Characterizing and mitigating the wind resource-based uncertainty in farm performance

A farm planning strategy that simultaneously accounts for the key engineering design factors and addresses the uncertainties in a wind project can offer a powerful impetus to the development of wind energy. In this context, the resource itself is highly uncertain - wind conditions, including wind speed, wind direction, and air density, showstrong temporal variations; in addition, the distribution of wind conditions varies significantly from year to year. The resulting ill-predictability of the annual distribution of wind conditions introduces significant uncertainties in the estimated resource potential or the predicted performance of the wind farm. In this paper, a new methodology is developed (i) to characterize the uncertainties in the annual distribution of wind conditions, and (ii) to model the propagation of uncertainties into the local wind power density (WPD) and into farm performance evaluation. Key measures of farm performance include annual energy production (AEP), cost of energy (COE), and payback period. Both parametric and nonparametric uncertainty models are formulated, which can be leveraged in conjunction with a wide variety of stochastic wind distribution models. The AEP and the COE are evaluated using advanced analytical models, adopted from the recently developed Unrestricted Wind Farm Layout Optimization (UWFLO) framework. The year-to-year variations in the wind distribution and the quantified uncertainties are illustrated using two case studies: an onshore and an offshore wind site. Appreciable uncertainties are observed in the estimated yearly WPDs over the 10-year period - approximately 11% for the onshore site and 30% for the offshore site. The uncertainty in COE is mitigated for the onshore site using the nonparametric uncertainty model within the UWFLO framework. The ensuing robust optimization process illustrated how important it is to reduce the sensitivity of the farm performance to unreliable wind conditions, even though they may be frequent in certain years and/or contain higher energy density.