The wide range of factors contributing to Wind Resource Assessment accuracy in complex terrain

Abstract. Understanding the uncertainties of Wind Resource Assessments (WRA) is key to reducing project risks, and this is particularly challenging in mountainous terrain. In the academic literature, many complex flow sites have been investigated, but they all focus on comparing wind speeds from selected wind directions, and do not focus on the overall AEP. In this work, a range of simulations are carried out with seven different wind modelling tools at five different complex terrain sites and the results compared to wind speed measurements at validation locations. This is then extended to AEP estimations (without wake effects), showing that wind profile prediction accuracy does not translate directly or linearly to AEP accuracy. This is firstly because there is a surprisingly large variation in energy production calculation techniques between tools, and secondly because the AEP depends strongly upon the relative strength and occurrence of the wind speed in the most commonly-occurring wind direction sectors. This means that the wind model that produces the most accurate wind predictions for a certain wind direction over a certain time period does not always result in the most suitable model for the AEP estimation of a given complex terrain site. In fact, the large number of steps within the WRA process often lead to the choice of wind model being less important for the overall WRA accuracy than would suggest by only looking at wind speeds. It is therefore concluded that it is vitally important for researchers to consider overall AEP – and all the steps towards calculating it – when evaluating simulation accuracies of flow over complex terrain.