dependable Installed Dependable Installed Dependable Installed Dependable Total generation 11,981 10,499 2,407 1,744 1,970 1,658 16,358 13,901 Coal 3,849 3,531 786 501 232 212 4,867 4,244 Oil based 1,984 1,586 615 464 594 438 3,193 2,488 Natural gas 2,861 2,756 0 0 0 0 2,861 2,756 Geo-thermal 899 500 964 751 103 100 1,966 1,351 Hydro 2,346 2,101 13 13 1,040 907 3,399 3,021 Biomass 9 5 29 15 0 0 38 20 Wind 33 20 0 0 0 0 33 20 Solar 0 0 0 0 1 1 1 1 Source: [2] page 55 and [3] page 17. 6 A Guide to Operational Impact Analysis of Variable Renewables: Application to the Philippines between the grids. However, projections (figure 2.4) sug- These figures clearly indicate that additional invest- gest that a tight demand-supply situation could develop ments, on top of the generation capacity currently under during the next decade unless new generation enters construction and committed, are required to meet demand the system to supply the growing demand. In Luzon and by 2020 and beyond. Furthermore, despite indications Visayas, supply may be insufficient to cover the required of adequate reserves in the Luzon and Visayas grids until reserves in about 2020, whereas in Mindanao, supply about 2020, the operational reality in the Philippines appears insufficient to secure reserves even now. requires ensuring flexibility through adequate ancillary ser- vices arrangements. Figure 2.4.  Demand-Supply Projections for The Department of Energy (DoE 2011) projects that Luzon, Visayas, and Mindanao, additional generation capacity of about 1,500 MW will Assuming Only Committed Projects be required in Luzon by 2020, and by 2030, an additional are Built Between 2011–30 10,450 MW. Similarly, Visayas will require an additional Luzon 450 MW by 2020 and 2,000 MW by 2030; and Mindanao 25,000 Existing capacity Required reserve margin will require a further 750 MW by 2020 and 1,950 MW by Committed capacity Peak demand 2030. Moreover, approximately 50 percent of the capacity 20,000 should be mid-range and peaking generation (DoE 2009); 15,000 therefore, growth in wind and solar photovoltaic (PV) 10,000 power would be highly desirable. 5,000 VRE in the Philippines 0 As defined in RE Act, variable renewable energy (VRE) sources include wind power, solar PV power, ocean power, 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 2025 2026 2027 2028 2029 30 20 and run-of-river hydro power schemes. Currently, the only Visayas VRE installed in the Philippines is wind power,5 at just over 5,000 Existing capacity Required reserve margin 33 MW, solar PV at 1 MW,6 and run-of-river hydro. Several 3,500 Committed capacity Peak demand run-of-river schemes have been developed in the past 3,000 decades and have been operationally adequately managed; 2,500 the focus of this report on VRE will be on wind power and 2,000 solar PV. Compared with many other countries, these two 1,500 1,000 sources represents an insignificant amount of VRE (figure 500 2.5). 0 As a proportion of total installed generation, the pene- tration of wind power in the Philippines is still relatively low 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 2025 2026 2027 2028 2029 30 20 (table 2.2). Countries with high penetration of wind power, Mindanao measured by both proportion of total installed capacity and 4,000 Existing capacity Required reserve margin proportion of total electricity production, are mostly based 3,500 Committed capacity Peak demand in Europe, led by Denmark, Portugal, Spain, Ireland, and 3,000 Germany. 2,500 The potential for economically exploitable VRE 2,000 resources has been reported in Elliott and others (2001); 1,500 1,000 Renne, Gray-Hanne, and others (2000); Renne, Heimiller, 500 and others (2000); and DoE (undated); and the locations 0 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 2025 2026 2027 2028 2029 30 20 5. There are also run-of-river hydro schemes but no data specific to this technology were available to the authors. Source: [1] slides 6, 8, and 10. 6. Cepalco’s 1 MWp photovoltaic power plant (http://www.cepalco. com.ph/solar.php). 2. VRE Integration Studies 7 Figure 2.5. Installed Wind and Solar PV Generation Capacity at End of 2010 (MW) Installed wind generation capacity Installed solar PV generation capacity China 44,733 Germany 17,320 USA 40,180 Spain 3,892 Germany 27,214 Japan 3,617.2 Spain 20,676 Italy 3,502.3 India 13,065 US 2,519.6 Italy 5,797 Czech Republic 1,953 France 5,660 France 1,025 UK 5,204 China 893 Canada 4,009 Belgium 803 Portugal 3,898 South Korea 572.9 Denmark 3,752 Australia 503.6 Japan 2,304 Greece 206 Netherlands 2,237 Canada 199.6 Sweden 2,163 India 189 Australia 1,880 Slovakia 145 Ireland 1,428 Portugal 130.84 Turkey 1,329 Austria 102.6 Greece 1,208 Switzerland 100 Poland 1,107 Netherlands 96.893 Austria 1,011 United Kingdom 71.5 Brazil 931 Israel 61 Belgium 911 Mexico 28 Egypt 550 Bulgaria 17.7 Mexico 519 Malaysia 14.6 Taiwan 519 Sweden 10.1 1 100 10,000 1 100 10,000 MW MW Source: GWEC for wind data and BP [4] for solar data. are marked in figure C1 (wind), figure C2 (solar), and figure to the 2011 Transmission Development Plan published by C3 (ocean) in appendix C. Substantial plans for expansion NGCP (2011). The National Renewable Energy Program exist for wind power generation at the moment (appendix (NREP) for 2011–30 produced by the Philippine DoE is C). The government plans are to triple the existing installed extracted from this document and summarized in table 2.3. renewable energy capacity of 5,438 MW by 2030 according Table 2.4 shows the potential VRE power penetration for each grid in the Philippines. This metric more accu- rately portraits the potential challenge for power system Table 2.2. Comparisons of Percentage of operators to maintain balance between demand and gen- Wind Power to Total Installed Generation eration. In a conventional power system, power balance is Capacity and Percentage of Wind Power Production to Total Electricity Production for normally maintained by tracking a variable demand with a Philippines and Top 10 Countries in 2010 predictable and dispatchable generation supply. However, when the energy source itself is fluctuating, managing sup- % wind power/total % wind power/ ply becomes difficult, especially without accurate forecast- installed generation total electricity ing of the VRE. The higher the component of uncertainty, capacity production the higher the complexity and resources required to deal Ranking Country % Country % with the dispatch process. Therefore, for system operators 1 Denmark 28.9 Denmark 21.3 and reliable supply, the penetration rate of VRE relative 2 Portugal 20.7 Portugal 18.0 to demand is most important. The worst case scenario is 3 Spain 18.4 Spain 15.3 when demand is at its minimum and wind farms are gener- 4 Germany 16.9 Ireland 10.5 ating at maximum installed capacity). 5 Ireland 13.4 Germany 6.5 Table 2.4 shows that the expected amount of wind Philippines Rank 42 0.2 Rank 36 0.1 power development in the Philippines could lead at certain Source: WWEA, IEA, ENTSO-E. hours to penetration rates of 15–25 percent, specifically 8 A Guide to Operational Impact Analysis of Variable Renewables: Application to the Philippines Table 2.3. Renewable Energy Capacity Addition in the Philippines Installed Capacity (MW) % VRE/total generation capacity Sector 2010 2015 2020 2025 2030 (2030) Geothermal a 1,966 2,186 3,286 3,381 3,461 11.0 Hydro b 3,399 3,740 6,901 8,793 8,793 28.0 Biomass 38 315 315 315 315 1.0 Base load renewables 5,403 6,241 10,502 12,489 12,569 40.1 Wind 33 1,081 1,936 2,378 2,378 7.6 Solar PV 1 270 275 280 285 0.9 Ocean 0 0 35.5 70.5 70.5 0.2 Variable renewables 34 1,351 2,247 2,729 2,734 8.7 Total renewables 5,437 7,592 12,749 15,218 15,303 48.8 a. Depending on the type of technology, it may not be controllable. If this is the case it needs to be categorized as variable renewables. b. We have not separated run-of-river hydro although it should be categorized as variable renewable. Source: Modified from: [9] page 91 and [1]. Table 2.4. Installed VRE capacity and penetration With and Without Interconnectors for the Philippines in 2010 and 2030 System Luzon Visayas Mindanao Philippines Year 2010 2030 2010 2030 2010 2030 2010 2030 Variable renewables (MW) 33 2,400 0 272 1 62 34 2,734 Interconnector ex-port capacity (MW) 150 150 440 440 0 400 – – Minimum demand (MW) 3,828 9,331 716 1,635 644 1,676 5,116 12,267 Instantaneous VRE penetration without 0.9 25.7 – 16.6 0.2 3.7 0.7 22.3 interconnectora (%) Instantaneous VRE penetration with 0.8 25.3 – 13.1 0.2 3.0 – – interconnector b (%) a. Calculated values: Installed wind capacity / Off-peak demand b. Calculated values: Installed wind capacity / (Off-peak demand + Interconnector export capacity) Source: [9] and [10]. in the Luzon and Visayas grids. These levels are moderate associated with energy exchanges and sharing ancillary ser- compared with other power systems in low demand–high vices across inter-island connections. The following guide- wind conditions, such as in Texas (about 45 percent), lines provide a broad view of the issues significant for island Ireland ( about 70 percent), and the Iberian Peninsula systems at various penetration levels (Bayem 2011). (about 100 percent). However, the operators of small, weakly connected island power systems like that in the Operation and Reserve Requirements Philippines should consider investigating some operational The grid operating criteria in the Philippine Grid Code issues earlier, similar to those studied in Tasmania (15–30 (approved by the Energy Regulatory Commission, 2011) percent), New Zealand (about 20 percent), and the islands states that the grid shall be operated so that it remains in of Hawaii (20–35 percent) because of the challenges the “normal state,” even after the loss of one generation unit, 2. VRE Integration Studies 9 largely on the success of the feed-in tariff and the Renewable 0 to 3% • Network capacity Portfolio Standard (RPS) schemes being introduced by the VRE • RE disconnection after disturbances penetration: Philippine government, it may be worthwhile to examine the conditions that could affect the speed of development. The following characteristics, however, indicate that some • Variability issues are expected to challenge the operation and planning 2 to 25% • Inertia reduction of the power system as VRE penetration increases. • Fault ride through behavior VRE • General consensus on a maximum penetration: level of acceptance being 30% of • The Philippine power system is a weakly intercon- intermittent RE nected series of islands. • Economically sound wind power resources are avail- • Measures to exceed the 30% limit (wind and PV forecast) able in the peripheries of the system. Above • To mitigate the impacts • Studies already show that congestion is expected in 25% VRE (PV monitoring, large storage Luzon because wind power development is concen- penetration: capacity) • To promote RES-storage combination trated in the north of the island, whereas demand is in (‘wind+storage’ and PV+storage’ the center and the south. systems). • Operational limits on the HVDC interconnection between Luzon and Visayas do not permit reserves to be transferred from one island to the other, even though transmission line, or transformer. The normal state is classi- Visayas is planned to become a single reserve zone. fied as when Thus, reserves are currently designed to be met locally on each island grid. • the operating reserve margin is sufficient, • the grid frequency is within the limits of 59.7 and The limit on the amount of VRE that can be integrated into 60.3 Hz, the system is expected to depend on the following issues. • the voltage at all connection points is within the limits of 0.95 and 1.05 of the nominal value, Potential High Impacts • the loading level of all transmission lines and substa- Issues that may have potentially high impacts are relevant tion equipment is below 90 percent of the continuous now and should be assessed immediately (figure 2.7). ratings, and • the grid configuration is such that any potential fault • Grid adequacy for steady-state operation: current can be interrupted and the faulted equipment Injection of active and reactive power (P&Q) by new can be isolated from the grid. power plants changes power flow characteristics, poten- tially hitting static thermal and voltage limits, requiring Operation in the normal state, mainly refers to two permanent solutions such as grid upgrades. This is par- concerns: controlling the frequency and the voltage within ticularly a concern for Luzon because transmission is the stipulated limits. At all times, synchronized genera- already constrained in some areas (NGCP 2009, 21), tion capacity must be sufficient to match the forecasted and will only be exacerbated by wind build-up in north grid demand as well as to cover the operating margin (fre- Luzon. quency regulating reserve and contingency reserve) neces- • Grid adequacy for transient voltage response: sary to ensure the power quality, security, and reliability of Weakly interconnected systems are susceptible to volt- the grid. The types of reserves and their requirements are age issues. The reactive power support capability of depicted in figure 2.6. new VRE power plants may be insufficient to prevent Although the current and expected VRE penetration voltage collapse, requiring the installation of external rates are quite low compared with other power systems in devices or implementation of operating limits. the world, because the actual growth of VRE will depend 10 A Guide to Operational Impact Analysis of Variable Renewables: Application to the Philippines Figure 2.6. Types of Reserves Defined by the Philippine Grid Code Primary Response (Governor): Automatic response to frequency, released increasingly from zero to five seconds, and fully available for 25 seconds Load Following and Frequency Regulating Reserves: To cover intra-hour and inter-hour variations in demand Secondary Response (AGC): and generation Automatic response to frequency, fully available in 25 seconds to take over from primary response, and sustainable for at least 30 minutes Operating margin Load following and frequency regulating reserve (LFFR) (%) = average load forecast variance (4% in Luzon) Spinning Reserves: Generation synchronized to the Spinning reserve (%) = grid and ready to take on load capacity of largest with the ability to attain their generating unit on line / reserve capacity level within system peak demand * 100 Contingency Reserves: 10 minutes and sustain new level To cover the loss of the largest for 30 minutes synchronized generating unit or the power import from a single Backup reserve (%) = grid interconnection, whichever Backup Reserves: system planning reserve is larger Generation with fast start capability – spinning reserve, where and can synchronize with the system planning reserve = grid to provide its declared loss of load probability capacity for a minimum period (LOLP) for one year of 8 hours Source: Graphic created by energynautics based on information in Grid Code [12] and WESM [13]. Potential Medium Impacts • Reserve adequacy for expected forecast errors: Issues potentially having medium impacts are important The method for determining secondary and tertiary for island systems with high VRE penetration (figure 2.8). (non-event) reserve requirements and ancillary ser- vices procurement arrangements (including the market • Inertia and frequency response of island systems: structure for ancillary services) may be inadequate for System inertia may be insufficient to prevent frequency expected VRE power forecast errors. excursions that cannot be controlled by primary • Reserve adequacy for extreme ramps: The method reserve. This is more likely for island systems with high for determining primary and tertiary (event) reserve VRE penetration. requirements and ancillary services arrangements may • Fault level adequacy for HVDC operation: The be inadequate to handle weather-related VRE power short-circuit contribution of VRE power plants may ramps. create fault levels that are inadequate for the proper operation of inter-island HVDC cables.7 7. Currently, one HVDC link connects Luzon and Visayas. It has been in operation since 1998 and uses current sourced converter technology. An additional HVDC link is expected to be installed between Visayas and Mindanao grids in the future. 