Wind turbine performance fluctuates between the winter and summer months. A difference of 5-10% between the power curves can be observed, and it can even exceed this.

This is due to the effects of wind shear, turbulence and atmospheric stability. As a result, production estimates can be highly uncertain.

Depending on atmospheric conditions, wind turbines often operate in far from ideal conditions and actual power curves may be very different from those certified.

Atmospheric stability is a measure of vertical turbulence in the atmosphere (near the Earth’s surface) that reflects the extent to which the vertical motion of air in the atmosphere is strengthened or suppressed. Vertical movements are reinforced in an unstable atmosphere. The unstable layers of vertically moving air (up or down) are therefore amplified. Stable air layers therefore tend to remain at their altitude.

Studies have shown that the power generated at a given wind speed is higher in stable and lower conditions under conditions of high convection – the average power difference is around 15%. Or that, an estimated annual production without filter on atmospheric conditions or turbulence is greater than any production calculated with these filters. The effects of these atmospheric parameters can therefore be considerable.

Marion Cayla – Technical Asset Manager