Guest Editorial

GUEST EDITORIAL

What Does 20% Look Like?

Developments in wind technology and systems


	J. Charles Smith and Brian Parsons

Photo courtesy of PPM Energy

What does 20% of what look like? Before we answer that question, let me say that it is a great pleasure for me and Brian Parsons to serve as the guest editors for another special issue of IEEE Power & Energy Magazine dedicated to wind technology and utility systems. Since the first thematic issue on this topic in November-December of 2005, the wind industry has continued to exhibit substantial growth both domestically and internationally. There are now over 75,000 MW of wind capacity installed worldwide, and over 12,000 MW in the United States. There have been some significant developments in the technology and in our understanding of how to integrate large amounts of wind into the grid, and some significant developments on the policy front, since the last issue. We have once again been able to assemble a strong team of international contributors to coauthor a very timely and highly informative series of articles on the global state of wind power from a power systems perspective.

Context and Drivers for Global Interest in 20%

One of the dramatic developments on the policy front in the United States is the growing concern with global climate change and the growing chorus of voices pushing for some action on the renewable energy and energy efficiency fronts to deal with the possible consequences. A number of different policy drivers are being discussed in the U.S. Congress and state capitols. Among these are the Production Tax Credit (PTC), a Renewable Portfolio Standard (RPS), a carbon cap and trade system, and a carbon tax. It is too soon to tell what policies will be adopted, or when, but the current thinking is that some new renewable energy policies will be adopted sometime in the next few years.

The PTC has been passed for periods of typically two years previously, and the short duration has led to the lack of a consistent, long-term policy environment necessary to encourage wind plant investment. The PTC is currently enjoying a three-year run to the end of 2008, due to a one-year extension being added at the end of 2006 before the last two-year extension expired at the end of 2007. There are bills being discussed in Congress to extend the PTC for periods of two to five years, but nothing is definite at this time. The PTC has been the main policy instrument used in the United States to encourage wind power development.

In the last few years, the RPS has been getting a lot of attention at the state level. The states provide a policy laboratory of sorts, where different approaches to ideas can be tried before Washington policy makers have to make decisions on national legislation. Nearly half of the states have implemented an RPS requiring some level of renewable energy to be phased in within a certain period of time. There is a growing concern that 50 different RPS requirements may not be in the best interest of the country, leading to greater visibility of the issue in Washington. In many states, wind energy would be the primary source of energy used to meet the requirement. There is a growing realization that without a strong commitment to build the necessary transmission, the RPS goals will not be met. One of the most aggressive state RPS requirements in the country is that of California, which requires that 33% of its electricity come from renewable energy by 2020. California is now becoming proactive in dealing with the transmission implications of that requirement. A map illustrating the current states with an RPS is shown in Figure 1.

A significant amount of activity is underway at both the state and national levels to explore carbon cap-and-trade systems, and a carbon tax. The cap-and-trade system appears to have more support than the carbon tax at the present time due to it being a market-based approach. Six states have already entered into a cap-and-trade agreement for carbon. A number of leaders in the utility industry, including the Edison Electric Institute (EEI), have come out in favor of such a system in order to provide some investment certainty for the future. This is a critical matter in light of the need to make multibillion dollar decisions regarding the next round of generating plant investment. Numerous bills have been introduced into this session of the Congress, but like the PTC, it is too early to tell what their final disposition will be.

Europe adopted policies in support of renewable energy development long before the United States. The countries with the most installed wind capacity are Germany, Spain, and Denmark. Each of these countries initially adopted some sort of feed-in tariff, which established a mandatory purchase price for wind energy for a fixed period of time. This provided a stable long-term policy environment with investment certainty and encouraged significant investment in wind plants. At the end of 2006, Europe had approximately 50,000 MW of wind capacity installed of the 75,000 MW worldwide.

Looked at in terms of energy penetration levels, i.e., the ratio of the wind energy delivered divided by the total energy delivered, Denmark has reached the highest levels, above 20% for Jutland, the western half of Denmark synchronously interconnected to the south with Union for the Coordination of the Transmission of Electricity (UCTE), and connected to NORDEL to the north by dc. In some hours of the year, the wind energy penetration exceeds 100%, with the excess sold in the balancing markets to NordPool and Germany. The penetration level in Germany has reached 8%, while Spain has reached about 6%. In addition, Europe has recently stated its intention in European Union legislation to provide 20% of its total energy requirement from renewables by 2020, with the details to be worked out in individual countries. By comparison, the level in the United States today is less than 1%.