2. VRE Integration Studies 11 Figure 2.7. Flow Chart for High Priority Issues Issues that should be assessed for new wind and solar High priority issues PV generation assets in the MW range Static Voltage Fault current thermal stability contribution of Possible limiting factors limits limits VRE plant • Grid reinforcements • FACTS • Change • Curtailment of • FRT requirement protection VRE plants in for VRE plants settings combination • Dynamic power • Add external with dynamic factor control reactive Options to increase VRE line rating for VRE plants current source Note: Connection studies for generators other than wind farms must cover the following aspects [45]: thermal assessment; voltage assessment; stability analysis (transient); fault current assessment; operational assessment (if necessary); protection assessment Source: Authors. Figure 2.8. Flow Chart for Medium Priority Issues Issues that are not currently relevant but should be investigated in the Medium priority issues near future because they are relevant for island systems Minimum fault Reserve System level for adequacy for inertia Possible limiting factors operation of regulation and adequacy HVDC ramp events • Virtual inertia • FACTS • Creation of requirements for VRE • Reinforce network new reserve • Leave conventional to increase short- category/market generation in circuit level • Increase Options to increase VRE part-load • Leave conventional interconnector • Synchronous generation in capacity condensers part-load • Distribute VRE better over the island Source: Authors. 12 A Guide to Operational Impact Analysis of Variable Renewables: Application to the Philippines Potential Low Impacts the ability of the system to control electromechanical Issues identified as having low potential impacts are stability. This occurs in response to large or small distur- unlikely to become critical until extremely high penetra- bances or to subsynchronous interactions. tion is imminent, but should be investigated to assist robust long-term planning (figure 2.9). Detailed step-by-step procedures for evaluating the issues ranked as high and medium are presented in this • Treatment of wind power in long-term reliability report; general guidelines are provided for the items ranked assessments: When VRE is added, the dependable as low. generation capacity to meet supply reliability standards Figure 2.10 shows the recommended areas of study should be carefully assessed. for assessing the likely impact of integrating VRE into the • Electromechanical impact: Inverter-connected gen- power system in the Philippines. eration displaces synchronous generation and reduces Figure 2.9. Flow Chart for Low Priority Issues Issues that should be assessed with higher VRE target. These are not expected Low priority issues to impact operation now but should be considered for long-term planning to ensure the construction of a robust system. Long-term Electromechanical Possible limiting factors reliability impacts • Accurate estimation • Change conventional of ELCC power plant performance • Aggregation over wider requirements (e.g., ramp geographic area rates) in Grid Code Options to increase VRE • Improve reliability of • VRE plant performance VRE plant by coupling requirements with storage or DSM • Synchronous condenser Source: Authors. 2. VRE Integration Studies 13 Figure 2.10. Priority Issues to be Investigated in the Philippines Short- t Tertiary reserve Generation term (Load (L adequacy Secondary system wide scheduling llowing, following, reserve (Long-term (Outage ) balancing) (AGC & reliability) & hydro storage re regulation) Primary planning) reserve atch Market dispatch (Governor) & S Small-signal Small-sig Inertia Iner lity stability e responsnse response al (Electromechanical acy Grid adequacy oscillation) on) (N-5 contingency & congestion) regional ansie n Transient se response Sub synchronous Rotor ang (Rotor angle & interaction voltage) & Fa Fault F ault level l el ve Voltage control Power Quality local (Short-circuit (Sh -c current) curre (Flicker & Harmonics) years 1 month 1 day 1 1 min 1s 100 ms 10 ms 1 ms Time-constant/Period time Source: Authors 3. Study Guide This section gives step-by-step instructions for investigat- 3.1. Grid Adequacy for Steady-State ing the various impacts to determine whether limits to Operation variable renewable energy (VRE) integration need to be The grid adequacy study investigates whether the addition set. The approaches introduced are based on international of new generation assets causes power flow characteristics experience. and active and reactive power (P&Q) loading on network The issues that may become limiting factors for the elements to change outside static thermal and voltage lim- Philippines are shown in figure 3.1. They are ranked as its. This is a standard study that should be conducted for High: items that are relevant now and should be assessed any type of generation, not just renewables, and can be used promptly; Medium: items that could be an issue for island to determine the maximum amount of VRE that could be systems and should be considered in the future when integrated without breaching these limits. The report by higher penetration of VRE is expected: and Low: items Minnesota Transmission Owners (2008)8 is a good exam- unlikely to be immediate issues but that could be incor- ple of such a study. porated into long-term planning when higher penetration Most studies assess areas of the network that require levels are expected. Detailed step-by-step procedures for reinforcement or augmentation to accommodate a cer- evaluating the issues ranked as high and medium are pre- tain amount of VRE (figure 3.2), rather than attempting sented in this report; general guidelines are provided for to determine limits to the amount of integration. Because those items ranked as low. wind power plants (WPPs) are often located far from load centers and at the margins of the grid, and because less Figure 3.1.  Issues that Can Set Limits time is required to build wind and solar photovoltaic (PV) for VRE Penetration power capacity than to build transmission capacity, it is vital that this study be performed well ahead of time as part of • Geographically concentrated VRE development long-term grid planning. This advance work will enable a causing network thermal limits to be reached High • Weakly interconnected system susceptible to robust power system to be designed and built, one that can voltage issues adapt to a variety of potential renewable energy develop- • Island systems require a minimum level of system ment scenarios. inertia • Inappropriate fault level for inter-island HVDC cables Medium • Insufficient short-term operating reserves for the expected wind power forecast errors • Insufficient short-term operating reserves for extreme ramps • Capacity contribution of wind power Low on long-term reliability • Electromechanical impacts Source: Authors. 8. For more information, see pp. 39–41 of that study. 15 16 A Guide to Operational Impact Analysis of Variable Renewables: Application to the Philippines Objectives A) Maximum VRE penetration study To determine the maximum amount of VRE that can be integrated without violating static thermal and voltage limits. B) Identification of key infrastructure To identify key transmission infrastructure development that would be required to integrate high levels of renewable energy sources for electricity (RES-E) advocated by government policies. Methodology Based on a number of future generation scenarios depicting the diverse development possibilities for VRE in the Philippines, perform steady-state load flow analysis. A) Maximum VRE penetration study Apply future demand and generation availability scenarios (see Scenarios for details on setup of scenarios), starting with the maximum VRE output for each scenario. Study the power flows for (N) and (N–1) conditions to see if they result in any static limit violations. If a violation occurs, decrement the VRE generation output and study the power flow again. Repeat this process until no violations occur. B) Identification of key infrastructure Apply future demand and generation availability scenarios with the expected level of VRE dispatch under (N) and (N–1) conditions to identify areas that are likely to experience congestion; areas that are likely to experience over- or under-voltage issues; and areas of the network that will need to be extended. Based on the findings, infrastructure that will be required to accommodate the VRE in each scenario can be evaluated. These infrastructure changes may be in the form of (but not restricted to) transmission line upgrades, and flexible alternating current transmission system (FACTS) devices. Infrastructure common to all scenarios can then be identified as key solutions for integration of VRE. Additionally, the associated costs of each scenario can be calculated for comparison. Scenarios A number of generation scenarios should be studied to adequately capture the range of possible future developments in the following: installation area and capacity of wind and solar power, including existing plans and approved RE projects (for example, in a queue system) and based on political and economic assumptions (for example, fuel prices, carbon price, feed-in tariffs, technology price, government support schemes, and so forth); phasing out of conventional power plants; and delays to existing generation and transmission expansion plans. The ability of the transmission system to deliver power supply under “stressful” conditions should be assessed to identify where reinforcements may be required. Such situations typically occur during peak demand periods with high and low wind or solar power availability; off-peak demand periods with high and low wind or solar power availability; system contingencies (N–1); and periods with extreme weather, such as storms, based on an analysis of historical weather events. However, other situations might also be critical, depending on the power system. Model Philippine transmission grid: AC power flow model with the existing topology and typical operation scheme requirements (open breakers and so forth). Wind power generation: Aggregated P&Q output of WPP based on fixed wind speed for high and low wind power outputs. Solar PV power generation: Aggregated P&Q output of solar PV power plant based on fixed irradiance for high and low power outputs. Other generation: P&Q model with full availability corresponding to the time point analyzed, including external reactive power devices. Data Demand: Projected future peak and off-peak demand for all nodes in network model (maximum and minimum demand requirements in MW). Generation: Projected future installed generation capacity and corresponding availability during peak and off-peak periods. How to If the simulation results in static thermal or voltage limit violations, a maximum VRE penetration limit may need to be imposed interpret unless further measures are taken (such as increasing transmission capacity). Even if more VRE capacity is built, it will not be results and possible to transport it to demand centers. The energy will simply be curtailed. the expected The most common solution for alleviating congestion is to upgrade the transmission lines to increase the active power-carrying output capacity. However, in many cases it takes longer to build transmission lines, than it takes to build new WPPs and solar PV plants. Temporary solutions may be implemented, such as introducing dynamic line ratings or using phase-shifting transformers. Ultimately however, it is important to have a good understanding of the areas that are likely to be affected in the future and ensure a robust transmission planning process is in place that anticipates critical infrastructure for integration of the expected future VRE development. It is expected that congestion will exist in Luzon in any attempt to transport wind energy concentrated in the north of the island to the demand center in Manila. This has in fact already been observed (NGCP 2009, 21). 