utilities and wind power

Reliability

Utilities can typically add wind generation to their power supply mix without major adjustments in the planning, operations, or reliability of their systems, according to several recent studies looking at experience or modeling wind integration scenarios, as well as experience in Europe. When wind isn’t blowing, reliable electrical service is maintained by turning up the output of other generators on the electric power system.  Electric utility companies serve as "system operators", which can be thought of as air traffic controllers of the power system.  System operators can control, or dispatch, generators on their system such as natural gas-fired and hydro generators.  They have always actively dispatched their systems in response to electrical demand, or load, which varies randomly over the course of an hour or day.  Wind behaves similar to load in that it is “variable,” meaning its output rises and falls within hourly and daily time periods; and it is “non-dispatchable,” meaning its output can be controlled only to a limited extent.  Reliable electrical service can be maintained by system operators dispatching generators up and down in response to variation in load and wind generation.  System operators also keep generation in reserve, called "operating reserves," which can be called on in case of a shortfall.

According to Paul Bonavia, Chief Operating Officer of Xcel Energy, one of the nation’s largest electric utility companies:

"Wind energy is an integral piece of our power supply portfolio. It provides a hedge against fuel price volatility associated with other forms of electric generation. Our studies and experiences show that wind energy integrates effectively and reliably into our power systems with regional market operations to mitigate the impact of wind variability. In these cases even with 25 percent of the electricity on our system from wind we forecast cost for operating system reserves of approximately $5 per megawatt-hour, or roughly ten percent of the cost of the wind energy. As we gain experience with wind we keep seeking ways to achieve low integration costs."

Is Energy Storage Needed? 
No, while it is natural to think that batteries or other storage systems might be needed to supply steady power, it is not needed to integrate wind energy into electric power systems.  The power system essentially already has storage in the form of hydro reservoirs, gas pipelines, gas storage facilities, and coal piles that can provide energy when needed.  Storing electricity is currently significantly more expensive than using dispatchable generation. In the future, through advances in technologies such as batteries and compressed air, energy storage may become cost-effective.  The prospect of plug-in hybrid electric vehicles holds great promise because the expense of their batteries would be covered by their fuel cost savings and they could provide many megawatts of storage for the overall electrical power system.  This would allow wind power and other renewable energy resources to displace consumption of foreign oil.  Still, energy storage will best be used as a resource for the overall power system.  It would not be cost effective or efficient to couple energy storage resources exclusively to individual wind plants.

Is wind less "reliable" than conventional generation?
No. Conventional resources occasionally shut down with no notice, and these "forced outages" require operating reserves.  For example, a power system that has 1000 Megawatt nuclear or coal plants will typically keep 1000 Megawatts of other generation available, to be ready to quickly supply electricity if a plant unexpectedly shuts down.  The power system can still be operated perfectly reliably in this fashion. Thus, "reliability" is not specific to any single generation facility, rather it is measured on a system-wide basis.

As noted by Jon Brekke, Vice President of Member Services for Great River Energy, a utility that operates in Minnesota and Wisconsin:

"Wind energy is a valuable part of our diverse and growing energy portfolio. When partnered with other traditional generation resources, wind energy is an effective way to provide reliable, clean and affordable power to our member cooperatives. Geographic diversity of wind energy helps even out the variability of wind energy in the regional market. In addition, wind farms are typically made up of many individual turbines which reduce the impact of outages. For instance, there are 67 1.5 -MW turbines at our Trimont Wind Farm, so if one is down for maintenance only 1.5% of the total wind farm's generating capacity is lost."

Changes in wind energy output are not instantaneous, as are conventional generator failures. Because of the geographic diversity inherent with large numbers of wind turbine installations, it typically takes over an hour for even a rapid change in wind speeds to shut down a large amount of wind generation. This is a significant benefit when compared with the instantaneous tripping of conventional units. In addition, wind forecasting tools that warn system operators of pending major wind output variations are becoming widely used and better integrated into system operations.

See the links to the upper left to learn more about specific topics related to electric utilities and wind power. To learn more about AWEA membership, to view U.S. wind power projects by location, or to register for an upcoming AWEA event related to wind power, click on the links to the lower left. Other sources of wind power information from other organization can be found at the upper right. For more information, contact Jeff Anthony, AWEA Manager of Utility Programs at 414-967-5950 or janthony@awea.org.