During the past year, the American Wind Energy Association (AWEA) and the Department of Energy/National Renewable Energy Laboratory (DOE/NREL) undertook an investigation to see what 20% of electrical energy from wind, nationwide, would "look like" in 2030. This effort will be referred to as the Vision Scenario in the following discussion. The investigation covers all aspects, including wind resource assessment, material and manufacturing resources, environmental and siting issues, transmission and system integration, and public policy. Comparable levels of wind penetration have been included in some state RPSs. In addition, a number of utility wind integration studies are being carried out at these levels. Two that have just concluded are the State of Minnesota, which looked at 15, 20, and 25% by 2020, and the State of California, which looked at a 33% RPS in 2020. These studies are further discussed in the article by DeMeo et al.

Based on a high-level linear programming national G&T expansion planning model (WinDS) developed by NREL, a cost/benefit assessment of the Vision Scenario was conducted. The results of the analysis will be released in a report from AWEA/DOE in the second half of 2007. So what does 20% look like? Brian Parsons and I participated in the study, and we will provide a preliminary look at some of the results here. An initial look at the location of the wind generation, by state, to provide this level of energy, about 300 GW of capacity, is provided in Figure 2.

Transmission for the Vision Scenario

A look at the new transmission corridors that would be needed to provide the transmission infrastructure to move this energy from the resource areas to the load in the Vision Scenario was investigated in a conceptual planning effort performed by AEP, one of the world's leaders in high-voltage transmission development and operation. AEP produced a white paper that included a 765-kV network overlay for the U.S. power system that would increase reliability, reduce costly congestion, and allow for up to 400 GW of wind or other new generation to be integrated into the U.S. electrical system. The intent of the effort was to provide a creative impetus to the larger discussion that must take place in order to modernize and expand the nation's transmission infrastructure to realize the future vision. The conceptual plan is illustrated in Figure 3. A 765-kV overlay is extended across much of the country in order to move the large amounts of wind from the often remote resource centers to the load centers in as cost-effective a fashion as possible. This plan provides for 19,000 mi of new 765-kV line at a cost of approximately US$60 billion. While conceptual in nature, and not the result of a detailed system analysis, it is consistent with the results of the WinDS transmission analysis performed by NREL, and it does illustrate the magnitude of the effort required to extend an interstate highway system for electricity across the country and create the infrastructure necessary to enable robust, well-functioning markets to operate.

Resources and Manufacturing for the Vision Scenario

There are serious questions about the materials and manufacturing resources necessary to reach a sustainable 20% wind energy penetration scenario and the magnitude of the effort required to scale up the manufacturing and materials supply industries to meet the challenge. An independent study was undertaken by NREL and GE to examine this question. The study looked at the feasibility of reaching 20% wind energy by 2030, and sustaining that level thereafter, assuming continued growth in electricity demand, and re-powering of existing installations. Figure 4 shows the annual and cumulative wind capacity installations prescribed in modeling the costs, benefits, and other impacts of the Vision Scenario. Annual capacity increases are limited to 20%. These growth rates are aggressive but can be achieved by heavy manufacturing industries. It was assumed that a stable policy environment that would support the necessary investment was in place. As a point of reference, the total world wind turbine manufacturing output in 2006 was approximately 15,000 MW, the level necessary to satisfy the requirements of the U.S. alone in the out-years of this scenario.

For large-scale manufacturing, the availability of raw materials such as steel, fiberglass, resins for composite and adhesive, and permanent magnets and copper is critical. Although the availability of these materials is not currently restricted, a major increase in production could be challenging for fiberglass, resins, and core. In addition to raw material supply, the availability of manufacturers and suppliers of components could similarly present a challenge. There is currently a shortage of gearbox suppliers; a significant increase in investment in this component would be required. Although the availability of steel itself will not pose a materials challenge, the size and availability of large steel castings, such as those for rotor hubs, will also present a manufacturing challenge due to the limited number of suppliers of these large, precision-machined parts.

Intermittent Wind Farms

As we think and talk about wind power and power systems, I would like to encourage some thought be given to the vocabulary we use to describe what we are talking about. I am thinking particularly of two words often used to describe different aspects of wind power, one being wind farms and the other intermittent. While there is nothing wrong with the term wind farm, it does conjure up in my mind a picture from days gone by. It is a picture from the early days of the industry, when small wind turbines were being installed in small groups on the subtransmission and distribution system, and no one, not even the utilities to whom they were connecting, thought they would ever amount to much of anything. They were sometimes a curiosity, sometimes a nuisance, not to be taken too seriously, something to be removed from the system during a disturbance and brought back on after the disturbance had passed.