3. Study Guide 17 Figure 3.2. Example of Transmission Planning for VRE Integration in Spain Source: [14] slide 22. http://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CDYQFjAA&url=http%3A%2F%2Fwww.feed-in-cooperation. org%2FwDefault_7%2Fdownload-files%2F2nd-workshop%2Fsession2alonso.pdf%3FWSESSIONID%3Dccdf1f3ce9cff60fc2ea590f0a7e5213&ei=zqtJUZqLFYPdPYHqg fAP&usg=AFQjCNFmVTH4-hOtylegICOQmaQtxyQ-uQ&bvm=bv.44011176,d.ZWU Reference Study: Minnesota “Dispersed of wind power. For the purpose of the study, the criteria for Renewable Generation Transmission Study” an overloaded transmission facility was 100 percent of its This study was conducted to assess the possibility of continuous rating limit for both system intact and N–1 accommodating 600 MW of dispersed renewable genera- contingency conditions. In addition to the base case (no tion in the state of Minnesota. The state was divided into wind power), 42 single sites were examined. The genera- 42 sites across the five planning zones. The maximum tion output at each site was initially set to 40 MW before amount of wind power that could be connected at each site system intact and contingency analysis was performed. with minimal impact to the transmission system was deter- The results were compared with the base case, and when an mined (see figure 3.3). overload resulted, the case was rerun at 35 MW and decre- Step 1: Alternating current (A/C) steady-state analysis mented in 5 MW steps until an output level was reached at was conducted at each site for summer peak and summer which no overloads occurred. off-peak models. The analysis was performed under the Step 2: Sites within a zone were aggregated and studied assumption that generation capacity would be added to again for overloads. In each zone, the aggregated capacity only one site in the state and all other sites would be held was 225 MW. In a process similar to Step 1, the total wind to 0 MW. A comparison of two cases, with and without the power in a zone was decremented by 25 MW until no over- wind power installations, allows identification of transmis- loads resulted. sion facilities that are significantly affected by the addition 18 A Guide to Operational Impact Analysis of Variable Renewables: Application to the Philippines Step 3: Finally, a statewide analysis was conducted. All Step 4: The 20 selected locations were tested for tran- statewide facility outages were considered, as were those sient stability after critical regional faults. The impacts on of facilities immediately adjoining Minnesota. From the the overall system and interconnectors were observed to steady-state analysis, 20 locations were chosen for wind see if faults affected regional system stability. power installation, and areas where grid augmentations might be required were identified. Map of Minnesota Electric Transmission Planning Zones with Final Distributed Figure 3.3.  Renewable Generation Source: [20] page 49. http://www.uwig.org/DRG_Transmission_Study_Vol_I_061608045236_DRGTransmissionStudyVolI.pdf 3. Study Guide 19 3.2. Grid Adequacy for Transient voltage support capabilities, installing external reactive Voltage Response power support devices, and setting operating limits. This second grid adequacy study investigates whether the The amount of VRE that can be integrated is highly system can prevent voltage collapse upon the addition of dependent on the fault ride-through capability (FRT) new generation. This is a standard study that should be con- and reactive power support capability offered by the VRE ducted for any type of generation, not just renewables, and power plants. Thus, it is important that the grid code can be used to determine the maximum amount of VRE require the new and existing VRE generation comply with that could be integrated without violating voltage limits. requirements for supplying voltage support capabilities, The Minnesota Transmission Owners report (2008)9 is a and be accurately represented in the study. good example of such a study. Because of the resources it takes to perform voltage Most studies assess the implementation of solutions to stability simulations, it is recommended that this study be accommodate a certain amount of VRE, such as improv- performed after the reference study (3.1) to see if these ing the grid code, using VRE power plants with improved voltage studies result in even more stringent requirements (see figure 3.4). 9. For more information, see Minnesota Transmission Owners (2008, 38–40). Figure 3.4. Example of Voltage Profile Improvement Due to Implementation of an Operating Measure in Spain Source: [14], slide 50. http://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CDYQFjAA&url=http%3A%2F%2Fwww.feed-in-cooperation. org%2FwDefault_7%2Fdownload-files%2F2nd-workshop%2Fsession2alonso.pdf%3FWSESSIONID%3Dccdf1f3ce9cff60fc2ea590f0a7e5213&ei=zqtJUZqLFYPdPYHqg fAP&usg=AFQjCNFmVTH4-hOtylegICOQmaQtxyQ-uQ&bvm=bv.44011176,d.ZWU 20 A Guide to Operational Impact Analysis of Variable Renewables: Application to the Philippines Objectives A) Maximum VRE penetration study To determine the maximum amount of VRE that can be integrated into the power system without violating voltage limits. B) Assessment of reactive power capability requirements To assess the level of reactive power capability required to integrate high levels of RES-E advocated by government policies. Methodology Voltage issues are generally local issues, therefore studies should concentrate on regions in which voltage problems are already known to exist. These regions are often where power transfer limits or load limits (or both) have been imposed on system operation. Based on the expected future system configuration, investigate the behavior of the system during and after low voltage conditions. Perform the investigation by applying future demand and generation availability scenarios and performing dynamic simulations of voltage dips caused by events such as short-circuit faults at the connection point of large WPPs and solar PV plants. Monitor the voltage at the connection point in time domain, covering the periods during and after the fault for about 20 seconds. A) Maximum VRE penetration study Starting with the most severe scenario, which is usually maximum VRE output and either maximum transfer or load depending on the voltage issue, check whether the voltage recovery characteristic complies with grid code requirements. If it does not, decrement the VRE generation output and study the voltage again. Repeat this process until no violations occur. B) Assessment of reactive power capability requirements Apply the most severe scenario as was done for the maximum VRE penetration study, and observe the voltage recovery. If there is a violation, place a fictitious reactive power compensation device at the desired point, and study the voltage recovery again. Based on this analysis, develop voltage support measures and assess their effectiveness. These may include stricter low voltage ride through or voltage support requirements for VRE power plants, installation of external voltage support devices, and implementation of operation restrictions. Additionally, the associated costs of each scenario can be calculated for comparison. Scenarios It is recommended that a number of scenarios be studied that consider issues such as the levels of voltage support capability offered by different types of VRE power plants and critical load and power transfer levels for voltage stability in the region. The evaluation should consider a high VRE production case in which minimum conventional synchronous generation is online. (Voltage stability problems normally occur in heavily stressed systems.) Model Philippine transmission grid: Dynamic alternating current (AC) model with the existing topology and typical operating requirements scheme (open breakers and the like), including validated dynamic models for all conventional generators for the area concerned. Depending on the detail desired, the subtransmission system may need to be modeled as well, particularly in relation to transformer tap controls, any reactive power compensation in the system, and voltage-dependent loads. However, to investigate the general impact, it may be adequate to assume that transformer taps are fixed and that WPPs operate at unity power factor, that is, that they do not participate in voltage control. (This was done in the All Island TSO Facilitation of Renewables Study , for example. See Bömer and others 2010.) Wind and solar PV power generation: Aggregated dynamic model of power plant including its low voltage ride-through and voltage support capabilities. Include P&Q output based on fixed wind speed (or solar irradiation) for high power outputs. Loads: Static load or voltage-dependent loads such as inductive loads. Other generation: Dynamic models including excitation systems, power system stabilizers, and external reactive power devices. Protection relays: Generator and system protection relays that cause generators to cut off when low voltage is detected should be modeled. Data Demand: Projected future peak and off-peak demand for all nodes in network model (maximum and minimum demand requirements in MW). Generation: Projected future installed generation capacity and corresponding availability during peak and off-peak periods (in MW). An estimate of the voltage support capability of future WPPs and solar PV plants. These capabilities should be benchmarked against an existing WPP with “typical values” rather than assuming the worst case behavior, given that performance standards vary between WPP sites. (continued) 3. Study Guide 21 How to If the simulation results in a voltage collapse or voltage limit violation, maximum VRE penetration limits may need to be interpret imposed unless further measures are taken (such as adding dynamic volt-amps reactive [DVar] systems). results and The most common solution for preventing voltage collapse is to require low voltage ride-through capabilities from the VRE the expected power plants in the grid code. Low voltage ride-through capabilities can be supplied by modern wind turbines and solar PV output inverters, but can also be supplied by external reactive power devices like DVars. For voltage regulation, dynamic reactive power support capabilities can also be demanded from the VRE plants or provided by external reactive power devices like static reactive compensators (SVCs). Because performance requirements are likely to vary among locations, the requirement may be determined on a location-by- location basis, as is done in the Australia National Electricity Market (in which each plant must meet its own unique technical standard). Alternatively, a standardized approach could be used as in Europe, where the minimum performance requirement from a power plant is stipulated in the grid code. Voltage issues are expected to be prevalent in areas that are weakly interconnected. Because no FRT requirement is applied at present, a hard limit on VRE that can be installed in certain regions or connection points is likely to exist. However, rather than limiting the amount of VRE that can be integrated based on the current grid code (with no FRT requirement), it would be better to set a reactive power support capability requirement in the grid code to eliminate these types of problems. For grid planning studies to generate robust solutions and solar power, consultation with industry is strongly rec- that are widely supported by both industry and govern- ommended to ensure wide acceptance of the study find- ment, relevant stakeholders must be involved in the project ings. Also, support from the government and regulatory preparation phase. Stakeholder input will be valuable dur- authority will aid with gaining credibility and maybe even ing discussion of the variety of assumptions that can affect policy-backed support to drive the development of key the diversity of future scenarios. Particularly with regard to transmission augmentations. the anticipated geographic areas of development for wind Stakeholders National Grid Corporation of the Philippines (NGCP), National Renewable Energy Board (NREB), renewable energy required advocates, generation project developers, Department of Energy (DOE), Energy Regulatory Commission (ERC) Key reference Power flow and stability studies: studies All Island Grid Study WS3, Department of Communications, Marine and Natural Resources in the Republic of Ireland and the Department of Enterprise, Trade and Investment in Northern Ireland (TNEI), 2007–12. EWI, E.ON Grid, EWI, RWE Transport Grid Electricity, VE Transmission. 2005. “Energy Management Planning for Integration of Wind Energy into the Grid in Germany, Onshore and Offshore by 2020,” Deutsche Energie-Agentur GmbH (dena), Cologne. Southwest Power Pool Wind Integration Study, WITF Final Report, SPP (Charles River Associates), 2010–01. Integration of Renewable Resources: Transmission and Operating Issues and Recommendations for Integrating Renewable Resources on the California ISO-controlled Grid, California ISO, 2007–11. Growing Wind: Final Report of the NYISO 2010 Wind Generation Study, NYISO, 2010–09. CREZ Reactive Power Compensation Study, ERCOT (ABB), 2010–12. Market-coupled studies: TradeWind, EC (EWEA, Risoe, et al.), 2009–05. ENTSO-E and European Commission. 2010. “European Wind Integration Study (EWIS): Towards A Successful Integration of Large Scale Wind Power into European Electricity Grids,” Brussels. Large grid augmentations and EHV overlay studies: EnerNex Corporation. 2011. “Eastern Wind Integration and Transmission Study,” National Renewable Energy Laboratory, Golden Colorado. SSP EHV Overlay Project, SPP (InfraSource, PowerWorld), 2007-06. Strategic Midwest Area Renewable Transmission (SMARTransmission) Study, Quanta Technology, 2010. General: Transmission Planning for Wind Energy: Status and Prospects, C. Smith, et al., 2010–10. The Cost of Transmission for Wind Energy: A Review of Transmission Planning Studies, A. Mills, et al., Berkley National Laboratory, 2009–02. 