 The study presents a probabilistic method to determine net load forecast uncertainty for day-ahead wind and load forecasts, and demonstrates that the required capacity ranges from 2,100 to 5,700 mW for ERCAT and 1,900 to 4,500 megawatts for MISO, depending on the wind and load forecast values. Additionally, the study shows that for each mW of additional wind power capacity for ERCAT, 0.16 to 0.30 megawatts of dispatchable capacity will be used to compensate for wind uncertainty based on day-ahead forecasts, while for MISO, with its more accurate forecasts, the requirement is 0.07 to 0.13 megawatts of dispatchable capacity for each mW of additional wind capacity. This article was authored by Brandon Marche, Jay Apt, Pedro M.S. Carvalho and others.