Wind System Reliability and Capacity

Capacity measures a system’s ability to survive stress. For example, structures are engineered in part to have the capacity to survive the worst wind loads expected over the life of the structure. Likewise wind electric power systems should have the capacity to reliably survive the worst combination of high load and low wind. A superior approach for quantifying wind’s contribution to system capacity is well known. It is to view wind as a negative load and use the Effective Load Carrying Capacity (ELCC) methodology for a given year. A frequent mistake is to average these annual ELCC estimates. A main contribution of this paper is to explain why the system design criteria should take the worst of the annual ELCC estimates over a number of years and not an average of annual ELCC estimates. Based on extreme events, wind generation contributes little to system capacity (<6.6% of wind nameplate). The empirical evidence shows that wind generation is an energy source, not a capacity resource.