The technologies for generating electricity from wind power have seen major refinements over the past decades. With smart systems, new materials, and innovative concepts, they are extracting more and more energy from the wind.
Wind power is one of the fastest-growing sources of sustainable energy. Over the past two decades, the amount of wind energy capacity installed on- and offshore has grown almost 75-fold. From 7.5 gigawatts in 1997 to around 564 gigawatts in 2018, according to data provided by the International Renewable Energy Agency (IRENA). “This technology has made major leaps over the past 20 years. Modern wind turbines generate around ten times as much electricity today as those built at the turn of the millennium,” says Christian Mildenberger. He is Managing Director of the German state of North Rhine-Westphalia’s Association for Renewable Energy (LEE NRW).
Typical turbines in 1985 had a rated output of 0.05 megawatts and a rotor diameter of 15 metres. Today’s models have turbine capacities of around two megawatts onshore and as much as three to five megawatts in offshore versions. New turbine classes boasting outputs of more than seven megawatts are already planned. They will be ready to deploy in three to five years.
Using wind power correctly
In order to maximise their energy yield, turbines need to be controlled. Such that they can adapt to changing wind conditions. To this end, control systems process a variety of data supplied by all kinds of sensors. For instance, absolute encoders record rotor blades’ angle of attack, while incremental encoders measure rotors’ rotational speed.
In order for the correct settings to be adopted in good time LiDAR can be used to measure the wind’s speed and direction. During this process, LiDAR devices emit laser beams that are reflected by particles blowing in the wind. The turbine therefore “knows” what kind of wind loads will reach it imminently (i.e., in the next few seconds).
More efficient power conversion
The converter is another important element when it comes to increasing a turbine’s efficiency. Nowadays, most wind turbines are operated with a variable rotor speed. As such, the generator supplies electricity with variable frequencies and voltages. The power electronics in the converters control. And regulate the generated electricity such that it can always be fed into the mains with the appropriate grid frequency and quality. Future technologies promise to double the power density in the semiconductor module. Which will enable the converter’s volume to be reduced considerably. In addition, power electronics with a silicon carbide (SiC) base promise major improvements. SiC MOSFETs achieve high switching frequencies, which in turn enables smaller filter components to be used. At the same time, switching losses can be reduced, higher power densities achieved, and overall system efficiency increased.
One downside of wind turbines is that many bats are killed by collisions with rotor blades. That’s why ultrasound detectors are being mounted to the turbines to detect bats’ echolocation calls when they fly within the rotor blades’ risk zone. Together with meteorological data, threshold values for the temperature and wind speed can be calculated to ensure that the wind turbines’ operation poses no threat to bats. In this case, wind turbines will only produce electricity when there are few active bats or none at all.
AI helps to avoid downtime
Electronics also play a crucial part in keeping wind turbines in operation for a long time while remaining economical. Thanks to ever-higher levels of connectivity and digitalisation, it is even possible to monitor operating parameters in real time. Artificial Intelligence (AI) is increasingly being used in the process. All relevant parameters and measured data within an entire wind farm are gathered and processed in order to recreate the current operating and maintenance state of the individual turbines. To perform this task, the AI learns to recognise indicators such as specific vibrations or component temperature increases as symptoms of damage. With this information for example, it is possible to determine whether certain components will soon fail, and to replace them before an entire wind turbine goes offline.
Furthermore, the operational management systems in individual turbines can be coordinated with one another. One benefit of this is enabling turbines arranged in series to be aligned such that they extract as much power from the wind as possible.
Innovative concepts with wind power
A wind turbine design featuring a horizontal axis and rotor blades has become the most widespread worldwide. Yet more “traditional” rotor models could face stiff competition from a number of exciting projects. To name one example, start-up company Vortex Bladeless has developed a concept that manages perfectly well without rotor blades or turbines. The systems essentially consist of a column made to vibrate by the wind. In turn, these vibrations are then converted to electricity by a generator. Vortex Bladeless estimates that the electricity generated by such vertical systems could be 40 per cent cheaper than that gained from conventional wind turbines. However, the power yield from this innovative design is considerably lower than traditional models.
The airborne wind energy systems developed by SkySails Power are based on an altogether different principle. Driven by the wind, automatically controlled power kites rise in figures of eight. As they gain altitude, they unwind a tether from a winch, and the connected generator then produces electricity. As soon as the tether has reached its maximum length, the retraction phase begins. The kite automatically returns to a position where its traction is very low, enabling it to be recovered without much resistance. The generator then acts like a motor to reel the tether in.
This retraction process requires a fraction of the energy generated during the work phase. “The systems operate extremely quietly, are inconspicuous in the landscape, and cast barely any shadows,” says Stephan Wrage, CEO of SkySails Power. As he explains, these advantages can help to increase the acceptance of wind power even further. “This all makes SkySails’ technology a fascinating concept for renewable power generation using wind energy,” Wrage adds.
