Wind Energy – The Heavenly Resource

In fairy tales of old, wind is considered a heavenly child, but in times of climate change it’s becoming an indispensable resource. Europe, it has long been clear, needs more wind energy. But how can this potential best be harnessed? On land or at sea? DEKRA solutions has taken a closer look at current technologies and projects.

The Kriegers Flak wind farm is located 15 to 40 kilometres off the Danish coast in the Baltic Sea and covers an area of 132 square kilometers. Photo: Kriegers Flak

The EU Commission’s European Green Deal is in dire need of support from heavenly powers. After all, the climate law approved by the EU Parliament in June stipulates that greenhouse gas emissions in the Union must be reduced by 55 percent compared to 1990 levels. Ultimately, these targets can only be achieved through the consistent use of wind energy or, more precisely, through the wind’s kinetic energy that produces electricity. As the European industry association Wind Europe recently stated in Brussels, it’s high time for the EU to greatly increase the expansion of its wind energy capacities in order to achieve the climate target – from 15 gigawatts (GW) last year to at least 30 GW installed year after year in the future (total capacity onshore and offshore in the EU 2020: around 220 GW). These are ambitious goals for the wind industry, especially since landscape and environmental protection as well as lengthy approval procedures repeatedly take the wind out of new wind turbines’ rotors in many European countries. Nevertheless, chances are high that wind power generation can be increased. Highly efficient turbines will play a role in this.

Wind Turbines increase significantly in Size

Across the country, startups are experimenting with innovative airborne wind turbines that climb to altitudes between 200 and 400 meters to harness the high-yield high-altitude winds for electricity production with the help of generator rope winches. However, there’s more development work that needs to be done before these turbines can make a significant contribution. For the time being, the main burden of power generation lies with the classic onshore wind turbines that include a tower, nacelle, and rotor. These systems have become much more efficient in recent years. A study published in October 2020 on behalf of the German Wind Energy Association shows that modern onshore wind turbines now produce around ten times as much electricity as they did 20 years ago. This increase in output was made possible primarily by significant growth in turbine size – the average rotor diameter has roughly doubled from around 60 meters in 2000 to 2019. Today, rotor diameters range between 133 and 170 meters. Hub heights vary between 90 and 166 meters and the rated output of larger turbines is 6.6 megawatts, while smaller units produce around four megawatts. But what are the bottom-line benefits of these characteristics? Using Germany as an example, the authors of the wind energy study come to a clear conclusion: By using modern wind turbines, wind power generation could be doubled to more than 200 terawatt hours (TWh) by 2030 – which would correspond to around 40 percent of electricity demand – on the areas designated for wind energy in Germany alone.

For Wind Farms, less is sometimes more

DEKRA Expert Christian Leward. Photo: DEKRA

At first glance, it seems sensible to design wind farm capacities as generously as possible. However, planning according to the motto “more is better” can lead to incorrect calculations. The expected higher electricity yield is countered by physical and economic laws, as DEKRA expert Christian Leward explains. The Swede is Director of Wind Energy in the DEKRA Service Division Industrial Inspection. DEKRA supports installers and operators of wind turbines in all project phases with comprehensive consulting and testing services – including material selection and development, certification and approval procedures, accompanying tests and inspections during the erection phase, all the way through to commissioning and operation. “If several turbines are positioned behind each other downwind in a wind farm, this can result in mutual shading. They take wind away from each other and can’t perform to their full potential,” Christian Leward knows. For smaller areas, it can therefore make sense to reduce the number of turbines if this improves the efficiency of the overall system.

The Future of Wind Energy probably lies on the Water

Source: Wind Europe

But perhaps the future of wind energy doesn’t lie on land at all? When installing new capacities, more and more turbine manufacturers and electricity producers are drawn out to sea, where strong winds blow undisturbed across the water. Experts believe that wind turbines at sea generate around 20 percent more electricity than comparable turbines on land. Manufacturers are already pushing into incredible performance spheres with their offshore turbines. The international front-runner is a prototype from General Electric Renewable Energy: The Haliade-X-14 MW, equipped with three rotor blades, each 107 meters long, rises 260 meters into the air and generates a nominal output of 14 MW – one rotation of this turbine’s rotor is enough to supply a house with two days worth of energy. In fact, the European Union sees offshore technology as a major future component of Europe’s energy system. By 2050, the EU aims to install 300 GW of offshore wind power capacity using ground-based and floating turbines. So far, offshore turbines dominate at sea, anchored in shallower coastal waters up to 50 meters deep with elaborate foundations in the seabed. However, only about five percent of marine areas are suitable locations for these technologies. There are currently 12 GW installed with this technology in EU waters. In future, the electricity yield could be even better with floating wind turbines – they can be deployed at ocean depths no longer accessible to conventional offshore technology. At the moment, the portfolio of floating turbines is still manageable – the installed capacity in the EU is around 40 MW. However, several member states have already announced larger projects.