22 A Guide to Operational Impact Analysis of Variable Renewables: Application to the Philippines 3.3. Inertia and Frequency Response as demonstrated by the Irish “All Island TSO Facilitation of Island Systems of Renewables” study (Bömer and others 2010). Because The inertia and frequency response study investigates the Philippine power system is a series of island systems whether the power system has adequate inertia to prevent interconnected by weak links, a hard technical limit to frequency excursions that cannot be controlled by primary VRE penetration may be required. This study may reveal reserve. the maximum limit of “inertia-less” generation that can be As identified by the IEA Wind Task 25 report, fre- integrated in relation to total power production. The Irish quency control and inertial response are not considered “All Island TSO Facilitation of Renewables” study commis- crucial problems for wind power integration at the present sioned by Eirgrid, resulted in a 60–80 percent “inertia-less” levels of penetration seen around the world. However, it penetration limit. can be a challenge for small (particularly island) systems, Objective To determine whether a limit exists for the penetration of “inertia-less” generation in each of the regional grid systems (Luzon, Visayas, and Mindanao). Methodology The system frequency response can be studied by performing dynamic simulations of the sudden loss of generation and observing the resulting frequency nadir. If the frequency nadir falls below the limit for under-frequency load shedding in the first few seconds, it can be concluded that there is insufficient inertia in the system to control the frequency excursion within the stipulated limits (see figure 3.5). To determine whether there is a maximum limit for the penetration of “inertia-less” generation, a series of simulations need to be performed, starting with 100 percent penetration, then decreasing penetration levels gradually until the observed frequency nadir ceases to fall below the minimum allowable frequency. To assess the adequacy of the existing primary reserves, determine whether the system frequency can be brought back up to within the stipulated range by a certain time. Scenarios Luzon: Maximum import via high voltage, direct current (HVDC) link and high VRE power generation supplying low demand. Visayas: Maximum import via HVDC link and high VRE power generation supplying low demand. Mindanao: High VRE power generation supplying low demand. Other: Other regions with particularly low cross-island interconnection capacity (high voltage alternating current) may also be studied assuming island mode operation. Model Philippine transmission grid: Acquire full dynamic system models of the region studied. Generator governor models should requirements be included as should be an appropriate dynamic model for the HVDC converters. Wind power generation: Determine aggregated P&Q output of WPP based on fixed wind speed. Wind turbine modelling requirements depend on the assumptions made about the capabilities of the turbines. Option A: No inertia or primary reserve contribution—model new wind generation as doubly fed induction generator (DFIG) turbines with appropriate voltage support capability. Option B: Virtual inertia or primary reserve contribution—appropriate modeling of the offered capability is required. Option C: Inertia contribution caused by direct-coupled wind turbine model—model inertia contribution of existing wind generation as appropriate. Solar PV models: Aggregated P&Q output of solar PV power plant based on fixed irradiance. Assume no inertia contribution. Data Demand: Projected future off-peak demand for all nodes in the network model (maximum and minimum demand in MW). requirements Generation: Projected future installed generation capacity and corresponding availability during off-peak periods (in MW). How to If the simulation results in uncontrollable frequency excursion and load shedding, maximum VRE penetration limits may need interpret to be applied unless further measures are taken. results and This limit, however, is expected to be at quite a high penetration rate. For instance, for the Irish grid it was 60–80 percent. the expected Therefore, a limit might be found, but it is unlikely to be a short-term issue. Therefore, this study could be delayed—keeping in output mind, however, that specific island systems could end up with higher penetration rates than others. At present, the solution to such a problem would be to impose a maximum “inertia-less” generation penetration limit, to ensure that enough synchronous generators are online at all times. However, new developments in wind turbine technologies have been made that offer “virtual inertia” capabilities. Therefore, when higher future penetration rates are expected, virtual inertia capability may be incorporated as a grid code requirement. 3. Study Guide 23 Figure 3.5. Stable and Unstable System Frequency Response Following the Sudden Loss of Generation Primary frequency response Nominal frequency System frequency (Hz) Stable operation Minimum frequency limit 0 5 10 15 20 Time (s) Nominal frequency System frequency (Hz) Insufficient inertia to maintain stability Minimum frequency limit 0 5 10 15 20 Time (s) Primary frequency response Nominal frequency System frequency (Hz) Minimum frequency limit Stable but insufficient for operating standards 0 5 10 15 20 Time (s) Source: Authors. 24 A Guide to Operational Impact Analysis of Variable Renewables: Application to the Philippines To obtain accurate models of the regional networks that the system operator of each grid be involved in the for performing frequency stability studies, it is important study. Stakeholders NGCP, generator owners, wind and solar PV project developers, NREB, DOE, ERC required Key reference Bömer, J., K. Burges, C. Nabe, and M. Pöller. 2010. “All Island TSO Facilitation of Renewables Studies: Final Report for Work studies Package 3,” EirGrid, Dublin. Transpower New Zealand. 2007. “Wind Generation Investigation Project 5: Effect of Wind Generation Capability on Management of Frequency Excursions.” Transpower New Zealand, Wellington, New Zealand. Fast Simulation of Wind Generation for Frequency Stability Analysis in Island Power Systems, James Conroy, 2010-10. Dynamic Simulation Studies of the Frequency Response of the Three US Interconnection with Increased Wind Generation, Berkley National Laboratory, 2010-12. Roam Consulting. 2010. “Assessment of FCS and Technical Rules,” Independent Market Operator,Perth, Australia. 3.4. Fault Level Adequacy for HVDC Link malfunction could be calculated. However, the resources Operation (and Protection Relays) required to perform a full short-circuit study are extensive. The fault level adequacy study investigates whether the Therefore, it is recommended that a general impact study addition of new generation changes the general system be performed first. If the general study indicates that a fault level in such a way that proper HVDC operation is severe impact is likely, then a detailed study should be per- inhibited. This could potentially be an issue if the amount formed to determine the absolute maximum amount of of VRE in Luzon or Visayas causes the general fault level to penetration. fall—the two regions are interconnected with an HVDC The fault current contribution of VRE power plants is link, and this link has been critical for supplying enough highly dependent on their FRT capability. Therefore, the power to meet demand in Luzon. grid code must establish requirements for new and existing The maximum amount of VRE that can be integrated VRE generation for fault ride-through, and must be accu- without causing the HVDC and protection equipment to rately represented in the study. Objective A) Indicative study To assess whether the impact of new VRE installations on the system fault level is likely to be an issue for correct HVDC link operation. B) Maximum VRE penetration study To determine the maximum amount of VRE that can be integrated into the power system without causing the short-circuit ratio of the HVDC link to fall below minimum. Methodology A) Indicative study Steady-state analysis can be performed for different VRE penetration scenarios to assess the general impact on the short- circuit level at the terminals of the HVDC link. B) Maximum VRE penetration study Electromagnetic time domain transient simulations can be performed for balanced and unbalanced short-circuit faults at particular points in the network, such as the connection point of the WPP or at the terminals of the HVDC device. (continued) 3. Study Guide 25 Scenarios High wind and solar PV development. Series of interconnector capacity levels. Short-circuit current is normally provided by conventional synchronous generators. Therefore, the worst case scenario is a low load situation in which most conventional generation is displaced by wind generation. HVDC-LUZON: High wind power generation supplying low demand. HVDC-VISAYAS: High wind power generation supplying low demand. Model A) Indicative study requirements Luzon and Visayas transmission grid: AC power flow model with the existing topology and typical operating scheme (open breakers and the like). Wind power generation: Aggregated P&Q output of WPPs based on fixed wind speed for high and low wind power outputs. Solar PV power generation: Aggregated P&Q output of solar PV power plant based on fixed solar irradiation for high and low solar PV power output. Other generation: P&Q model with full availability corresponding to the time point analyzed, including external reactive power devices. B) Maximum VRE penetration study Electromagnetic model of WPP and connection point with equivalent grid representation. Data Demand: Projected future off-peak demand for all nodes in network model (maximum and minimum demand in MW). requirements Generation: Projected future installed generation capacity and corresponding availability during off-peak periods (in MW). How to If the simulation results show that the short-circuit ratio at HVDC terminals will fall below minimum operating requirements, interpret maximum VRE penetration limits may need to be imposed unless further measures are taken. This outcome is highly results and dependent on the FRT capability and short circuit current contribution characteristics of the VRE. This situation is known the expected in general to lower the fault level (Bömer and others 2005; Transpower New Zealand 2008), but in some cases it may even output increase the fault level (figure 3.6). Therefore, careful observation is required using accurate models of the type of VRE that will be installed. The most common solution for preventing fault level reduction from affecting HVDC operation is to implement an operation limitation such as a minimum-must-run generation unit. The protection equipment might need to be redesigned so that it functions properly with the new fault level. The system operator of each region, as well as the opera- study to ensure that accurate models of the regional grids tors of WPPs and the HVDC link, must be involved in the are obtained for performing fault level studies. Stakeholders NGCP and its system operators, WPP owner, HVDC link operator required Key reference Bömer, J., K. Burges, C. Nabe, and M. Pöller. 2010. “All Island TSO Facilitation of Renewables Studies: Final Report for Work studies Package 3,” EirGrid, Dublin. Transpower New Zealand. 2008. “Wind Generation Investigation Project 9: Effect of Wind Generationon Reactive Power Contribution and Dynamic Voltage Responses.” Transpower New Zealand, Wellington, New Zealand. Wind Power Plant Short Circuit Current Contribution for Different Fault and Wind Turbine Topologies, V. Gevorgian, et al., NREL, 2010–10. 26 A Guide to Operational Impact Analysis of Variable Renewables: Application to the Philippines Example of Different Wind Power Penetration Levels (0, 25%, 50%, 75% 100%) on the Figure 3.6.  Three-Phase Faults at Selected Bus Bars in Ireland (Around Each Average Value the Minimum and Maximum Short Circuit Currents Over 63 Load Cases are Indicated by the Error Bar) max 50 limit W0 W25 W50 W75 W100 45 40 limit 220 kV 35 30 limit 110 kV kA 25 20 15 10 5 /”5’1”/”6 1”/”6’==;’MN 1”/”6’AA;’MN 0 SHANNONB SRANANAG AGANNYGA BALLYLIC BALLYWAT BINBANE CLONKEEN GLENLARA KILKENNY LETTERKE RATRUSSA SLIGO TRALEE BAFD1- OMAH1- DUNSTOWN MNYPG1 WOODLAND BAFD2- AGHADA ARKLOW FINGLAS FLAGFORD INCHICOR KNOCKRAH LOUTH RoI NI RoI RoI NI 380 275 220 110 Source: [15], page 53. 3.5. Reserve Adequacy for Expected Forecast Errors10 • secondary reserves for regulation (1–5 minutes), and The types of reserves that exist, and how they are deter- • tertiary reserves for balancing (5–30 minutes). mined, often differ between power systems, making it chal- lenging to apply a general methodology. However, some These reserves are often determined and acquired papers (Holttinen, Milligan, and others 2012; Holttinen, through ancillary service contracts or the ancillary services Meiborn, and others 2009; Soder and Holttinen 2008) market; however, systems with short gate closure times like attempt to bridge the gap, and methodologies presented the Australian NEM (5 minutes) handle the task of ensur- in this section are drawn from their findings. Many studies ing adequate reserves in the dispatch market, and only need also attempt to calculate the percentage increase in reserves to secure reserves for frequency regulation. required to integrate a certain amount of VRE, as well as the In the Philippines, both types of reserves are covered associated costs. by the secondary response of load following and frequency For the reserve adequacy study, at least two reserve regulating reserves. (Refer to figure 2.6 and table A1 in types should be studied. (According to the definition of appendix A for definitions.) The requirement for load fol- reserves in the Philippines, more types may need to be lowing and frequency regulating reserves is set equal to assessed.) The two minimum types are the average load forecast variance (4 percent in Luzon) 10. Impacts from “expected forecast errors” are part of normal operation, that is, non-event cases. Impacts from unexpected events (contingency and event reserve) are assessed in the study in the next section. 3. Study Guide 27 (Philippine Wholesale Electricity Spot Market 2004). variance of the net load.11 The additional reserves required However, because the addition of VRE will compound the to cover the integration of VRE can then be calculated as level of uncertainty, the reserve requirement should also the difference between the standard deviations of the net take into account the variance of the VRE output. load and the load, multiplied by some factor to achieve the Two methods are commonly used to evaluate the required confidence level. reserve requirement—the statistical method and the con- The convolution method involves evaluation of prob- volution method. ability density distributions for VRE and load variability The statistical method involves the evaluation of load and associated uncertainties. These are then superimposed and generation output variability and forecast errors. The by convolution to find the magnitude and frequency of all variances of these components are summed to find the potential imbalances. 