Offshore Wind Energy – Clean Power from the Sea

Offshore: Great Power Generation off the Coast

The term “offshore” originates from English and means “off the coast”. Accordingly, offshore wind energy refers to the generation of electricity by wind turbines at sea - usually in the North Sea or Baltic Sea. The major advantage: winds are stronger and more consistent at sea than on land. This enables particularly efficient and reliable electricity production. Modern offshore wind farms generate up to twice as much electricity as comparable systems on land. Due to their high utilization rates - offshore turbines continuously feed electricity into the grid for more than 90% of the year - they are considered a  near-baseload renewable energy source. This means that they can guarantee a stable and predictable power supply - and are largely climate-neutral.
Offshore wind power is therefore a central pillar of the energy transition: It is gradually replacing fossil and nuclear power plants and plays a decisive role in making Germany’s electricity supply secure, clean and future-proof.

Photo: © Jan Oelker

Super-Sized Wind Energy

The dimensions of offshore wind turbines are now more gigantic than ever. The total weight of a modern turbine can now exeed 1,500 tons - roughly equivalent to the weight of 1,500 VW Golf cars. In current projects, the foundations (monopiles) alone weigh up to 1,500 tons and reach lengths of up to 100 meters. Monopile foundations weighing up to 2,400 tons are already being developed today. By the end of the 2020s, this weight could even reach up to 3,000 tons.
The nacelles (mashine housings) are also massive: they weigh around 390 tons for 8 MW turbines and up to 520 tons for new 11 to 15 MW classes. The dimensions have also grown to XXL dimensions: the 5 MW turbines installed at the alpha ventus test site had rotor diameters of 125 meters and total heights of over 170 meters above the seabed.
Today, new turbines in the 15 megawatt class have rotor diameters of over 230 meters and total heights of up to 280 meters, which is roughly the height of the Eiffel Tower. This surpasses the wingspan of an Airbus A380 by more than double.
These developments illustrate how much offshore wind technology has grown in recent years - in terms of performance, dimensions and efficiency.

Photo: © RWE | Matthias Ibeler

Large-Scale Renewable Projects at High Seas

The construction of an offshore wind farm is a highly complex large-scale project that brings together a multitude of actors. It can take up to ten years from the initial planning stage through the approval phase and the investment decision to the actual construction of the wind turbines. Not only project developers and investors are involved in this extensive process, but also the subsequent operators of the wind farms. Relevant authorities also play an important role in ensuring that all legal and environmental requirements are met. In addition, numerous manufacturers and component suppliers contribute by providing specialized technologies and materials that are tailored to the extreme conditions at sea. Last but not least, maritime service providers, logistics companies, and port operators are crucial as they provide the infrastructure and ensure the necessary logistics for the transportation and installation of the heavy wind farm components.
Cooperation between these different players is crucial for the successful construction of an offshore wind farm, which not only generates energy but also serves as a milestone for the energy transition.

Photo: © RWE | Matthias Ibeler

Construction Under Extreme Conditions: How Offshore Wind Farms Are Built

Stormy seas, high waves, great depths, and the great distance from the coast make the construction and operation of offshore wind farms particularly challenging. These extreme conditions require specialized technologies, robust materials, and carefully planned logistics - from the first pile-driving operation to commissioning.
The construction of an offshore wind farm proceeds step by step and begins with the so-called foundation installation: Here, the massive monopile foundations - usually made of steel - are driven up to 40 meters deep into the seabed to provide the turbines with long-term stability. In Germany, monopile foundations are used almost exclusively, as the water depths in the North Sea and Baltic Sea are relatively shallow. These foundations offer excellent stability to withstand the harsh conditions for years.
The system components are pre-assembled onshore - typically in large transshipment ports such as Eemshaven, Cuxhaven or Esbjerg - in order to reduce assembly time and weather-related risks at sea. Towers, nacelles and rotor blades are transported to the construction site using specialized ships or lifting platforms. There, the components are assembled step by step using floating crane ships that can stabilize themselves on the water for the work.
Once an offshore turbine is in operation, it must run with high availability and minimal disruptions. This is ensured by regular inspections and maintenance work, during which rotor blades, gearboxes, bearings and foundations are checked. At the same time, specialized control centers on land monitor each individual turbine around the clock via remote access - from performance evaluation to fault analysis.

