Constellation, le dépôt institutionnel de l'Université du Québec à Chicoutimi

Résumé

Cup anemometers are used in the wind energy industry to characterize wind farm sites and to predict monthly and annual energy production. Their role is important since wind speed predictions depend on their correct operation. Unfortunately, northern climates greatly affect the performance of anemometers, because in-cloud icing generally occurs at higher altitudes (more than 600 m). Wind speed prediction error caused by rime ice accreted on the anemometer can be as large as 10 % to 30 % during the winter months. This generates big errors in wind predictions, resulting in an undervaluation of the wind potential of a site or causing overloads to the wind turbines which depend only on the parameters read by the anemometer. In order to partially remedy this difficulty, heated cup anemometers are used. The Anti-icing Materials International Laboratory (AMIL) at the University of Quebec at Chicoutimi (UQAC), in collaboration with the Wind Energy Group at the University of Quebec at Rimouski (UQAR) evaluated, in a refrigerated wind tunnel, under a very severe freezing fog, the behaviour of two cup anemometers in order to estimate and model the performance loss in adverse atmospheric conditions. The results obtained show that performance decreases for both unheated and heated cup anemometers with respect to exposure time and freezing fog severity, leading to complete stoppage of the unheated anemometer. Finally, a semi-empirical equation, taking into account air speed and temperature, liquid water content as well as water droplets median volumetric diameter is proposed in order to predict a cup anemometer’s performance loss due to exposure time to freezing fog exposure time.