1 Capacity Forecast Report Mark Ruane Director, Market Credit CWG / MCWG March 10, 2015 ERCOT Public

2 Capacity Forecast Model ERCOT Public ERCOT began posting of the capacity forecast model results commencing February 24 th for Operating Day February 23 rd. The report shows: Hourly forecast MW excess reserves for OD+1 through OD+6, with partial day forecast for OD+7. For OD-1 through OD-7, Hourly MW forecast for the Operating Day generated on the OD-1 relative to that day (eg the most recent capacity forecast for that day) Actual MW excess reserves for that hour HUBBUSAVG price for the hour Forecast values are P50. ERCOT may consider possible P x forecast values.

3 Capacity Forecast Model ERCOT Public For the ODs for which results are available, the OD+1 forecast more often than not underestimated reserves on the OD (consistent with initial concept modelling). False positive False negative

4 Capacity Forecast Model ERCOT Public Percentage error False positive False negative

5 Capacity Forecast Model ERCOT Public There are five ODs for which there are both OD+4 and actuals. For each of the days the OD+4 forecast was higher than actual. Lesser error Greater error

6 Capacity Forecast Model ERCOT Public For the five days with both OD+1 and OD+4 forecasts there was generally a material reduction in forecast error. Reduced error Increased error

7 ERCOT Public Questions Capacity Forecast Model