11. Net load is demand minus VRE power output. Objective A) Maximum VRE penetration study To determine the maximum amount of VRE that could be integrated into the power system without needing to increase the load following and frequency regulating reserves. B) Assessment of reserve requirements To assess the load following and frequency regulating reserves required to integrate high levels of RES-E advocated by government policies. Methodology The statistical method for evaluating the reserve requirements is recommended because of its simplicity. Historical demand profiles scaled to future demand levels and a reproduction of VRE output profiles based on historical weather data (for example, wind speed, solar radiation) are required. Reproduction of future demand and VRE power outputs on 1-minute or 5-minute basis is recommended. Calculate the net load by subtracting the VRE power output from time-correlated demand, and find the statistical variance of the net load. According to the methodology currently applied in the Philippines, the average variance is the required amount of reserve. However, to make sure that the required reserves allow the system operator to meet reliability standards, a more detailed method may need to be used. Forecast values and resulting forecast errors, as well as forced outages, can also be included in this analysis to capture all types of uncertainty of load, wind, and other production. Additionally, the associated costs of each scenario can be calculated for comparison. Scenarios The reserve requirements for at least two scenarios should be evaluated for comparison for each island. Base Case: without VRE development. VRE Integration Case: with VRE. If desired, a number of scenarios could be developed, with varying degrees of VRE integration. Interconnector Sensitivity (Optional): to compare the regulation reserve requirements for different interconnector use strategies. For example, base load could be covered by interconnector imports to free up generation that can provide reserves. Model Wind and solar PV power plant output models that can estimate the active power output based on wind speed and solar requirements radiation data. Data Demand: Normal historical demand for one year on a 1-minute or 5-minute basis, scaled to future demand level. requirements Wind and solar PV generation: Generation output on a 1-minute or 5-minute basis, calculated from historical wind speed and solar radiation time series data synchronized with demand at the expected installation locations. How to If the reserve requirement WITH VRE exceeds the requirement for load only, maximum VRE penetration limits may need to interpret be imposed unless further measures are taken. results and Energy penetration rates of about 10 percent are expected to have virtually no impact on the regulating reserves. Therefore, the expected in Luzon and Visayas, where average energy penetration will be less than 10 percent (resulting in an instantaneous maximum output penetration level of 35 percent), the impact on reserve requirements will be marginal. 28 A Guide to Operational Impact Analysis of Variable Renewables: Application to the Philippines To model the outputs of wind and solar PV power developers, organizations that have extensive weather data, plants accurately, a good understanding of the planned loca- such as the bureau of meteorology, should be consulted, as tions of the power plants is required, along with detailed should be renewable energy advocates. wind speed and irradiance. In addition to the generation Stakeholders NGCP, NREB, renewable energy advocates, renewable generation project developers, wind speed measurement providers, required solar irradiation measurement providers Key reference General: studies Holttinen, H., M. Milligan, E. Ela, N. Menemenlis, B. Rawn, R. Bessa, D. Flynn, E. Gomez-Lazaro, J. Dobschinski, and N. Detlefsen. 2012. “Methodologies to Determine Operating Reserves due to Increased Wind Power.” IEEE Transactions on Sustainable Energy, no. Special Issue: Wind Energy. Holttinen, H., P. Meibom, A. Orths, F. van Hulle, B. Lange, M. O. O’Malley, J. Pierik, B. Ummels, J. O. Tande, A. Estanqueiro, M. Matos, E. Gomez, L. Söder, G. Strbac, A. Shakoor, J. Ricardo, C. J. Smith, M. Milligan, and E. Ela. 2009. “Design and Operation of Power Systems with Large Amounts of Wind Power.” Final report, IEA WIND Task 25, Phase one 2006-2008. VTT Tiedotteita, Helsinki. Milligan, M., P. Donohoo, D. Lew, E. Ela, B. Kirby, H. Holttinen, E. Lannoye, D. Flynn, M. O’Malley, N. Miller, P. Børre Eriksen, A. Gøttig, B. Rawn, M. Gibescu, E. Gómez Lázaro, A. Robitaille and I. Kamwa. 2010. “Operating Reserves and Wind Power Integration: An International Comparison.” National Renewable Energy Laboratory (NREL), Golden, Colorado. USA: EnerNex Corporation. 2011. “Eastern Wind Integration and Transmission Study,” National Renewable Energy Laboratory, Golden Colorado. GE Energy. 2010. “Western Wind and Solar Integration Study,” National Renewable Energy Laboratory (NREL), Golden, Colorado. GE Energy. 2008. “Analysis of Wind Generation Impact on ERCOT Ancillary Services Requirements.” GE Energy, New York. Quebec: Dernbach, M., D. Bagusche, and S. Schrader. 2010. “Frequency Control in Quebec with DFIG Wind Turbines,” in 9th International Workshop on Large-Scale Integration of Windpower into Power Systems/Transmission Networks for Offshore Wind Power Plants, Quebec City. Kamwa, I., A. Heniche, and M. de Montigny. 2009. “Assessment of AGC and Load-Following Definitions for Wind Integration Studies in Quebec.” energynautics, Langen, Germany. de Montigny, M., A. Heniche, I. Kamwa, R. Sauriol, R. Mailhot, and D. Lefebvre. 2010. “A New Simulation Approach for the Assessment of Wind Integration Impacts on System Operations,” 9th International Workshop on Large Scale Integration of Wind Power and on Transmission Networks for Offshore Wind Farms, pp. 460–67, Quebec City, October 16–17. Hawaii: Miller, N., D. Manz, H. Johal, S. Achilles, L. Roos, and J. P. Griffin. 2010. “Integrating High Levels of Wind in Island Systems: Lessons from Hawaii,” in International Conference on Sustainable Energy Technologies, pp. 1–8, December. Ireland: Sustainable Energy Ireland. 2004. “Operating Reserve Requirements as Wind Power Penetration Increases in the Irish Electricity System.” Sustainable Energy Ireland, Dublin. Western Australia: Roam Consulting. 2010. “Assessment of FCS and Technical Rules,” Independent Market Operator, Perth, Australia New Zealand: Transpower New Zealand. 2007. “Wind Generation Investigation Project 5: Effect of Wind Generation Capability on Management of Frequency Excursions.” Transpower New Zealand, Wellington, New Zealand. 3. Study Guide 29 3.6. Reserve Adequacy for According to the presentation by DoE, however, for Extreme Ramps Visayas and Mindanao, the largest units are about 100 This reserve adequacy study investigates whether there are MW, whereas the largest proposed WPP is 122 MW (in enough primary and tertiary event reserves (correspond- Visayas). Therefore, the primary reserve requirement for ing to contingency spinning and backup reserves in the these regions will possibly need to be changed. Philippines) for supply to meet the expected load when More challenging is the tertiary reserve. According to VRE is added to the system. Event reserve refers to spinning Holttinen, Milligan, and others (2012), compensating for reserves for contingency response and backup reserves large but slow events, corresponding to forecast errors for replacing other reserves, as well as reserves to deal with 10 minutes to some hours ahead, is the most challeng- slow contingency events (such as weather-induced ramps) ing based on international studies. Furthermore, extreme (refer to figure 2.6 and table A1 in appendix A for defini- ramping caused by weather or market events may be caused tions). These reserves are often determined and acquired specifically by the introduction of VRE. through the ancillary services market, or through direct Currently, the only tertiary reserve in the Philippines instruction (must-offer); however, markets with short dis- is for replacement of the contingency reserve, called patch times such as the Australian NEM (5 minute) han- the “backup reserve.” There are no reserves that can be dle tertiary reserves in the dispatch market, and are not as deployed between regulating reserves (25 seconds to 30 concerned. minutes) and market dispatch (1 hour). In the Philippines, contingency reserve is defined as For a slow contingency event that becomes apparent reserve equivalent to the largest loss of supply that could be in advance, such as the approach of a storm front, a loss of caused by disconnection of the largest online generation power in less than 1 hour12 could potentially be a problem unit or by the outage of a circuit. because neither regulation reserve nor primary contin- Presently, the largest unit in Luzon is a gas unit of about gency reserve is designed to cover for this additional loss. 1,200 MW, while the largest expected VRE plant is a WPP Rather than adding this potential loss to costly spinning of less than 150 MW. Thus, integration of the WPP will not reserve, whether regulating reserves would be adequate to require an increase in primary reserve. Even in the worst cover this kind of event should be examined, and creation case—for example, none of the WPPs are equipped with of a new reserve category might even be considered. FRT capability and trip off in the event of a voltage dip— To find the maximum VRE level that does not cause the largest aggregation of VRE in one region (northern such a situation, historical weather events should be stud- Luzon) is expected to be less than 350 MW. Therefore, ied and the maximum ramp rate should be compared with it is unlikely that the reserve requirement will need to be existing reserve requirements. changed. 12. Dispatch is one hour, and regulating reserve has the capability to come online in 30 minutes. 30 A Guide to Operational Impact Analysis of Variable Renewables: Application to the Philippines Objective To determine the maximum amount of VRE that could be integrated without the need to increase regulating reserves. Methodology Review historical weather data and determine probable “worst case” scenario that results in maximum ramping of wind power output in northern Luzon, and solar PV power wherever large installations are planned. Estimate the maximum wind (or solar) generation change event in the high VRE penetration scenario based on the weather data. For dispatch and short-term capacity reserves, perform market dispatch simulations. Scenarios The reserve requirements for at least two scenarios should be evaluated for comparison for each island. Base Case: without VRE development. VRE Integration Case: with VRE. If desired, a number of scenarios could be developed, with varying degrees of VRE integration. (Start with maximum and reduce until the limit is found.) On- and off-peak demand scenarios with high VRE penetration, in which the minimum number of units providing reserves are online. Model Philippine transmission grid: Dispatch model requirements Wind and solar PV power generation: WPP and solar PV power plant output model that can estimate the active power output based on wind speed and solar radiation data. Models may include advanced capabilities such as active power reduction and delta control. Capability of conventional units: Ramp rates, start-up, shut down, fuel costs, and so forth. Data Data based on a real event: 5-minute wind power and solar PV output corresponding to wind speed and solar irradiation requirements during the actual extreme weather event identified. Corresponding load data and generation availability at the time of the event. Demand: Historical demand for a period that includes extreme weather events on a 1-minute or 5-minute basis, scaled to future demand level. Wind and solar PV generation: Generation output on a 1-minute or 5-minute basis, calculated from historical wind speed and solar radiation time series data synchronized with demand at the expected installation locations. How to If the reserve requirement with VRE exceeds the requirement for load only, maximum VRE penetration limits may need to be interpret imposed unless further measures are taken. results and It is expected that a slow ramp event in Luzon will have an impact on regulating reserve. However, rather than limiting VRE, it the expected may be advisable to revise the regulating reserve requirement definition or create a new type of ancillary service. The benefit of output allocating interconnector capacity for transfer of reserves may also be explored. To model the weather impact on power plant outputs Furthermore, to represent the services offered by gener- accurately, a good understanding of the planned location ators and their operation capabilities accurately, it is impor- of WPPs and solar PV plants is required , along with the tant to involve both renewable and conventional power characteristics of the generation technology employed, generators. For example, for some studies in the United and the type of weather events experienced in that region. States, industry representatives have complained that the In addition to the generation project developers, organiza- operational capability of conventional generators has been tions that have extensive weather data, such as the bureau overestimated and costs underestimated, so that the results of meteorology, should be consulted. Renewable energy do not adequately reflect the true effort required to inte- advocates such as the Clean Energy Council should also be grate VRE generation. By the same token, the frequency consulted. regulation capabilities that can be offered by WPPs and solar PV inverters must also be taken into consideration. Stakeholders NGCP, NREB, renewable energy advocates, renewable generation project developers, conventional generator owners, weather required bureau, wind speed measurement providers, solar irradiation measurement providers, VRE output forecasters, DOE, ERC Key reference GE Energy. 