Viewpoint: Turbines may look alike but progress continues

When I started in the wind industry in the late 1980s, wind turbines came in many forms -- vertical and horizontal axis, one-, two- and three-bladers, stall regulated, partial- or full-span pitch control...

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Looking back, the contemporary onlooker might say modern turbines all look the same, and, in technological terms, that this has become a boring industry to work in.

I disagree. Wind turbines combine flexible structures with dynamic machines operating in a complex, time-varying environment. In what other industry does a designer need to have an understanding of meteorology, aerodynamics, composite materials, mechanical systems, civil structures, electric machines, and transmission and distribution assets?

Where else would you be in day-to-day contact with experts in all those fields of science and engineering? And where else could you so directly contribute to a sustainable industrial future? Meeting the challenge of generating energy at ever lower costs while dealing with the extreme environments that wind turbines have to operate in remains both fascinating and rewarding.

Concept pioneers

In those early days, designers were still looking for the best way to extract energy from wind. The diversity of options they considered hampered progress, as all came with their own challenges.

Converging on one high-level concept was an essential step in the development of wind power towards its acceptance as a mainstream generation technology. It did not signal a slowdown in the pace of technological innovation. It simply provided a clearer focus.

The pioneers of modern wind energy were mainly found in two camps. First, enthusiasts mainly in Denmark developed turbines that applied technologies from boat-building and agriculture. Second, large-scale government-funded research programmes employed the likes of Boeing, Grumman and BAe to develop multi-megawatt machines utilising aerospace technologies.

The early adoption of wind in small community projects meant the bottom-up technology approach was initially more commercially successful.

However, as the turbines increased in scale (mainly driven by political demand) the levels of investment in technological improvements increased, and these two camps merged into one, bringing together the strengths of both.

The main challenge was to reduce capital expenditure, which required that designers beat the square-cube law: simple upscaling of technology results in power increasing with the square of the rotor diameter, while weight (and therefore cost) increases with the cube. The bottom-up "learning by doing" approach worked well for designs up to around 500kW, at which point the three-blade upwind concept was firmly established.

Further improvements in technology, which allowed turbines to grow into today’s multi-MW giants, required a thorough understanding of the loading, aerodynamics and material properties. The foundations for much of this learning were put in place by the large government-funded programmes that included much measurement activities, and kickstarted the development of numerical models.

The application of this understanding has resulted in lighter, more efficient designs, which, coupled with increased production volumes, has brought costs down while turbines have grown in size.

Cost focus

Today, the focus has shifted to minimising the levelised cost of energy, with the designers of large-capacity turbines benefiting from decades of practical experience and research effort.

Turbines are designed using the same computational tools and to the same tolerances as those of aerospace or Formula 1 racing cars, offering opportunities to deliver cutting-edge innovations. Universities are becoming ever more aware of this reality, with many now offering modules that focus on the specific needs of wind-turbine or wind-farm design.

Increasingly, turbines are becoming covered in sensors that measure the loading of critical structures and the performance of many components. The information is then fed into the control systems, so that turbines are operated to balance the often-conflicting demands of energy production and load mitigation.

As recently highlighted by the International Energy Agency’s Next generation wind and solar power report, the next phase of wind’s development will require it to move beyond a focus on cost and instead consider what value it can offer the energy system as a whole.

Operating arrays of turbines as power stations that can offer ancillary services to the grid will require further innovation. While it is unlikely that the casual observer will see a major shift in turbine topology, it is certain that we will see significant shifts in what is "under the bonnet".

Robert Rawlinson-Smith is service area leader and innovation manager, renewables advisory at DNV GL-Energy

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