Poor site design can cause underperformance at individual turbines of 50 percent and more

The solutions tailored for wind farm designing and optimisation continue to evolve.

Such applications now have various striking features be it for their architecture patterned after geographical information systems, allowing for complex exclusions and setbacks to be designed easily for the most challenging sites, or for allowing combination of several different data types using simple logical operations, allowing complex site configurations to be assembled in minutes.

As a specialist, Natural Power has developed a thorough project design and optimisation process that ensures all projects strike an appropriate balance between optimal energy production and sensitive site design.
Renewable energy projects in which the company has been closely involved, such as the 50 MW Crystal Rig 1 site in the Scottish Borders, all follow this process. The balance of technical and environmental considerations focuses on economic return, technical feasibility and the probability of acquiring environmental approval and building consents.

Speaking with windenergyupdate.com on the significance of the same, Oisin Brady, senior technical manager, Natural Power, says, "Good site design means siting turbines where wind flow conditions, including wind shear, turbulence and inflow angles are as close as possible to design conditions. This requires knowledge that can only be obtained with high-density well-instrumented measurement campaigns and/or CFD calculations.  Only in these conditions will the turbines perform as expected both in terms of performance and maintenance costs."

On the other hand, Brady, who is scheduled to speak during windenergyupdate.com's Wind Energy Performance Optimisation Summit (to be held on 11th - 12th February 2009 in Hamburg, Germany), says poor site design has been shown to cause underperformance at individual turbines of 50 percent and more compared to budgeted and significantly increased maintenance costs.  

"In extreme cases, the site was inoperative and the turbines have had to be moved.  In other cases, CFD tools identified potential solutions through removing areas of forest which were disturbing the flow into the turbines," says Brady.

A section of the industry says to increase the prediction quality for extension of wind farms or replacement of turbines, emphasis should be put on the improvement of modelling the power output of individual turbines of a farm.

Specifically on selection of correct tools to diagnose underperformance of wind farms and the challenges associated with it, Brady said analysing operational wind farms requires detailed SCADA analysis, such as Natural Power's Melogale, to perform root-cause analysis for downtime.  

"Once reasons for downtime have been identified, further action can be taken.  If the cause is related to wind conditions, CFD tools or remote sensing can be used to examine inflow conditions and identify mitigation measures.  Such techniques however require experienced use as it can be easy to draw incorrect conclusions," said Brady.

One of the major concerns in investing in wind turbines and wind farms are related to the availability of the turbines, i.e. the risk of having less wind power production from the wind turbines due to stand still and repair. Reliability of the structures and the wind turbines is therefore essential for the wind farm to perform successfully.

On which is the best way to place and use the information from permanent masts for wind farm efficiency, Brady said correctly-sited permanent masts are placed so as to benefit from predominant winds while not being subject to turbine wake.

"They offer an independent measurement of wind speed and climatic conditions, unaffected by rotor and nacelle blockage.  As such, when combined with standard calculation tools, they allow turbine performance to be closely tracked.  If equipped with a logging system independent from the SCADA, they are invaluable for determining downtime compensation in the event of grid outage."

The companies also need to plan performance analysis and optimisation to ensure analysis of turbine performance.  

While third party SCADA systems exist, frequently the standard SCADA datasets available to operators, when combined with meteorological and site intervention data, contain enough information to perform in-depth analysis of turbine performance.  

"However, processing this information requires dedicated staff and ultimately requires accumulated skill and experience," pointed out Brady.

On whether assessing the performance of a wind farm is for many owners a task performed at best on an annual basis with only the reports produced by the turbine manufacturers' own SCADA system and metered output as a source of information, Brady said unfortunately many wind farms are currently operated on such basis.

On the positive side, increasingly, large utilities are using in-house skills, or dedicated control room facilities to monitor sites on a real-time, weekly or monthly basis.  

"Using third parties carries extra weight particularly where claims for liquidated damages are concerned.  As portfolios are increasing consolidated into fewer hands, it is expected that this trend will continue," said Brady.