Each wind turbine has an individual lifetime which is affected by the on-site wind conditions. Parameters like wind speed, wind shear, turbulence, air temperature, salinity, etc…can differ significantly from site to site. Understanding the differences between the design loads and the actual loads on-site and their impact on turbine and components can lead to a greater understanding of the assets risk and potentials. On one hand, performance, operational and financial risk can be anticipated and avoided, some of those that could even lead to catastrophic failures. On the other hand, the possibility of prolonging the operational time of the wind turbine past is design life time can also be attested, with obvious economic and financial benefits.
In Brazil, conditions are very different from those found in Europe and United States, for which most of the turbine models where initially developed and tested. Owners and authorities should be aware of this. Using an analytical approach, the lifetime of each wind turbine main component can be calculated.
Utilizing an aero-elastic simulation, the individual overall lifetime can be calculated per main component. In most cases, the lifetime of the asset can be extended. However, even with a permit to prolong the operation, you will have to clarify further economic question before you continue to operate. You have to show your understanding of the corresponding effects on the O&M concept for old wind farms.
Based on more than 500 lifetime extension (LTE) assessments, the first results and challenges will be outlined. We will outline the key points and discuss this from a practical experience from the field. This offers a real benefit in comparison to the research topics for LTE and the theoretical papers currently in discussion.
The weak points of a wind turbine can be determined and the risk of damage caused by fatigue can be reduced. Knowing the overall lifetime serves as a basis for reliable organizational and financial decisions.
Moreover, the analysis helps to estimate financial and structural risks when the conditions on-site change e.g. in the case of new wind farms built in the direct vicinity of existing ones. The new wind turbines influence the turbulence on-site and causes wake effects. This might lead to lower energy yields of the existing wind turbines and even influence the structural safety in a negative way. This aspect should also be of major concern to Brazil as many wind farm clusters of several hundreds of turbines are being developed by different companies, in proximities as close as a few kilometres, particularly in the North-eastern states.
In addition, the results of the simulation can be used to give advice on how to operate a wind turbine more safely and adjust it to the individual on-site conditions.
Also, the individual maintenance plan can be adjusted according to the lifetime of the main components and repairs of critical components can be planned in a long-term schedule. During regular inspections, it is possible to check the weak points, e.g. the rotor blade connection, more closely and notice anomalies at an early stage. To extend the lifetime of the wind turbine it is possible to adjust the operation mode and/or renew the affected component.
During the discussion with wind farm owners and operators and project execution of hundreds of lifetime extension assessments, the following challenges appear to be the most relevant:
- Lack of real knowledge of each wind turbine’s actual site conditions and how they fit the turbine’s and components design criteria;
- Difficulty in knowing what operational settings, retrofits, repairs, etc…need to be done to ensure the planned lifetime and what are the impact in operation and performance;
- Collection of data (retrofits, tracked repairs and other rather old documentations) - Inconsistent calculation approach within the industry and heterogeneous expectation by local bodies
In summary, each wind turbine has its individual lifetime which can be analyzed based on the onsite wind conditions. Thus, the analysis enables operators, project developers and investors to plan individually and with a high reliability. However, without outlining an operation strategy for aging wind farms, the capability to achieve and prolong the planned lifetime of your turbine is just a first step for a financial decision to continue operation.