An offshore wind and hydrogen marriage comes with big and expensive choices

Developers are understandably attracted by the concept of pairing electrolysers with offshore wind farms to produce green hydrogen at sea. This combines the promise of abundant offshore renewable energy with hydrogen's versatility, with potential usages spanning from electricity generation and alternative fuels production to ammonia creation for the fertiliser industry.

Deployment of electrolysers alongside offshore wind has its challenges, however, from high capital costs to safety concerns. Offshore-produced hydrogen must compete with onshore production that benefits from lower infrastructure and maintenance costs, and the economics behind green hydrogen more generally are challenging.

The offshore wind-to-green hydrogen concept is straightforward. It entails placing electrolysers at offshore wind farms, where electricity generated from renewable sources will be used to split water into hydrogen and oxygen. Currently, there are three different electrolyser technologies — alkaline, proton exchange membrane (PEM), or solid oxide — each with varying efficiencies, capital costs, and operational characteristics, that can be coupled with floating or fixed-bottom wind turbines.

Hydrogen produced offshore could then be either transported via pipelines or stored on-site using compressed gas or liquid hydrogen technologies, and potentially converted into chemical carriers like ammonia for efficient shipping to shore. The choice of technology and system architecture will depend on various factors, including site-specific conditions, energy resource availability, and the scale of production desired.

Hydrogen produced offshore taps into abundant renewable energy while avoiding land-use conflicts. It also creates jobs in remote coastal areas and enhances energy security by diversifying energy sources and reducing reliance on fossil fuels.

Despite the challenges confronting offshore green hydrogen developments, pioneering companies are pushing ahead with their own projects.

In Scotland, for example, some of the winners in the record-sized ScotWind floating wind round have made hydrogen production a key part of their plans.

In Germany, the AquaVentus project seeks to establish a large-scale offshore hydrogen production facility powered by dedicated North Sea wind farms, with a targeted production capacity of 10GW of green hydrogen by 2035.

This is a huge undertaking bringing together a diverse range of stakeholders, including energy companies, technology providers, research institutions, and government agencies.

Offshore hydrogen production can follow two distinct strategies: turbine-level electrolysers or centralised platform-based systems. Another all-encompassing strategy includes energy islands.

Single turbine-level electrolysers

From a positive standpoint this approach not only reduces power transmission losses by converting electricity to hydrogen at source, but it allows modular and scalable rollouts while lowering curtailment risk for individual turbines. Despite these promises, there is high Capex due to duplication of systems (electrolyser, desalination, compression). Also, maintenance will become complex due to distributed locations, especially in harsh offshore environments. Furthermore, safety and access challenges increase with scale and turbine distance.

The economic challenge of the turbine-level electrolyser strategy is that Opex will increase dramatically due to access and servicing costs. Economies of scale are limited, and asset redundancy is hard to justify unless paired with local offtake or niche applications (e.g. fueling offshore O&M vessels).

Platform-based production: Centralised electrolysis for wind farms

Contrary to the single turbine-level electrolyser approach, platform-based production enables economies of scale in electrolyser size, desalination, compression, and storage. It also simplifies operations and reduces maintenance redundancy and is well suited for the integration of additional functions such as battery buffering or thermal integration.

High platform Capex also can be expected from this route, and it will require complex engineering for large installations. With the renewable energy sector facing a significant skills shortage, curtailing rapid growth and deployment, this may be a major issue.

The exporting of hydrogen requires additional infrastructure (subsea pipelines or liquefaction), and it may be vulnerable to single-point failures without redundancy.

From an economic perspective, this approach does offer a better levelised cost of hydrogen due to scale efficiencies.

However, its cost competitiveness will depend heavily on the export route: gaseous pipeline vs. ammonia conversion vs. liquid organic hydrogen carriers (LOHC). There is also consideration that LOHC adds trade-offs in purity, efficiency, and market compatibility.

Energy islands or hydrogen hubs

Plans for the establishment of energy islands are already underway across Europe. These islands are expected to maximise integration across multiple wind farms, electrolysers, storage, conversion, and interconnectors. They could facilitate hybrid models (electricity and hydrogen exports) and serve as transnational green energy hubs for broader regional cooperation, for example North Sea countries and Gulf states.

There is also potential for hybrid models that would utilise surplus energy from offshore wind and waste heat from other sectors, like nuclear or waste-to-energy, to improve electrolyser efficiency or for thermally-assisted synthesis to facilitate the production of ammonia for export.

This delay could also be due to a lack of governance, different jurisdictions, and market coordination complexity, especially if cross-border.

"Regulatory hurdles can slow down projects, complicate decision-making, and raise concerns about standards for safety."

There are significant regulatory and legal challenges when it comes to building energy islands, including securing the necessary permits, navigating international maritime laws, and aligning with national and EU energy policies.

Energy islands also can heighten geopolitical risk if not embedded in secure offtake frameworks. They are often located in contested maritime areas or near national borders. This could lead to disputes over ownership, rights to resources, and control of the infrastructure. In some regions, the construction of energy islands could provoke tensions between neighbouring countries, especially in the context of energy independence and security.

Considering the pros and cons of the three conceptual approaches to offshore green hydrogen, first and foremost developers should consider four key points:

Storage and offtake dilemmas

While hydrogen’s potential as a clean energy vector is immense, it comes with formidable challenges, particularly for developers who go down the aforementioned routes. The key dilemma for developers is whether to store the hydrogen offshore (risk, volume, and tech immaturity) or export it immediately via pipeline or carrier (infrastructure-heavy, costly).

The highly flammable nature of hydrogen requires robust safety procedures for storage and handling throughout the offshore production process, adding complexity and cost. It also comes with specialised infrastructure needs; offshore hydrogen production requires specialist storage facilities. The unique properties of hydrogen, particularly its low density, necessitate expensive high-pressure or cryogenic (extremely cold) storage solutions.

Developers can export hydrogen immediately via pipeline or carrier, but this infrastructure is costly.

When considering hydrogen export, it is important to consider how far the hydrogen will need to be transported. When transporting liquid hydrogen on ships, there is a substantial amount of energy needed to keep the hydrogen in cryogenic conditions. Because of the transportation challenges, it may be more efficient to produce hydrogen closer to where it will be used, such as refineries or other industrial sites.

Furthermore, ammonia or LOHC conversion for shipping adds Capex, energy penalty, and reconversion costs.

Given all these considerations, offtake agreements are critical for financing. Here, governments can play a key role through contracts for difference public procurement mandates, or blending mandates (e.g. in pipelines or shipping fuel).

Offshore a significant opportunity

Despite the headwinds, hydrogen represents a significant opportunity in the transition to cleaner energy systems.

Collaborative efforts between private industry, governments and research institutions can overcome barriers and help offshore green hydrogen achieve its potential as a cornerstone of a low-carbon future. This can be achieved through continued support for infrastructure development and certification processes.

Maximising these opportunities will require continued advancements in electrolysis technology, particularly those that enhance efficiency, durability, and scalability leading to a reduction in production costs and improvement in performance.

Similarly, advancements in hydrogen storage technologies, which can enable the safe and cost-effective storage of hydrogen both offshore and onshore, will be vital for integrating offshore production into the wider energy system.

This article is also published on RECHARGE News. illuminem Voices is a democratic space presenting the thoughts and opinions of leading Sustainability & Energy writers, their opinions do not necessarily represent those of illuminem.