Those days are gone. Wind plants are now as large as or larger than many conventional power plants. Last year, Florida Power and Light Energy (FPLE) dedicated the largest wind plant in the world, the 735-MW Horse Hollow wind plant in Texas. Utilities now require the same sort of terminal behavior from a wind plant as that of a conventional plant, in terms of the ability to ride through a voltage excursion and remain connected to the system and to provide reactive power support to the system immediately after a fault. We can no longer tolerate the removal of the wind plants from the system during a major disturbance. We have made a transition from a wind farm to a wind power plant, and our vocabulary is now beginning to reflect that.

The other term we need to examine is intermittent. I often hear wind referred to as an intermittent resource. This is another term out of the distant past. To most people, the term intermittent means a random sort of unpredictable on-off behavior. This term is usually used in a negative sense. The understanding conveyed is that the output of the plant cannot be predicted and that it rapidly goes from no-load to full-load conditions, or vice versa. While this view was prevalent after looking at the output of a single wind turbine, before we had sufficient data to understand the behavior of large, modern wind plants, it is no longer the case. We now know that the output of wind plants varies very little in the time frame of seconds, more in the time frame of minutes, and most in the time frame of hours. The typical standard deviations of the step changes at the one-second, ten-minute, and one-hour time frames vary from approximately 0.1% to 3% to 10% of rated capacity, which is far from intermittent. A good wind plant output forecast can also predict the changes that will occur with a good degree of accuracy most of the time. As a result of this improved understanding of the behavior of wind plants, we are making a transition away from the term intermittent to variable output, which describes much more accurately the nature of the quantity with which we are dealing.

The Articles

The first article, by Robert Thresher (NREL) et al., provides a look at the wind resource, the history, and the technology behind the modern wind turbine and the R&D opportunities available to continue to increase the capacity factor and reduce the overall cost of wind energy. Robert is the head of the DOE/NREL National Wind Technology Center in Golden, Colorado, where he manages the overall national wind research program. His article provides a fascinating glimpse into the engineering effort that has gone into getting the technology where it is today. It also looks at the R&D effort necessary to support the continued development of the technology, including the long-term needs of the offshore wind technology development program.

The second article, by Robert Zavadil (EnerNex Corp.) et al., provides a report on the status of the industry regarding the task of interconnecting this new form of generation into the power system. One of the areas of great interest to power system engineers is the dynamic models necessary to carry out short circuit and system stability studies with this new form of generation, particularly when the machine architecture includes a power electronic interface. Much has been accomplished in this area in the past two years, including an order from the Federal Energy Regulatory Commission (FERC) detailing the basic interconnection requirements for new wind power plants. This article will explore the collector system design within the wind plant as well as the connection to the external world, which represents an addition to the topics that were covered in the previous issue.

The third article, by Edgar DeMeo (Renewable Energy Consulting Services, Inc.) et al., provides a nice update on the status of utility wind integration studies going on around the country. Since the last topical P&E issue on wind integration, advances have been made in both study methodology and wind penetration levels studied. A broader range of utilities is involved in the studies, and the range of systems explored has been expanded to include those with high levels of hydro capacity. The study of the 33% RPS in California by 2020 is particularly interesting, being the highest level of renewables penetration yet studied in the United States. The Minnesota study is quite interesting for the insights it provides into the benefits of well-functioning markets operating across broad geographical regions, as is the Avista work for the insights gained through parametric investigations.

As higher levels of wind penetration are being studied around the country, it is becoming increasingly clear that a robust transmission system will be necessary to interconnect these often remote resources to the transmission grid and deliver the energy to load. Some novel approaches to transmission expansion are being investigated to break the logjam in the development cycle between wind development and transmission availability. There is a growing recognition of the importance of market design in the ability to incorporate large amounts of variable output renewables into the generation mix. Recent actions on the part of FERC to update the Order 888 Open Access Transmission Tariff with the new Order 890 have taken place. All of these trends will be more fully explored in the article by Richard Piwko (GE) et al. on developments in transmission and markets affecting wind energy.