2008. “Analysis of Wind Generation Impact on ERCOTAncillary Services Requirements.” GE Energy, New York. studies Piwko, R., X. Bai, K. Clark, G. Jordan, N. Miller, and J. Zimberlin. 2005. “The Effects of Integrating Wind Power on Transmission System Planning, Reliability, and Operations,” GE Energy, New York. 3. Study Guide 31 3.7. Treatment of Wind Power in Long- locations in which WPPs and solar PV plants still do not Term Reliability Assessment exist, the outputs will have to be estimated based on wind When VRE power begins to replace retiring conventional speed and solar irradiance data. Therefore, such data must generation instead of being added to existing capacity, be collected early on, and providers of such data must be VRE’s capacity contribution to reliability must be assessed made part of the study. so that long-term reliability standards are not breached. It is also important to consider the impact of hydro Reliability metrics are the best tool for accurately calculat- generation, particularly in systems with significant shares ing the capacity credit (dependable capacity) of wind and of hydro power, as in the Philippines. Generation adequacy solar PV power. must be assessed for both reliability and power, and must For such a study, extensive load, wind power, and solar take into consideration dry periods, not limiting the study power output data on an hourly basis are required. In to high and peak demand periods. Stakeholders NGCP, NREB, wind speed measurement providers, solar irradiation measurement providers, generator owners, DOE, ERC required Key reference Holttinen, H., P. Meibom, A. Orths, F. van Hulle, B. Lange, M. O. O’Malley, J. Pierik, B. Ummels, J. O. Tande, A. Estanqueiro, M. studies Matos, E. Gomez, L. Söder, G. Strbac, A. Shakoor, J. Ricardo, C. J. Smith, M. Milligan, and E. Ela. 2009. “Design and Operation of Power Systems with Large Amounts of Wind Power.” Final report, IEA WIND Task 25, Phase one 2006-2008. VTT Tiedotteita, Helsinki. A Review of Different Methodologies Used for Calculation of Wind Power Capacity Credit, L. Söder, et al., KTH, 2008. Milligan, M., and K. Porter. 2008. “Determining the Capacity Value of Wind: An Updated Survey of Methods and Implementation.” NREL, Golden, Colorado. Valuing the Capacity of Intermittent Generation in the South-west Interconnected System of Western Australia, REWG WP2, IMO (MMA) 2010-01. Supplementary Analysis of Capacity Valuation, REWG WP2, IMO (MMA) 2010–04. Analysis of Procedures for Assessing the Capacity Value of Intermittent Generation in the Wholesale Electricity Market, REWG WP2, IMO (MMA) 2010-08. 3.8. Electromechanical Impact Another potential concern occurs if the VRE power When VRE power begins to displace synchronous gen- plants are expected to be connected by series-compensated eration in significant proportions (above 80 percent) to lines or HVDC devices because of their remote location supply load (as in Spain, Portugal, and Ireland today), it is (that is, offshore). Subsynchronous interaction with certain possible that the electromechanical characteristics of the types of wind turbine generators and converter electron- system will change. This may cause the system oscillatory ics has been discovered to potentially interact with series mode to change, rendering inadequate the system damp- compensation and HVDC electronics resulting in sig- ing and power system stabilizer settings. To investigate nificant damage, as demonstrated by the event in ERCOT. this possibility, modal analysis by eigenvalue calculation Therefore if such situations are foreseen, investigation may of small-signal stability with and without VRE would need be warranted. to be evaluated and compared. This analysis was done in VRE impact on transient stability has been studied in the studies by Transpower, ENTSO-E and the European DENA and some others, but no significant impact has Commission (2010), and the “All Island Facilitation of been observed. VRE generation is normally connected via Renewables”, but all of them reported that no significant inverters, which do not interfere with the electromechanics impact was observed for the particular renewable scenarios of the system directly, so no impact is expected. studied. 32 A Guide to Operational Impact Analysis of Variable Renewables: Application to the Philippines Stakeholders Market operator, system operators, HDVC owners required Key reference Small-signal study studies Effect of Wind Generation on Small Signal Stability, WGIP Investigation 8, Transpower NZ, 2008–03. Bömer, J., K. Burges, C. Nabe, and M. Pöller. 2010. “All Island TSO Facilitation of Renewables Studies: Final Report for Work Package 3,” EirGrid, Dublin. ENTSO-E and European Commission. 2010. “European Wind Integration Study (EWIS): Towards A Successful Integration of Large Scale Wind Power into European Electricity Grids,” Brussels. Subsynchronous Interaction Study CREZ Reactive Power Compensation Study, ERCOT (ABB), 2010–12. The Impact of Wind Farms on Sub Synchronous Resonance in Power Systems, Elforsk (Gothia Power), 2011-04. Sub Synchronous Interactions with Wind Farms Connected Near Series Compensated AC Lines, A. K. Jindal, et al., 2010–10. 4. Conclusions The aim of this report is to show what kind of system-wide • The need to ensure sufficient inertia in the system studies should be carried out in the Philippines to assess the to avoid frequency diversions. System-wide general impacts of variable renewable energy (VRE) and to deter- impact studies can be performed, which may lead to a mine whether limits need to be imposed on the level of hard operating limit, such as the minimum number of integration. The report is based on a review of international synchronous generators that must be online at any one experience in studying and dealing with VRE integration. time. Furthermore, VRE power plants can be asked to The types of issues that are of particular concern to VRE contribute to inertia using virtual inertia technology. integration, especially for small island systems like those of • The need for adequate fault levels for correct opera- the Philippines, were found to be the following: tion of HVDC devices and protection equipment. • The need to build up transmission capacity to evacuate System-wide general impact studies can be performed VRE power, which is often in remote areas of the net- first; if issues are foreseen, detailed studies can be car- work, and the importance of robust grid design to deal ried out. Detailed short-circuit studies must be carried with the potential rapid expansion of VRE generation out as part of the connection studies for individual VRE capacity. Robust designs can be developed based on power plants. a variety of scenario studies as part of long-term plan- • The ability of the system to balance supply with demand ning, and including an assessment of extreme weather even with the additional uncertainty introduced by impacts is vital. VRE power. The amount of reserves required can be • The need to implement voltage support measures such estimated using statistical methods based on historical as fault ride-through requirements on VRE power data, or evaluated in detail by simulation of operation plants. Some geographical areas depend on the voltage processes (pre-dispatch, dispatch, and ancillary ser- profile of the grid and the support capability of other vice operation). The statistical approach is simpler but synchronous generation units. The most common, less accurate, and large amounts of detailed data are and therefore the recommended way to reduce nega- required for either approach. Therefore, the necessary tive impacts, is to establish performance requirement rigor of the study depends on the level of security and standards for VRE power plants. Requirements can be reliability required. implemented most effectively through the grid code. • When high penetration is anticipated, it is important to In addition, voltage support can be obtained from the ensure that the installed generation capacity can meet grid by installing external reactive power devices, or by long-term reliability standards. The process for calcu- soliciting additional reactive power services from syn- lating the VRE contribution to reliability is compli- chronous generators (for example, requesting them to cated and involves extensive data (more than 10 years). operate in synchronous condenser mode). Therefore, it is important to begin collecting data as early as possible, even if high penetration levels are not expected for a long time. 33 34 A Guide to Operational Impact Analysis of Variable Renewables: Application to the Philippines • When high penetration is anticipated, investigations The current level of VRE in the Philippines is very low into electromechanical stability may need to be car- compared with many other systems around the world, ried out in addition to thermal, voltage, and frequency and international experience has shown that the observed impact studies. This includes studies of small-signal impacts of VRE are minor up to about 20–30 percent pen- impact and subsynchronous interactions. etration. Thus, the Philippines will be able to prepare and • When particular configurations result in certain wind carry out the types of studies recommended in this report turbines being connected via series-compensated lines, in parallel with installation of VRE power plants, and can there is a need to check for SSI. start applying changes to the grid structure, grid code, mar- ket structure, and policy framework to be able to cope with higher VRE penetration in the future. AppendiXes Appendix A. Definition of Balancing and Reserves The goal of power system operation is to balance supply can be broken down into broad categories of a few seconds and demand at all times while maintaining reliability and (governor), 1–5 minutes (automatic generation control system security standards. Given the few options for stor- and regulation), 5–30 minutes (dispatch or load follow- ing electricity in a modern power system, the objective is to ing), and 30 minutes to some hours (replacement and produce energy at the instant that it is consumed (or shed supplementary reserve). These categories are highlighted load when necessary). To facilitate this process in the most in orange in figure A1, and these terms are described in efficient manner possible, the system operator optimizes table A1 the use of available resources (where electricity markets are The definitions of different types of reserves vary in operation, often through markets), under a set of trans- depending on the power system. Some of the common mission constraints, to meet the electricity consumption terms used are shown in table A1. For the purposes of this forecasted at a certain point ahead of time. The time lag report, the terms primary, secondary, and tertiary reserves between the forecast schedules and delivery in this process are used. Figure A1. Time Scale for Different Operation Mechanisms and Reserves Seconds Minutes Hours-Days Months-Years Stability Balancing Adequacy Intertial AGC & Dispatch Replacement Scheduling response and Regulation (Load- and (Maintenance Governor following) Supplementary planning) reserve Primary Secondary Tertiary Reserve Reserve Reserve Source: Authors. 37 38 Appendixes Table A1. Reserve Categories Name Use Common Terms Contingency reserve Capacity available for assistance in active power balancing during Contingency reserve, disturbance infrequent events like power plant outages that are more severe than reserve, N−1 reserve balancing needed during normal conditions and are used to correct instantaneous imbalances Primary reserve for Portion of contingency reserve that is automatically responsive Primary control reserve, frequency contingency response to instantaneous active power imbalance and stabilizes system responsive reserve, governor droop, frequency (primary) and returns frequency to nominal (secondary) secondary control reserve, spinning reserve. automated generation control Non-event reserve Capacity available for assistance in active power balance during Non-event reserve normal conditions, or those that occur continuously (no faults in system) Secondary reserve for Capacity available during normal conditions for assistance in Regulating reserve, regulation, load regulation active power balance to correct the current imbalance, is faster frequency control, primary/secondary than economic dispatch optimization, is random, and requires an control automatic centralized response Tertiary reserve for balancing Capacity available during normal conditions for assistance in active Load following, following reserve, power balance to correct a future anticipated imbalance, does not tertiary reserve, minute reserve, require an automatic centralized response schedule reserve, dispatch reserve, balancing reserve Event reserve (slow reserve) Capacity available for assistance in active power balance during infrequent events that are more severe than balancing needed during normal conditions Tertiary reserve for slow Capacity available for assistance in active power balance during Ramping reserve, supplemental reserve, contingency events infrequent events that are more severe than balancing needed balancing reserve during normal conditions and is used to correct non-instantaneous imbalances Tertiary reserve for replacing Portion of contingency reserve that is available for assistance in Tertiary control reserve, replacement primary and secondary replacing frequency responsive reserve (primary and secondary) reserve, supplemental reserve, reserves used during a severe instantaneous event so that it is available for a balancing reserve subsequent instantaneous event that occurs in the same direction. Can also be used and dimensioned to include slower ramping events like large forecast errors. Source: Holttinen, Milligan, and others 2012, 2. Appendix B. Summary of International Experience A multitude of studies are available in the international up wind and solar PV energies promoted by government domain that assess the impact of variable renewable energy policies to meet national or state renewable energy (RE) (VRE) integration from a purely technical standpoint, an targets. To achieve RE targets set by governments, systems economic