September 2007

The final report of the APS Wind Integration Cost Impact Study was produced by Northern Arizona University (NAU), with contributions from EnerNex Corporation, 3TIER, and Arizona Public Service Company (APS).  The report is a result of an eight month study to characterize the impacts and costs due to the variability and uncertainty of wind energy associated with integrating wind energy into APS’ utility resources and practices.

To download Full Report including Executive Summary click here:  APS Wind Integration Study Full report

To download Executive Summary only click here: APS Wind Integration Executive Summary

Overview of Project

Wind energy brings many positive benefits to the utility system, such as cost effective energy, long-term price stability, and some system capacity, but it also has different generation characteristics than conventional utility resources.  In particular, since the wind is driven by meteorological processes it is inherently variable.  This variability occurs on all time frames of utility operation from real-time minute-to-minute fluctuations through yearly variation affecting long-term planning. Recent wind integration studies have demonstrated that the variations of most importance and cost are those in the hourly and daily timeframe, related to the ancillary services of load following and unit commitment. Regulation costs, incurred by fast responding units that respond to the random minute-to-minute fluctuations on the system, are also incurred but are smaller in magnitude. In addition to being variable, wind power production is also a challenge to accurately predict on the time scales of interest to utility planners and operators: day ahead and for long-term planning of system adequacy (i.e., meeting the system peak load during the year).  Wind energy is more predictable in the hour-ahead time frame, but even then the uncertainty in wind forecasts must be accounted for in utility operation and dispatching. In order to minimize impacts and maximize benefits, each utility that incorporates wind energy must learn how to accommodate the uncertainty and variability of wind energy in their operational and planning practices, and do so while maintaining system reliability.

The objectives of this study were to analyze operating impacts and costs of integrating various levels of wind energy in the APS balancing area (i.e., control area), due to the variability and uncertainty of wind energy. Specifically, attention was focused on the amount of wind energy the APS system may see in the relatively near term, and therefore would provide a fair integration cost to utilize in evaluating wind energy proposals in APS’s current and future RFP’s. 

The results obtained in any integration study are highly dependent on the input assumptions and analysis methods. The philosophy adopted by APS in this study was to determine a realistic, yet conservative, value for the integration cost (i.e., within the limitations of the modeling, come as close as possible to the actual integration cost without underestimating).  Furthermore, the study process was devised to produce meaningful, broadly supported results through a technically rigorous, inclusive study process. Northern Arizona University was the lead organization in the study effort, working in collaboration with APS, EnerNex Corporation, and 3TIER. NAU was responsible for managing the project and for overall technical direction. EnerNex was the primary technical consultant on the integration analysis, 3TIER was responsible for the wind speed and power modeling, and APS was responsible for system characterization and modeling. A Technical Advisory Group was formed to provide external review and guidance to the study), and in particular were counted upon to assist in selecting key model assumptions and parameters used in the study.  A stakeholder group was also formed, from which the project team sought interaction and input regarding all aspects of the project, including wind resources, technical details, and policy ramifications. The organizations invited to the stakeholder meetings were also expected to serve as conduits of information to the people and organizations they represented. With reference to the  Executive Summary and the full report, the links to which are provided on this web page, the integration costs determined in this project are similar in magnitude to others that have been reported for other utilities in the USA.