No series of articles on the role of wind plants in power systems would be complete without a discussion of what's happening with wind forecasting. The article by Bernhard Ernst (RWE Transportnetz) et al. brings out the most recent experience with wind forecasting from Europe and the United States. Recent insights on the increased levels of accuracy in both the hour-ahead and the day-ahead time frames are provided. The importance of the size of the area for which the forecast is being provided on both the forecast accuracy and the reductions in wind plant variability is remarkable. Some very exciting developments in the use of ensemble techniques to continue to improve the accuracy of wind plant output forecasts in the future are described. Progress being made in integrating the forecasts into the utility operations planning and real-time operations time frame is also discussed.

In the last article, Thomas Ackermann (Royal Institute of Technology in Sweden, KTH) et al. take a look at some of the challenges that are being met with the increasing penetration of wind power on the European power systems. The European Commission has recently announced a goal of providing 20% of Europe's total energy from renewables. That goal is being translated into individual national goals, and it appears that wind will continue to play an ever increasing role. As higher wind penetrations have been achieved earlier in Europe than the United States, the European power systems already have experience in developing new technical and market approaches to deal with the system balancing issues. The development of wind power in Europe is shifting off-shore due to the population density distribution on land. The development of technology to deal with off-shore networks and higher levels of penetration are also explored in this article through the experience with one of the pioneering Danish off-shore installations at Horns Rev.

Creating Wind Power Plants

A great challenge that lies before us is creating the wind power plants of the future. In order to be looked upon as a truly integral part of the system of the future, and not as an inferior form of generation, wind power plants will need to look and act more like conventional plants from a terminal point of view. We know that the output cannot be fully scheduled over long periods of time. But it can be scheduled over short periods of time with a known degree of accuracy. Wind power plants can be integrated into an automatic generation control system. Wind power plants can participate in the provision of ancillary services, such as providing spinning reserves in both the up and down direction. With today's technology, it is a matter of economics, not a matter of ability. Wind power plants can participate in frequency regulation and can provide an inertial response if desired. These features are available with the advent of new power electronic controlled interfaces. These same controls allow the ability to provide voltage control and reactive power control as well. The days of the uncontrolled simple induction machine interface are long gone. Controllable wind power plants are the way of the future. Wind plant voltage can be controlled to hold system voltage constant at a remote bus, even under widely varying wind speed conditions. Examples of voltage control features provided on recent wind plants in Colorado and Denmark are provided in the articles on interconnection and European experience, respectively.

Summary

Asking the question of what a world with 20% of our electricity coming from wind looks like raises a lot of interesting questions. Do we have enough wind resource, manufacturing capacity, and materials? How much wind energy can the power system accommodate? How much flexibility do we need to build into the rest of the system to accommodate the wind? How much transmission needs to be provided? What changes need to be made to system and market operation practices? What is the role of wind forecasting? How far can we go with wind power plants? How much will it all cost?

I think that these articles help start to provide answers to these questions, or at least help us get pointed in the right direction. All we know for sure is that the future will be different from the past. The needs of the society in which we live are changing, and those needs are placing new demands on the power engineering community. We cannot expect the utility community to be leading the charge for change, given their mandate to operate the system at least cost consistent with a very high degree of reliability. We can expect that the utility system professionals will respond to the needs of society, as they always have, and respond to the laws and policies of the land in the best way that they know how.

Conclusions

There is a great opportunity for today's power engineering profession to lay the groundwork for a bright new future for the next generation of power engineering professionals by responding to the new demands being placed upon them with innovative and creative ideas about how the new goals of society can be met. This is the opportunity of a lifetime. It is not every day that we have the opportunity to be present at the creation of a new industry, and the fundamental shifts that we see taking place as we come to grips with the implications of planning for life in a carbon constrained future.

The challenge is before us. It is up to us to pick up the challenge and meet it head-on. It is my contention that there is no more dedicated and talented group of people than the power engineering professionals and support staff who plan, design, construct, and operate our electric power system. There is a massive amount of investment and inertia in the current system, so the change will come slowly, but it will come, and we need to help shape it. I am confident that this tremendous group of talented and creative people who have dedicated their professional careers to this area will rise to meet the challenge, and I look forward to working with you to help create the future.

Acknowledgment

We would like to acknowledge the guidance, support, and encouragement provided by the Editor-in-Chief Mel Olken, who had the vision to go down this road that many feared to travel. It has been a great pleasure to work with Mel on this issue.