Turbine Structural Design Margins: How do Recent Siting and Design Trends Impact the Potential for Life Extension?

Description and Background: The commercial and technical trends in wind energy development in North America have been evolving at a rapid pace for over the last two decades. DNV has been a key player in identifying and mitigating the risks inherent during this rapid era of development and accompanying changes. Thus, DNV can offer some perspective on two important recent trends: turbine design and siting practices, and their associated impacts on opportunities for life extension and repowering.
While project developer’s and owner’s expectations for turbine operating life have been increasing, historical excess margins against long term fatigue failure of major structural components (e.g. blades, hubs, shafts, bedplate, tower) have decreased. These excess margins have been in place historically due to the use of more conservative approaches in the design standards and convenient (and conservative) approximations made in design calculations. As computing capabilities and cost competitiveness increases, turbine designers and project developers are using methods that, while allowed by standards and engineering reasoning, do result in a loss of the conservatism that has historically been in place. These loss in conservatism prevent full extrapolation of the historical life extension and repower records of structural reliability and fatigue life. This thus increases uncertainty and risk in aggressively sited projects.
DNV will present the changes allowed by the standard, their impact on the estimated life of components, and the increased probability of failure. There are several steps that can be taken during project development, manufacturing, construction and operation to mitigate the increased uncertainty and reliability proposed by these methods when considering life extension or repowering opportunities.