Wind Power Forecasting Methodology Issues

1. Texas NodalEnergy Management System Alternate Wind Power Forecasting MethodologyFebruary 5, 2007Jay DondetiEMS Project Engineer http://nodal.ercot.com 1

2. Wind Power Forecasting Methodology Issues • Vendor currently plans to forecast the total ERCOT System 80% Probability of Exceedance (POE) forecast value, instead of aggregating the individual WGR 80% POE forecast values. • Potential Issue: The aggregated value of the individual WGR 80% POE forecast values will always be lower than the total ERCOT System 80% POE forecast value because the distribution errors associated with the individual wind plants are not perfectly correlated and so some errors may cancel each other out • Potential Solution: Develop a method that calculates a forecasted hourly power output value for each individual WGR such that the sum of these values equals to the 80% POE forecast value for the total ERCOT System http://nodal.ercot.com 2

3. Proposed Wind Power Forecasting Methodology • Option 1: • Calculate the total ERCOT System forecast 80% POE value and associated error distribution • Calculate the individual WGR 80% POE values and associated error distribution • Disaggregate the total ERCOT System forecast 80% POE value, in proportion to individual WGR 80% POE values to compute hourly production output for WGRs • Use these value for RUC through QSE updated COP. • This method does NOT account for the degree of correlation in forecast errors among the individual WGRs, and between the individual WGRs, and the total ERCOT System. • Option 2: • Calculate the hourly production output for WGRs as described above • Apply a correction factor derived from each WGR forecast error correlation to the ERCOT System forecast error • Vendor is still investigating the implementation details of this method http://nodal.ercot.com 3

4. Questions & Answers http://nodal.ercot.com 4