High Investments - Falling Costs
An offshore wind farm with a capacity of 300 to 400 megawatts requires investments in the billions. Construction at the high seas remains cost-intensive. However, the levelized cost of energy (LCOE) has been falling significantly for years - thanks to technological progress, larger turbines (up to 15 MW), and efficient project planning. And the first projects are already being realized today without government subsidies.
The offshore industry is young, but highly dynamic - innovations such as autonomous maintenance drones, improved planning, and other innovative technologies can further reduce costs in the future and make offshore wind power competitive in the long term.

German law ensures stable compensation for offshore power

In order for renewable energy to expand quickly, offshore wind and other sources receive funding as stipulated in the German Renewable Energy Act (EEG). The law guarantees that grid operators will give precedence to green power in their purchases and provides for a fixed compensation rate over a defined period of time. These aspects give investors and operators greater planning security. There are, however, still risks, such as weather (wind yield) and reliability of the still relatively new turbine technology compared to wind energy on land.

The EEG stipulates compensation for offshore wind power of 15.4 cents per kilowatt-hour for the first twelve years (starting in August 2014). After that, the legally guaranteed rate drops to a quarter of the initial amount (3.9 cents per kilowatt-hour). Wind farm operators also have the option of choosing the "accelerated" model, in which the rate is 19.4 cents per kilowatt-hour initially but then drops to the lowest rate of 3.9 cents per kilowatt-hour after just eight years. Calculated over 20 years, the costs for offshore wind end up being in the middle of the pack relative to all renewable energy sources.

With the EEG 2017, fixed feed-in tariffs were phased out. Support payments are now determined via competitive auctions. At the first auction in 2017, developers bid for projects to be completed in 2021 to 2025. The next auction round starts on January 1, 2021 and will cover projects to be completed in 2026.

Photo: © Jan Oelker

Environmental protection in the spotlight

The use of renewable energy, including offshore wind, is environmental protection in practice. The process of producing such power does not create any harmful carbon; the same cannot be said for fossil fuel sources such as coal, crude oil, and natural gas.

But environmental protection is in the spotlight even when offshore projects are in the construction phase. Considerable effort is made to protect the environment, develop sustainable materials, and design the production processes themselves to be as ecologically friendly as possible. Legal requirements for protecting the marine environment, especially the fauna, are already strict during the approval process for offshore wind farms. In Germany, for example, comprehensive noise control concepts must be presented for the construction phase, especially when the foundation structures are driven into the seafloor, in order to protect porpoises, which are sensitive to noise and protected by animal conservation laws, and other marine mammals.

Grid connection via 'multiple sockets'

Once the offshore wind turbine has been erected and is rotating, the built-in generator can produce electricity. But how does it get to the end user?

Each offshore wind farm has its own transformer platform to which all the turbines are connected in a bundle. Here the electricity is transformed to a higher voltage level for transmission on land. The power lines in the wind farm (internal farm cabling) are three-phase connections. For small and coastal projects, the electricity is fed directly to the next grid node on land via a submarine cable. However, wind farms with higher power and greater distance to the coast would incur very high transmission losses with three-phase technology. For this reason, the so-called cluster connection is used here, especially in the North Sea. This works like multiple sockets. The electricity is fed from the transformer stations of several offshore wind farms to another offshore platform - the so-called converter platform. There, the alternating current from the connected wind farms is converted into direct current and transmitted via a submarine cable to the next grid node on land, where it is in turn converted back into alternating current via an onshore converter. IThis is called high-voltage direct current transmission technology (HVDC). With this technology, significantly morepower can be dissipated per cable. The transmission losses are significantly lower than with three-phase current.

Photo: © Jan Oelker

Offshore wind energy as a nationwide job engine

The expansion of offshore wind energy has great economic potential: total sales along the entire value chain amounted to around EUR 9 billion in 2018. From the development to the operation of an offshore wind farm, actors from different sectors are involved. The offshore wind industry in Germany currently employs around 24,500 people. A stronger expansion of offshore wind energy to 20 GW by 2030 could add around 8,000 jobs.

It is not only the ports and shipyards in the coastal regions that benefit from the economic potential of offshore wind energy. The former are home to the manufacturers of offshore wind turbines and their large components, as well as project developers and logistics companies. But also inland suppliers benefit, e.g. from the metal and mechanical engineering industries, technical service providers, insurance or financing companies, certifiers and consulting firms. Thus, the expansion of offshore wind energy offers growth impulses throughout Germany. The federal states with the highest turnover in terms of added value in the offshore wind energy sector are North Rhine-Westphalia, Baden-Württemberg, Bavaria, Lower Saxony and Hamburg.