standpoint, and anywhere in between. To ensure must adapt; therefore, most studies assess the impact that the reliability and security of the power system, these stud- a certain percentage of VRE integration is likely to have on ies may propose technical solutions such as either hard the system. See table B1. limits or soft limits, depending on the operation regime, Based on such studies, measures to accommodate VRE and may outline possibilities for increasing the limits by are developed and decisions are made about how best enhancing the capability of the system and its components. (most efficiently) to implement those decision. The deci- The decision about the limit to impose and to what degree sions are based on the ability of the system to implement the existing system should be modified to accommodate the solutions and allocate the associated costs, as well as the VRE will most certainly depend on economic priorities ability of the grid operators and renewable energy develop- and on the capabilities of the stakeholders involved. ers to adjust to new operational practices. B.1. Study Objectives B.2. Types of Impacts Studied The objective of a VRE integration study could be to deter- Issues considered in these studies are not particularly mine the maximum allowable wind power penetration unique to VRE; rather, they are the same studies that would that requires no major changes to existing infrastructure be performed for the addition of any new generation. The requirements and operating procedures. Often, however, range of studies can be seen in figure B1. the main driver for VRE impact studies is an effort to scale Table B1. Objectives of Various International VRE Integration Studies Study Objective Reference International Study Maximum generation capacity Minnesota Dispersed Renewable Generation Transmission Study that can be installed without (Minnesota Transmission Owners 2008): violating limits How to distribute 600 MW of wind and biomass power from 42 sites across five planning zones within the state of Minnesota. System impacts of a certain Europe percentage of VRE integration European Wind Integration Study, 34 percent penetration (wind power/(minimum load + I/C)) (ENTSO-E and European Commission 2010) All Island Grid Study (Ireland), 178 percent penetration DENA Grid Study (Germany), 71 percent penetration (DEWI and others 2005) Denmark, 51 percent penetration (Eriksen and Orths 2008) Red Electrica España, 73 percent penetration (Rodríguez-Bobada and others 2006) United States Western Wind Integration Study, 35 percent penetration (energy penetration) (GE Energy 2010) Eastern Wind Integration and Transmission Study, 30 percent penetration (energy penetration) (EnerNex Corporation 2011) ERCOT Ancillary Services Requirements Study (Texas), 23 percent penetration (GE Energy 2008) New York Independent System Operator, 17 percent penetration (Piwko and others 2005) Hawaii, 96 percent penetration (Miller and others 2010) Oceania Wind Generation Investigation Project New Zealand, 75 percent penetration Future wind generation in Tasmania study (Australia), 95 percent penetration (Transend 2009) Source: Authors. 39 40 Appendixes Figure B1. Issues investigated in VRE integration studies Short- Tertiary reserve Generation term (Load adequacy Secondary system wide scheduling following, reserve (Long-term (Outage balancing) (AGC & Balancing reliability) & hydro storage regulation) Primary planning) reserve Market dispatch (Governor) & Small-signal S Inertia stability response al (Electromechanical Grid adequacy oscillation) (N-5 contingency & congestion) regional Transient Planning Stability response Sub synchronous (Rotor angle & interaction voltage) & F ault Fault level l el Voltage control Power Quality local (Short-circuit (Sh current) (Flicker & Harmonics) years 1 month 1 day 1 1 min 1s 100 ms 10 ms 1 ms Time-constant/Period time Source: Authors. However, because of the nature of VRE power, its interconnector—whichever causes the largest discrepancy impact on particular system issues is higher than on others. between supply and demand as a transient event. The characteristics of the power system under consider- Based on international experience, the conclusion is ation also affect the issues that would be more susceptible that the impact of VRE on primary reserve requirements to impacts from VRE. Thus, certain types of studies are is negligible because the introduction of new VRE power more relevant for VRE integration. The results of these plants generally does not change the size of the single larg- studies are summarized in the following pages. est contingency,14 assuming a fault ride-through (FRT) capability is available from the VRE power plants. If the Balancing13 VRE plants are not equipped with FRT capability, a volt- age dip may cause a group of plants in one area to trip and Primary Response and Contingency Reserve become the largest contingency. Primary response contingency reserves are gener- Wind power outputs do not change fast enough to con- ally designed to cover the largest single contingency stitute a contingency event in normal operation because of event in a system, typically caused by the sudden dis- the mechanical structure of wind power plants (Holttinen connection of a generating unit, a load block, or an 14. The largest contingency depends on the power system. However, according to the presentation by DoE (2011), for Visayas and Mindanao, 13. Different definitions for balancing mechanisms and reserves are used the largest units are about 100 MW, whereas the largest proposed WPP in different power systems. Refer to appendix A for the definitions of is 122 MW (in Visayas). Therefore, it is possible that the primary reserve primary, secondary, and tertiary reserves used in this report. requirement needs to be changed for these regions. Appendix B. Summary of International Experience 41 Milligan, and others 2012). However, solar PV power out- it is crucial that reserve adequacy be assessed based on the put is a more direct energy conversion technology and can type of forecast errors likely to be experienced. experience higher ramp rates. Furthermore, the impact At high VRE penetration levels, the aggregated variabil- of certain weather events, such as a storm front hitting a ity and forecast error can potentially result in large but slow cluster of wind power plants, may need to be considered contingency events. For example, a large cloud or storm depending on the system characteristics. front could be expected to sweep across a solar PV plant or a wind power plant, respectively, causing a large discrep- IMPORTANT FOR: ancy in expected supply and demand, but there could still • Systems with large VRE plants in concentrated be time to secure reserves. Therefore, it is important to areas identify these types of contingency situations based on the power system and assess the adequacy of corresponding STUDIED IN: reserves. • Portugal: Discovery that group of wind power plants tripped when there was a voltage dip led to the review of FRT in grid code IMPORTANT FOR: • Systems with high VRE penetration displacing synchronous generation Secondary Response for Frequency Regulation • Isolated systems with weak interconnection to VRE power’s most significant impacts on balancing affect neighboring systems (i.e. island systems) “non-event” reserves, that is, regulation reserves (1–3 min- • Systems with wind turbine generators connected utes) and load-following or market dispatch reserves (10– via series compensated lines 30 minutes). The impact on regulation reserves is lower STUDIED IN: compared with the impact on load-following reserves, • Ireland: Minimum system inertia requirement has however, because VRE power output forecasts improve the been implemented closer they are to real-time dispatch. • ERCOT: SSI has been observed on series com- Therefore, the impact on secondary reserves is highly pensated line dependent on forecast accuracy and on how forecasts are considered in the scheduling and dispatch of regulation resources.  Stability Ramp rates for wind power are still typically much lower than demand ramping rates (Holttinen, Milligan, IMPORTANT FOR: and others 2012); therefore, a system that can adequately • Systems with high VRE penetration and weakly deal with demand ramping should also be able to accom- interconnected for frequency support modate VRE ramping.15 STUDIED IN: • ERCOT: every 1 minute; every 5 minutes Tertiary Reserves for Balancing and “Slow Contingency” Events Electromechanical Stability Systems that balance supply and demand between gate Assess the impact on system inertia, transient response closure time for market dispatch and regulation with some rotor-angle stability, small-signal oscillatory stability, and form of tertiary reserve16 experience the largest impacts subsynchronous interaction. from VRE power output forecast errors. For such systems, The direct electromechanical impact of VRE is likely to be low (especially at low penetration) because most VRE power generators are connected via converters and are 15. No studies into system-wide solar PV ramp rates have been found. decoupled from the power system. The impact on system Based on data from large plants on individual sites, solar PV ramp rates are much faster than wind ramp rates. Solar ramp rate characteristics inertia is also likely to be low, except when VRE penetration would need to be studied separately. 16. As in the United States, where there is unit commitment reserves. 42 Appendixes is high17 and VRE generation displaces a significant num- IMPORTANT FOR: ber of online synchronous generators. This situation is • Systems with high VRE penetration and weakly more likely to occur in small and isolated systems, for which interconnected for frequency support electromechanical coupling to the neighboring network is weak. Furthermore, subsynchronous control interaction STUDIED IN: has been observed in some systems in which certain wind • ERCOT: every 1 minute; every 5 minutes turbine converters are connected via series-compensated lines. Fault Level Adequacy for Operation of Protection Equipment and HVDC When there is a short-circuit fault in a power system, pro- IMPORTANT FOR: tection equipment detects the fault current and isolates the • Systems with HVDC lines fault location for a certain time to clear the fault. When a STUDIED IN: VRE power plant is added to the system, its contribution to • Ireland and New Zealand: General impact on the fault current generally decreases the overall fault level, system fault level was studied and it is possible that the new fault level is beyond the range detectable by the protection equipment. Similarly, the fault Voltage Stability level at the terminals of HVDC devices may drop below Assess the impact of large disturbance (fault ride-through the level necessary for correct operation. The higher the and post fault recovery), small variations (voltage control VRE penetration, the fewer conventional generators will ancillary service, set point control, and dynamic reactive be online to contribute to fault current, thereby exacerbat- power support: ing the risk. The impact of VRE on voltage stability depends primar- ily on the reactive power capability of two constituents, the IMPORTANT FOR: VRE power plant, and the network to which the plant is • Systems with high VRE penetration displacing connected. The degree to which a VRE power plant should synchronous generation contribute to voltage stability is usually dictated by a grid • Systems that are weakly interconnected for volt- code, which may be common to all technology categories age support (as in Europe); specific to technology categories; or spe- STUDIED IN: cific to each installation (as in Australia). Once the VRE • Spain/Portugal: FRT requirements were revised in power plant has fulfilled its obligations, the remaining sup- Grid Code based on voltage stability studies port must be secured from the system, from either external reactive power devices or other conventional generators. Long-Term Planning The higher the VRE penetration, the fewer conventional generators will be online to offer voltage support; therefore, IMPORTANT FOR: grid code requirements and system design must be based • Systems with VRE at remote areas of the network on accurate simulations of expected VRE power plant STUDIED IN: behavior and system behavior. • ERCOT: Transmission infrastructure for the pur- pose of renewables integration have been identi- fied based on Competitive Renewable Energy Zones (CREZ) • EWIS: European-wide transmission study that identifies interim solutions to accommodate the increase in renewables until major transmission 17. This refers to the amount of online generation. For example, in Ire- land, Bömer and others (2010) recommended that a maximum limit of assets are built (which normally take up to 10-15 60 to 80 percent of “inertia-less” power (inverter-connected generation years to build) such as wind and solar PV) should be implemented to maintain suf- ficient system inertia. Appendix B. Summary of International Experience 43 Figure B2. Modeling Tools for Different Studies Positive Sequence Load Flow Simulations Long-term Dynamic Simulations e.g., DigSILENT PowerFactory e.g., DigSILENT PowerFactory 1 sec 1 min 10 min 1 hr 1 day +1 week Voltage support Balancing Inertia Generation adequacy Governor Electromechanical response AGC LVRT impact regulation Economic Operating reserves dispatch Planning Statistical Wind/Solar Power Variability Assessment Dispatch simulation tool Production optimization tool e.g., MATLAB e.g., Multi-Area Production Simulation (GE MAPS) Source: Adapted from [31] slide 10. Generation Adequacy VRE could cause oversizing of the required reserves which Assess dependable capacity (capacity credit) or Effective is economically inefficient.18 Load Carrying Capacity (ELCC) impact on reliability standards. IMPORTANT FOR: The long-term reliability of the power system, that is, its • Systems with high VRE penetration ability to meet demand, can be compromised if the capac- ity contribution of VRE power is assessed inadequately in STUDIED IN: generation planning. Because VRE sources such as wind • IEA Task 25: Summary of methodologies used and solar irradiance are intermittent and difficult to predict, to assess VRE impact on generation adequacy the quantity of energy