Realizing the benefits of enhanced capabilities of wind turbines will depend in large part on the overall wind plant design, since the actions of a large number of relatively small wind turbines must be coordinated to have positive impacts on the overall power system.
Reactive Power Management and Dispatch
Because of the fast pace at which the wind industry has emerged and grown over the last decade, the reactive power characteristics of a wind plant are more often than not an “outcome” rather than a design requirement. With more stringent interconnection requirements, more attention and analysis will be given to this topic for plants built over even the next few years. The required reactive power capability of a wind plant will be determined from the results of the interconnection study, and will drive the overall wind plant design, possibly impacting even turbine selection. Where the transmission system interconnection is weak or vulnerable, there will be more use of auxiliary equipment such as static var compensators. As design experience accumulates, the ability of the wind plant to provide for the needs of the transmission system at the point of interconnection will be much improved.
Communications and Control
The communications and control infrastructure of even present-day wind plants is quite sophisticated, with high-speed SCADA to each turbine and other critical devices or points within the collector system. This sophisticated infrastructure has yet to be exploited for purposes of improving the interconnection performance and integration of the wind plant with the power system; mostly it has been used for maximizing plant production and availability. In the future, this infrastructure will be the foundation upon which many of the advanced features and capabilities will be based. The interface between the wind plant control center and power system control area operations will also be developed to a much higher degree. Advanced wind plant performance such as AGC participation will likely be accomplished by the control area EMS interacting with the wind plant control center, rather than from EMS to individual wind turbines. Such an interface would also facilitate other plant capabilities that could benefit power system security and reliability, such as automatic full – or partial-curtailment of wind generation under severe system contingencies.
Wind Plant Production Forecasting
While the fast fluctuations in wind plant output can create problems with respect to voltage flicker and reactive power management, somewhat longer term fluctuations in wind plant production appear to be of the most consequence for control area operators. More specifically, the uncertainty over what wind plant production will be during the next hour, or by hour for the next day is the major question. Planning conservatively to cover a possible reduction in wind plant generation results in higher reserve margins and higher cost if not needed. Backing down economic generation to accommodate a sudden increase in wind generation can also increase costs. All of the analytical studies of the impacts of wind generation on power system operations have one theme in common: Better predictions of what wind generation will do at some time in the future allow the control area operators to better plan for the most economic set of resources to meet the remaining load. Much research work is ongoing in the area of wind production forecasting, and at least two commercial services have been launched to assist wind plant operators with sophisticated meteorological and statistical methodologies for improving the accuracy of production forecasts. Wind generation forecasting has already been incorporated into the market rules for the California ISO, in exchange for preferable treatment with respect to settlement of imbalance energy and unscheduled deliveries. Continued focus on wind generation forecasting as a way to mitigate the uncertainty in future wind energy deliveries are expected to improve the science and methods that underlie these systems. Assumptions about the ability to forecast wind generation at some time in the future can make a critical difference in the analysis of wind generation of power system operations and control. On shorter time scales, say for the next hour, the uncertainty about average wind speed will be smaller, so the variations in wind plant production compared with an average or scheduled value have more to do with the variability of the resource over the expanse of the wind plant and the factors discussed previously. As the forecast moves out into the future, the meteorological details take precedence.