Overview: Important Offshore Projects yesterday, today and tomorrow

Alpha Ventus – The Age of Offshore Wind Energy began ten years ago

Alpha Ventus, the first offshore wind farm in Germany, went into operation in the German Bight back in the spring of 2010. The wind farm, installed at a water depth of around 30 meters and located 65 kilometers off the coast, consisted of turbines with a rotor diameter of 126 meters and a hub height of 93 meters. By 2019, the wind farm had fed as much electricity into the grid year after year on average as 57,000 average households in Germany consume. Currently, wind turbines with a capacity of around 6,700 MW are installed in the German Bight.

East Anglia One off the British East Coast – One of the largest Wind Farms in the World

One of the world’s largest offshore wind farms is located 43 kilometers off the British east coast on a level with the county of Suffolk. Covering an area of around 300 square kilometers, East Anglia One comprises 102 wind turbines with a rotor diameter of 154 meters and a total capacity of 714 MW. The turbines are located on a 65-meter-high, three-legged steel platform weighing over 800 tons, which extends 45 meters down to the seabed. East Anglia One was completed in July 2020 and is the first of four farms to be built in the region with a capacity of 3,500 MW.

Kriegers Flak off the Danish Coast – The largest Wind Farm in Scandinavia

Denmark commissioned the Kriegers Flak offshore wind farm in early September 2021. The wind farm is located 15 to 40 kilometers off the Danish coast in the Baltic Sea and covers an area of 132 square kilometers. The facility consists of 72 wind turbines with a rotor diameter of 167 meters and total height of 187 meters. The foundations weigh up to 800 tons each. With an installed capacity of 604 MW, Kriegers Flak is considered the largest wind farm in Scandinavia. It’s expected to cover the annual energy consumption of around 600,000 Danish households.

Floating Wind Farm Hywind Scotland

The world’s first floating wind farm is the “Hywind Scotland”, which opened in 2017 and is installed around 30 kilometers off the coast of Scotland in a water depth of 95 to 120 meters in the North Sea. The park, which covers an area of around four square kilometers, consists of five wind turbines, each with a tower almost 100 meters high and rotor blades 75 meters long. The total capacity of the plant is 30 MW. The turbines sit on floating bodies around 90 meters long and weighing 3,500 tons, which are held in position by steel chains.

Wind Turbine “Nezzy²” learning to swim in the Baltic Sea

Test model of the floating wind turbine “Nezzy 2” in a storm near Vierow in Mecklenburg-Western Pomerania. Photo: Jan Oelker/aerodyn

The Nezzy² research project of North German engineering company aerodyn engineering consists of two wind turbines on a floating foundation made of precast concrete elements, which aligns itself independently with the wind flow and is anchored to the seabed with six lines. The two wind turbines are supported by two towers set at an angle in the center of the foundation. Nezzy² currently exists only as a 1:10 scale model 18 meters high, which recently successfully passed a two-month test in the Greifswalder Bodden in the Baltic Sea. A full-scale prototype is scheduled to make its debut off the coast of China in early 2022. An output of around 15 MW is planned.

Windcatcher from Norway

The Windcatcher from Norwegian company Wind Catching Systems, founded in 2017, is a square lattice tube frame with a side length of around 320 meters, which is fixed to a floating body anchored in the seabed. Around 100 small rotors are mounted in this framework, which together deliver five times as much electricity as the largest wind turbines. Compared to conventional turbines, the Windcatcher takes up only one-fifth of the surface area. At the same time, it has a larger effective range because the smaller rotors produce electricity at full power even at wind speeds beyond six Beaufort. So far, the spectacular project exists only in simulations; the first prototypes will be deployed next year.

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