The value of operational flexibility in power systems with significant wind power generation

There is a growing body of evidence demonstrating how large penetrations of wind power generation in power systems contribute to increase the cost and the complexity of grid operations. Those costs and increased complexity are directly linked to the random nature of the wind over time, which requires system operators to carry more reserve capacity to cope with that randomness if current security and reliability standards are to be maintained. Moreover, as the frequency spectrum of the wind generation random process is relatively wide (from 10^-6 to about slightly above 1 Hz), the reserves available must be capable to be deployed fast enough to counter this variability. Therefore, in systems with significant wind power penetrations the security-constrained unit commitment programs should be capable of capturing the reserve capacity deployment requirements entailed by the random wind dynamics. More fundamentally, however, what is required is that the dispatchable portion of the generation system providing reserves is flexible enough. In other words, there must be enough flexible capacity available to ramp up and down so to shadow the wind´s caprices. In this paper, we formulate a modification of the classic unit commitment formulation ot assess the value of such operational flexibility in power systems with large proportions of wind capacity. We discuss some economic and technical indicators of flexibility.