Challenges and Potentials in the Integration of Offshore Wind Energy and Hydrogen Production

In the last decade, hydrogen technology and offshore wind energy have experienced a remarkable upswing. By integrating these two technologies, advances in the energy system and decarbonization can be achieved.

For a long time, the use of hydrogen - either as a direct fuel or in a fuel cell – or as an alternative to fossil fuels has been praised. But now hydrogen made the breakthrough and established itself as a core element of the energy transition. Its importance is based on three characteristics [12]:

• Potential for decarbonization of energy intensive sectors (steel, chemicals, etc.)
• Can be stored flexibly as an energy carrier (e.g. in salt caverns, storage tanks or pipelines)
• Transportable with high volumetric energy density (e.g. as compressed gas or liquid form)

Green hydrogen will play a central role in achieving global climate goals. Therefore, its production must be scaled up. According to the calculation basis of the Net Zero Emission Scenario, about 500 Mt of hydrogen per year will be needed in 2050, while the current production volume is about 100 Mt per year [5]. In the future, most of the hydrogen should be produced by electrolysis. The electricity required for this could be provided by offshore wind energy.

Many countries consider offshore wind as a core element of their decarbonization strategy. Keeping the goal of climate neutrality in mind, the European Commission has decided to install 300 GW of offshore wind capacity in Europe until 2050. [9] For China, offshore wind is also a core topic in the 14th Five-Year-Plan that covers the development strategy from 2021 to 2025. Many provinces have published quantitative targets in this regard. For example, Guangdong Province aims to expand offshore wind capacity to 18 GW until 2025 [10].

The integration of hydrogen technology and offshore wind energy require innovations in the following areas:

1, Development of floating offshore wind energy

2. Development of offshore electrolysis

3. Cost reduction

Development of Floating Offshore Wind Energy

Only 5% of the world's electricity is generated by wind power, with most installations located onshore. Since wind speed at sea is usually higher and more constant, wind turbines installed offshore can theoretically generate more power. The diagram below shows the relation between wind speeds and the electricity that can be generated, referring to a 6 MW wind turbine. Starting from a wind speed of about 11 m/s, which corresponds to wind force 6 and is referred to as "strong wind", the turbine reaches its rated power. This range is reached more regularly by offshore wind turbines. In the North Sea, around the equivalent of 4000 full load hours can be achieved annually, in best offshore locations this value surpasses 6,000 hours. As a rule of thumb, we can say, the further offshore the wind park location is the more hours are possible.

There are several ways to install offshore wind turbines. When the sea depth is up to 60 m, the wind turbine is fixed to the seabed with fixed substructure. However, about 80% of offshore wind resources have water depth greater than 60 m [2]. In this case, floating solutions are chosen for economic reasons. For example, wind turbines with the "Tension Leg Platform" can be installed up to a sea depth of 2,000 m [3].

Pilot projects for floating offshore wind energy are increasingly being launched. For example, RWE and Saitec Offshore Technologies announced the joint realization of a floating offshore wind turbine in February 2020. [7] In the pilot project "DemoSATH", a floating offshore wind turbine with a rated power of 2 MW will be installed around 3 km off the Basque coast in Spain at a water depth of 85 m. The start of the project is scheduled for Q3/2022. [8]

Development of Offshore Electrolysis

Three concepts for combining offshore wind energy with hydrogen production will be discussed.

Centralized Onshore Electrolysis Using Offshore Wind Energy:

In this concept, the electricity from the offshore wind turbines is transported via cables to an electrolyzer located onshore. The water for electrolysis could be provided by a local supplier. If the offshore wind turbines are located far offshore, this concept may be unprofitable since energy losses in the HVDC cable and cost increase with distance.

Centralized Offshore Electrolysis Using Offshore Wind Energy:

In this concept, the electrolyzer is installed offshore, e.g. on a vessel, and is connected to the offshore wind turbines via power cables. The hydrogen produced is compressed and then transported to shore via pipelines. The pipelines are less expensive than power cables for long distances and have a service life of 40 to 80 years [4].

Decentralized Offshore Electrolysis Using Offshore Wind Energy:

The offshore wind turbines are each connected to an electrolyzer. The electricity generated is used directly to produce hydrogen decentral, which is then compressed and transported to shore via pipelines. The main advantage of this concept is the resilience induced by decentralization, i.e. if one electrolyzer fails, hydrogen can still be produced by the remaining electrolyzers.

A key differentiator between the concepts is the energy vector: While centralized onshore electrolysis uses power cables to transport offshore wind energy to shore, offshore electrolysis concepts use hydrogen as an energy carrier (33kWh/kg) and transport it to shore through pipelines. Over long distances and at high mass flows, hydrogen is the more economically viable alternative. [18]

Pipelines for transporting hydrogen are already in practical use. For example, there are 2575 km long pipelines for hydrogen transport in the USA. Germany has about 400 km of pipelines [4]. Due to the very low molecular mass of hydrogen, reciprocating compressors like piston and diaphragm compressors are chosen to generate the required pressure in the pipelines.

The offshore application sets specific requirements on the piston compressor. For example, the piston compressor must be designed to be resistant to rusting due to the humid and salty conditions. Furthermore, wave motions must also be considered, which could influence the piston and piston rod seals.

Cost Reduction

Offshore wind energy offers great potential for green hydrogen production. Floating approaches are also promising for exploiting more constant and higher wind speed. But for widespread expansion of offshore wind energy, costs must be further reduced. Various approaches exist for this purpose: Besides reducing unit costs through product standardization, the integrated design is another solution approach. In cooperation with other companies, NEUMAN & ESSER is already developing concepts for the integrated design of a "Floating Offshore Windenergy-Based Hydrogen Production". Here, the wind turbines, the electrolyzer, the piston compressors, the electricity and hydrogen flows in the pipelines are analyzed and optimized in models so that the global optimum is achieved over the life cycle. As a result, the levelized cost of energy (LCOE) can be reduced.

According to studies, the market for floating solutions will be larger than that with fixed substructure. Currently, the LCOE for the floating solutions is 175 €/MWh, while it is 90 €/MWh for the fixed substructure solutions [1]. Both solutions are expected to converge against 35 €/MWh by 2050 [1].

Prediction of Offshore Wind Energy and Conclusion

Industrialized nations in Europe, such as Great Britain and Germany, have possessed the largest installed offshore wind capacity for a long time period. Recently, countries in Asia-Pacific have caught up quickly, especially China and Vietnam. In 2021, China was responsible for 80% of new offshore installations and now has 48% of global installed offshore wind power.

Based on studies, global installed offshore wind capacity is expected to reach 630 GW by 2050, up from 55 GW in 2021, with an upside potential of 1,000 GW in a 1.5° scenario. [6], [11]

In the future, thousands of offshore wind turbines will spin and generate energy off the coasts of Asia, Europe, North America, and other regions. This energy will be used to produce green hydrogen, which is essential for making the energy system more flexible and robust to effectively decarbonize the economy.