Posters

Abstract

The energy loss associated to the blade degradation of the wind turbines is becoming an important step in the long-term energy assessments calculations due to the wide diversity of sites and environmental conditions as well as longer estimated lifetimes. The accumulation of material on the blades (soiling) and loss of material (erosion) through the life of the blades results in a reduction in the blade aerodynamic efficiency. A blade surface that has accumulated soiling, leading edge erosion, or both will therefore experiment lower performance. Soiling occurs during operation of the blades as objects/particles in the atmosphere impinge on the blade, leaving residual material on the blade surface.  Leading edge erosion occurs as rain, hail, and other particles impact with the blade surface causing microcracking and fatigue-like damage to the structure.  The effect is typically insignificant in short timescales, but through the life of the turbine becomes important specially if maintenance and correction measures are not in place. As both effects occur progressively, observing and quantifying it in operational wind farms becomes extremely difficult. Experiments to blade profiles in wind tunnels are conducted in extremely theoretical conditions that hardly represent real environment where wind farms operate.  Hence, a pragmatic approach remains necessary to account for this loss.  A constant yearly degradation loss is commonly used to estimate the future losses of a site. However, this constant degradation is very simplistic and does not consider the specifics of the site,  the repair strategies or the impact of the leading edge protection solutions. DNV has reviewed the available bibliography consisting in operational experience from operation wind farms, theoretical experiments and own experience and proposes a reviewed methodology that includes learning from the last years. As a result, five turbine performance degradation loss factor profiles have been incorporated to address lifetime blade degradation loss in energy production assessments.  Similar to legacy approaches, the degradation loss factor profile shall not represent a site-specific calculation, but a degradation assumption for the project in question. The work presented shows the key drivers of the degradation of the blades, how they are combined to obtain a degradation profile and which losses will occur on site for an specific long-term scenario.