that can be relied upon to be pro- based on review of prominent VRE integration duced when needed is much lower than in conventional studies power plants. The uncertainty in production availability • Xcel Colorado40: Full reliability calculation based can be reduced somewhat by aggregating VRE sources on +10 years of data across a wide geographic area, and by improving forecast • Germany: ELCC estimated based on duration accuracy. The dependable capacity contribution from curves VRE resources must be assessed as accurately as possible, • NYISO: Approximate method used based on particularly when high amounts of VRE are expected to assessment of VRE contribution during peak replace retiring conventional power plants, so that supply demand periods security can be maintained at the required reliability level. Furthermore, underestimating the capacity contribution of 18. http://www.nrel.gov/wind/systemsintegration/pdfs/colorado_public_ service_windintegstudy.pdf. 44 Appendixes Grid adequacy B.3. Assumptions and Model Importance of a robust transmission design and proactive Requirements grid planning Several methodologies can be used to study each of the Active and reactive power injected by new generation issues described in section B.2. The methodology to adopt can change power flow characteristics and violate ther- depends largely on the amount of data and resources that mal or voltage limits. This is not unique to VRE power, are available, as well as on the objective of the investiga- however. When VRE resources are located farther from tion. Common methodologies and models for each study demand centers, as in the United States and Australia, it is are summarized in table B2. The models used in the stud- more likely that the addition of VRE generation will result ies—the transmission model as well as the generator and in congestion and cause voltage issues, particularly if large other component models—must be validated models. amounts of power are injected at the end of a long feeder The use of models that have not been validated may lead in a radial fashion. to inaccurate simulation results, potentially causing security problems. Figure B2 indicates the types of computer programs that could be used for analyzing each of the elements described. Table B2. Common Methodologies and Models for Various Studies on Impact of VRE Integration Data requirements Element to be Assessed Method Demand Wind Power Generation Nonwind generation Generation Assess whether the a) Historical demand a) High/medium/low a) Available generation Adequacy system can meet reliability (10+ years) wind development capacity considering standards with the addition Hourly or quarter- scenarios (different scheduled and forced of the estimated amount hourly historical distribution of wind outages. In areas with of VRE. To include VRE demand profiles power plants may be high hydro power in the calculation process, b) Defined high demand considered) penetration, reliable use either capacity credit, period based on Hourly or quarter- and firm energy or Effective Load Carrying analysis of historical hourly historical wind availability of hydro Capacity (ELCC). demand power generation resources must be The capacity credit or (may be developed taken into account. ELCC of VRE power can from wind speed b) Not considered be estimated by either the measurements, time- reliability method or the synchronized with approximate method. demand) Reliability method: b) Wind power Calculate reliability metrics generation such as Loss of Load corresponding to high Expectation (LOLE), demand periods Loss of Load Probability (LOLP), and so forth, and compare reference case with VRE power integration case. Approximate method: Calculate average capacity factor corresponding to high demand periods. Note: The Reliability Method is preferred. (continued) Appendix B. Summary of International Experience 45 Table B2. Common Methodologies and Models for Various Studies on Impact of VRE Integration (continued) Data requirements Element to be Assessed Method Demand Wind Power Generation Nonwind generation Grid Planning a) Steady-state power a) Peak and off-peak Aggregated P&Q output of a) P&Q output model flow simulations demand wind power plant based on with full availability for (N) and (N−1) b) Forecast demand fixed wind speed: corresponding to the situations. (historical demand a) For high and low wind point in time analyzed, b) Time-synchronized scaled to future) power outputs and external reactive dispatch (market) power devices b) Corresponding to the simulation (analyses point in time analyzed b) Available generation of inter-area flows and capacity considering often compromised scheduled and forced grid model). outages Electromechanical a) Transient: Dynamic a) Peak and off-peak a) High wind power a) Dynamic models of stability power flow simulations demand output for aggregated generators, external following a 3-phase b) Appropriate static and WPP model, P&Q reactive power devices, fault or sudden loss of a dynamic load modeling output based on and protection generating unit fixed wind speed. equipment c) Appropriate static and b) Small-signal: Modal Model must include b) Dynamic models dynamic load modeling analysis by eigenvalue corresponding low- of synchronous calculation of small- voltage ride-through generators including signal stability with and and reactive power excitation, speed without wind power support capability of governors, and power WPP. system stabilizers. c) Subsynchronous: Electromagnetic time b) Dynamic WPP models External equipment for domain simulations with voltage control oscillation damping. to evaluate the mechanism, or assume c) Electromagnetic time subsynchronous constant mechanical model or HVDC link control interaction torque. or series-compensated between the wind c) Electromagnetic system and external turbine converter and time models of wind devices providing the HVDC link or turbine generators. An reactive power support. series-compensated aggregated model can system be used. Fault level Steady-state short Off-peak demand Aggregated P&Q output P&Q output model circuit calculations based on fixed wind speed. with full availability (Electromagnetic transient corresponding to the point simulations are performed in time analyzed, including for detailed connection external reactive power studies) devices. Inertia and Dynamic frequency Off-peak demand P&Q output based on fixed Dynamic models of frequency response simulations following the wind speed (high output generators, excitation, and sudden loss of generation level) speed governors Wind power plant features such as low voltage ride-through, reactive power support, and virtual inertia may be considered if expected to be implemented. (continued) Table B2. Common Methodologies and Models for Various Studies on Impact of VRE Integration (continued) Data requirements Element to be Assessed Method Demand Wind Power Generation Nonwind generation Balancing Statistical method: a) Historical demand on a a) Per minute wind power a) Not considered (regulation, Estimation of regulation minute basis (> 1 year) generation (time- b) Available generation dispatch, and short- reserve requirements based scaled to future level synchronized with capacity considering term capacity) on the standard deviation of b) Historical demand on demand) based on scheduled and forced net load variability 5–30 minute basis (> historical wind speed outages. Conventional Dispatch simulation: 1 year) scaled to future measurements reserve availability Estimation of tertiary level b) 5–30 minute wind characteristics (ramp reserve requirements power generation and rates, unit start-up and by time-synchronized output forecast values shut-down times, and simulation of the dispatch (time-synchronized so forth) process with demand) based The performance can also on historical wind be evaluated according to speed measurements the resulting carbon dioxide emissions, utilization rate of major interconnectors (if modeled), and curtailed amount of wind energy. Voltage stability Steady-state PV and QV Various load levels, Model the behavior of Various generation and limits analysis representative data on the WPP at the point of dispatch scenarios. voltage dependency connection considered. P&Q model with full (For example in the case of availability corresponding New Zealand, WTGs must to the point in time meet certain requirements analyzed, including external with respect to minimum reactive power devices. power factor, therefore WTGs were modeled as P&Q loads with unity power factor) Note: P&Q = active and reactive power; PV = photovoltaic; WPP = wind power plant; WTG = wind turbine generator. Appendix C. VRE Potential and Wind Contracts in the Philippines Map of Interconnected Regions of the Philippines, Marked with Location of Demand Centers Figure C1.  and Potential for Wind Power Development LUZON Legend Wind electric potential: Very high (3,000–5,200 MW) High (2,000–3,000 MW) VISAYAS Demand centres 440 MW (HVDC) Regions Interconnections Philippines 40 MW 400 MW 100 MW 200 MW 100 MW 200 MW MINDANAO Source: Modified from [32] Page 69 and [5] page 101. 47 48 Appendixes Map of Interconnected Regions of the Philippines, Marked with Location of Figure C2.  Demand Centers and Potential for Solar Power Development LUZON Legend Solar Power Potential–Annual: 5.0–5.5 kWh/m2/day 4.5–5.0 kWh/m2/day VISAYAS Demand centres 440 MW (HVDC) Regions Interconnections 40 MW 400 MW 100 MW 200 MW 100 MW 200 MW MINDANAO Source: Modified from [32] Page 69 and [6] page 9. Appendix C. VRE Potential and Wind Contracts in the Philippines 49 Figure C3. Map of Ocean Power Development LUZON Legend Ocean Power Projects Demand centres Regions VISAYAS Interconnections Philippines 440 MW (HVDC) 40 MW 400 MW 100 MW 200 MW 100 MW 200 MW MINDANAO Source: [9] page 118. 50 Appendixes Table C1. Wind Contracts in the Philippines Projected Capacity Investment Cost Grid/Region/Company Name/Location (MW) (Php) LUZON GRID 748 332,226,378 Region I 326 136,797,510 Alternergy Philippine Holdings Corporation 0 14,100,000 Sta. Praxedes, Cagayan & Pagudpud Wind Power Project 0 14,100,000 Energy Development Corporation 126 92,500,000 Balaoi-Pagudpud Wind Power Project 40 7,000,000 Burgos Wind Power Project 86 85,500,000 Energy Logics Philippines, Inc. 120 28,200,000 Pasuquin-Burgos Wind Power Project 120 28,200,000 Northern Luzon UPC Asia Corporation 30 974,215 Balaoi-Pagudpud Wind Power Project 30 974,215 Northern Luzon UPC Asia Corporation 50 1,023,295 Caparispisan-Pagudpud Wind Power Project 50 1,023,295 Region II 190 89,458,488 Alternergy Philippine Holdings Corporation 0 28,200,000 Aparri Wind Power Project 0 14,100,000 Sta. Ana Wind Power Project 0 14,100,000 FirstMaxpower International Corporation 45 21,075,000 Claveria Wind Power Project 15 7,025,000 Gonzaga Wind Power Project 15 7,025,000 Sanchez Mira Wind Power Project 15 7,025,000 NorthPoint Wind Power Development Corporation 40 8,282,898 Aparri-Buguey Wind Power Project 40 8,282,898 Trans-Asia Renewable Energy Corporation 105 31,900,590 Abulug-Ballesteros-Aparri Wind Power Project 45 10,696,305 Aparri-Camalaniugan-Buguey Wind Power Project 48 11,010,180 Sta. Ana Wind Power Project 12 10,194,105 Region III 30 19,740,000 PetroEnergy Resources Corporation 30 19,740,000 Sual Wind Power Project 30 19,740,000 Region IV-A 111 44,667,840 Alternergy Philippine Holdings Corporation 40 28,200,000 Lumban-Kalayaan Wind Power Project 0 14,100,000 Tanay-Pililla Wind Power Project 40 14,100,000 Trans-Asia Renewable Energy Corporation 71 16,467,840 Bauan-San Luis Wind Power Project 9 2,710,620 Calatagan Wind Power Project 10 2,710,620 (continued) Appendix C. VRE Potential and Wind Contracts in the Philippines 51 Table C1. Continued Projected Capacity Investment Cost Grid/Region/Company Name/Location (MW) (Php) Calauag Wind Power Project 10 2,838,195 Calauag-Lopez Wind Power Project 13 2,693,610 Infanta Wind Power Project 10 2,753,145 Silang Wind Power Project 19 2,761,650 Region IV-B 40 21,100,000 Alternergy Philippine Holdings Corporation 40 14,100,000 Abra de Ilog Wind Power Project 40 14,100,000 Energy Development Corporation 0 7,000,000 Taytay Wind Power Project 0 7,000,000 Region V 36 13,197,540 Trans-Asia Renewable Energy Corporation 36 13,197,540 Mercedes Wind Power Project 10 10,231,770 Paracale-Vinzons Wind Power Project 26 2,965,770 Region VI 15 7,265,000 First Maxpower International Corporation 15 7,265,000 Pulupandan Wind Power Project 15 7,265,000 VISAYAS GRID 173 97,660,520 Region VI 21 7,057,170 Constellation Energy Corporation 0 1,755,000 Ilog Wind Power Project 0 1,755,000 Trans-Asia Renewable Energy Corporation 21 5,302,170 Dumangas Wind Power Project 12 2,625,570 San Joaquin Wind Power Project 9 2,676,600 Region VII 152 90,603,350 Constellation Energy Corporation 0 1,755,000 Bayawan-Tanjay-Pamplona Wind Power Project 0 1,755,000 PetroEnergy Resources Corporation 30 19,740,000 Nabas Wind Power Project 30 19,740,000 Trans-Asia Renewable Energy Corporation 122 69,108,350 Anda-Guindulman Wind Power Project 10 2,710,620 Barotac Nuevo Wind Power Project 12 10,307,100 Ibajay Wind Power Project 10 10,219,215 Malay Wind Power Project 10 10,269,435 Nueva Valencia Wind Power Project 10 10,307,100 San Lorenzo Wind Power Project 54 15,038,000 Sibunag Wind Power Project 16 10,256,880 MINDANAO GRID 0 21,000,000 (continued) 52 Appendixes Table C1. Continued Projected Capacity Investment Cost Grid/Region/Company Name/Location (MW) (Php) Region X 0 7,000,000 Energy Development Corporation 0 7,000,000 Camiguin Wind Power Project 0 7,000,000 Region XIII 0 14,000,000 Energy Development Corporation 0 14,000,000 Dinagat Wind Power Project 0 7,000,000 Siargao Wind Power Project 0 7,000,000 Grand Total 921 450,886,898 LUZON GRID 0.006 0 Region IV-A 0.006 0 DOST- Industrial Technology Development Institute 0.006 0 DOST-ITDI Wind Project 0.006 0 Grand Total 0.006 0 Solar Contract LUZON GRID 1 750,000 Region III 1 750,000 Aurora Special Economic Zone Authority 1 750,000 Casiguran Solar Power Project 1 750,000 Grand Total 1 750,000 Source: DoE 2010. References Alonso-Llorente, J. F. 2005. Integration of Wind Generation within the Energy Regulatory Commission. 2001. “Philippine Grid Code.” Energy Power System: Experiences from Spain. Berlin: Red Electrica España. 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