Question of the Week: Stiesdal, DNV GL and PMSS on recent advances in wind?

This week Windpower Monthly asks Henrik Stiesdal of Siemens, Tony Mercer of DNV GL and Alan Chivers of TUV SUD PMSS where the industry has made the most significant leaps forward in recent times.

Stiesdal holds that turbines' improved compatibility with grid codes is wind's greatest advancement
Stiesdal holds that turbines' improved compatibility with grid codes is wind's greatest advancement

Question: What has been the most significant technological development related to wind turbines of the last ten years?

Henrik Stiesdal – CTO Siemens Wind Power

The most significant technological advancement over the last ten years is how turbines have become compatible with grid codes.

All the early wind turbines were required to get off the grid in the case of disturbances. However, around 2002 it was realised by some utilities, primarily E.on and Scottish Power, that this strategy was not viable in the long term. Once wind turbine share of the overall supply got above a certain threshold, disconnecting them in case of faults would lead to a collapse of the grid.

Hence, the requirement went through a complete reversal. Wind turbines needed to stay on line, essentially no matter what, and they also needed to provide reactive power support. This was a substantial challenge to the industry, but it took it with a straight back, and before the turn of the decade turbines could basically be set up to meet even the most stringent requirements of the system operators.

This technological advancement took us from supplying simple "energy machines" to machines that can function as genuine power plants. The only thing left now is utility-scale energy storage: once we have that in place, offering dispatchable wind power, nothing speaks against substituting conventional power with wind!

Tony Mercer – head of turbine engineering control DNV GL

Over the last ten years the concept of controlling each of the turbine's blade pitch angles individually, Individual Pitch Control (IPC), has moved from R&D to reality and is now deployed across a small but notable section of the industry.

The technique uses the latent pitch system capability inherent in almost all modern pitch controlled turbines to fly each blade along a minimum load path as it spins through complex three-dimensional wind turbulence structures. This can reduce thrust-related fatigue and extreme loading on the blades, across the rotor and thereby also the consequential bending moments experienced by the support structure.

At today's 3MW scale the technique has potential to increase energy capture by more than 10% for a smaller increase in turbine cost.

That said, this potential is far from fully realised. The big benefits accrue when it's fully integrated into blade, pitch system and turbine concept design, and much remains to be done in these areas. The time for this is now; the market in general is becoming more sophisticated, design and certification processes are beginning to internalise and accommodate clever control, and the supply chain is building new competence with the unique and troublesome challenges of reducing wind turbine lifetime costs.

Alan Chivers, chairman TUV SUD PMSS

While the development of 7MW and 8MW offshore giants continues to make the headlines, the most significant advancements in wind turbine technology have really little to do with scale. Instead, they're about progressive improvement and optimisation of performance and efficiency within the operational environment thereby boosting long-term availability.

In offshore wind, for instance, the successful marinisation of technology originally designed for onshore applications has been crucial. It was not simply a question of taking an onshore wind turbine and bolting it to an offshore foundation, more a case of  ensuring that all materials were appropriate to the environment. This has been a key achievement.

Across the board, efficiency has been boosted by the deployment of remote capabilities. The ability to forecast and adapt on the basis of the weather ensures a steady output, while malfunctioning machines can often be diagnosed, in some cases fixed and restarted remotely, meaning that time is saved in transporting technicians to and from the turbines unnecessarily.

When the time comes to manually access a turbine, modern access systems are safer and more worker-friendly than ever before, simplifying one of the more problematic project interfaces. Lifts for example mitigate many of the long-term health issues that may arise from excessive ladder climbing, also improving worker productivity by reducing fatigue.

The improvements in efficiency, accessibility and operability clearly correlate with relative improvements in turbine availability – and therein lies the greatest achievement of the past ten years.

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