NREL Releases Wind Curtailment Case Studies

The report, which was written for NREL by the consulting firm Exeter Associates, compiles available information about the frequency and severity of wind curtailment in various regions of the U.S., as well as in other countries. Based on these case studies, the report concludes that congestion on the transmission grid caused by inadequate transmission capacity is the primary cause of nearly all wind curtailment.

Wind curtailment typically occurs when there is excess electric production in an area and there is insufficient transmission capacity to move that electricity to demand centers. While other kinds of power plants typically reduce their output before wind plants do, given that the fuel costs and other operating costs of those plants are higher than those of a wind plant, in some cases wind plants may also be called on to reduce their output. Almost all wind plants can curtail their output, typically by pitching the blades of the wind turbine out of the wind.

According to the study, wind curtailment has been occurring frequently in regions ranging from Texas to the Midwest to California. Curtailment has also become a problem abroad, with significant curtailment occurring in Spain, Germany, and the Canadian province of Alberta. Wind curtailment may occur as a condition of generator interconnection, per contractual agreements that allow for wind curtailment at low or reduced cost to the wind power purchaser, or through allowing wind generators to bid a price that includes their willingness to be curtailed.

The report also discusses some of the potential solutions for reducing wind energy curtailment. Building additional transmission capacity is presented as the most effective way to address wind curtailment’s primary cause—insufficient transmission capacity on our existing power grid. Several transmission projects have been announced or are in planning that may accommodate thousands of megawatts of new wind projects by the time these transmission projects are in operation between 2013 and 2015. The timely completion of these new power lines is by no means certain, though, and wind curtailment will likely persist, if not worsen, until new transmission is available.

The report also discusses stop-gap measures that can reduce wind curtailment while the obstacles to building new transmission are being resolved. These measures include creating larger grid operating areas, implementing programs to dynamically rate the capacity of transmission lines according to ambient weather conditions instead of worst-case assumptions, and allowing greater dynamic scheduling of power flows between neighboring regions.

To read the study, click here.