necessarily.” While it is natural to think that batteries or other storage systems might be needed to accommodate the variable output of wind plants, they are not necessary at the present time. 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 viewed as a resource for the overall power system to be deployed when it is the most cost effective source of needed flexibility. It would not be cost effective or efficient to couple energy storage resources exclusively to individual wind plants.

Wind Integration’s Cost

To address wind energy’s variability, some incremental generation may be required for system balancing. While this is not a reliability issue, it can add a modest amount to the overall cost of electricity service. The costs of this generation include the costs of keeping the generators available and ready to operate and the fuel costs of operating them. The exact costs depend on the mix of generation on a given system and various other factors. In a condensed five-page summary of these studies by the Utility Wind Integration Group written in 2006 (in coordination with the Edison Electric Institute, the American Public Power Association and the National Rural Electric Cooperative Association), the wind integration studies performed to date were summarized by the following conclusions:

• Wind resources have impacts that can be managed through proper plant interconnection, integration, transmission planning and system and market operations.

• On the cost side, at wind penetrations of up to 20 percent of system peak demand, system operating cost increases caused by wind variability and uncertainty amounted to about 10 percent or less of the wholesale value of the wind energy. These conclusions will need to be reexamined as results of higher-wind-penetration studies—in the range of 25 percent to 30 percent of peak balancing-area load—become available. However, achieving such penetrations is likely to require one or two decades.

•In the next one to two decades, changes are likely to occur in both the makeup and the operating strategies of the nation’s power system. Depending on the evolution of public policies, technological capabilities and utility strategic