When the UK launched its long-awaited hydrogen strategy in 2021, the government made it clear that blue and green hydrogen were central elements in the race to net-zero. However, the on-land green hydrogen industry was faced with a tough question: how do we scale?
Despite the perception that the UK is water-rich, with large lochs and catchments present in the northwest and Scotland, the country’s usable and reliably available freshwater is in deficit. Beyond the strong running water supply required, onshore hydrogen production relies on dedicated wind and solar farms to conduct electrolysis or electricity from an already-congested power grid.
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These onshore hydrogen production challenges are leading companies to explore offshore methods of production. However, offshoring brings about an entirely new set of challenges that will affect the design of these new hydrogen production plants and the engineering decisions for seawater electrolysis. Identifying the trade-offs and advantages of each design will be crucial to ensure the right technology is being used at the right place and time, before making capital investments.
New avenues to meet global hydrogen targets
Global demand for hydrogen is projected to grow significantly over the coming decades, and governments from the EU to Japan are committing to industrial-scale targets to ensure this demand can be met. The UK is no exception, with Scotland alone targeting 25 GW of hydrogen production capacity by 2045, requiring a minimum of 28.5 billion litres of pure H2O a year to meet this target.
Achieving this level of hydrogen production requires significant freshwater resources, which the UK currently lacks. Scotland, for example, has more than 31,000 freshwater lochs and rainfall recorded over 250 days a year in some areas. However, Scottish Water reports a running freshwater deficit of 60 million litres per day, a figure that could reach 240 million litres per day by 2050.
Given freshwater deficits onshore, producing hydrogen offshore to meet this demand is becoming an attractive option. By relocating production to the sea, companies can utilise the electricity supplied by offshore wind farms, bypassing the limitations of onshore hydrogen infrastructure. This approach also involves placing electrolysers at sea and using seawater as feedstock rather than transporting freshwater to coastal sites. However, because electrolysis requires purified freshwater, the process must include offshore desalination. This is needed as seawater contains contaminants such as magnesium, calcium, chloride and microorganisms that reduce hydrogen production efficiency and accelerate electrode corrosion.
Offshore electrolysis draws on decades of experience from the oil and gas sector and onshore hydrogen projects, and the introduction of the first offshore hydrogen pilot plant built in the North Sea demonstrates the government’s support for this new infrastructure. But hydrogen production challenges do not simply disappear when operations move offshore. The combination of a hostile marine environment, renewable power variability, and seawater feedstock introduces a new set of complexities that existing onshore technologies do not yet fully address. The electrolyser choice in offshore hydrogen production illustrates this well: proton exchange membrane (PEM) technologies are mature and well-suited to adapt to the variable electricity output of offshore wind; however, they require ultrapure feedwater, which is not available offshore. Alkaline electrolysers tolerate lower feedwater quality, thus could be utilised with seawater, but introduce problems with chlorine evolution. Beyond the electrolyser, every component choice carries its own logistical, technological, and economic consequences. The challenge is therefore identifying the decisions and trade-offs that shape the balance of plant for each site.
Innovative framework to offshore hydrogen production
A collaborative project with the University of Edinburgh, Aqualution and Cairn Risk Consulting aims to identify the key factors involved in offshoring early enough to inform design, before capital commitments are made. This project is supportedby the Royal Commission of 1851 through its industrial fellowship programme, which recognises the value of empirical, decision-relevant data in supporting emerging industries. The University of Edinburgh will host lab experiments while Aqualution’s electrolyser technology will be repurposed for hydrogen production upon the Scottish Government’s request to meet the 2045 nation’s 25GW hydrogen target. This electrolyser technology was originally developed to produce highly stable hypochlorous acid — a pH-neutral disinfectant used in medical, agricultural and food processing applications — from salt, water and electricity.
Wan in the lab – University of Edinburgh
The first step of the project was to create data on how hydrogen production efficiency varies across the water purity spectrum, using a real electrolyser system rather than theoretical assumptions. The next stage of this research will use the experimental results and generated data to develop an expanded techno-economic framework to assess Aqualution’s hydrogen technology. This includes environmental and safety considerations as core dimensions. The wind industry’s struggle with blade disposal is a recent reminder of what happens when those dimensions arrive late.
Offshore hydrogen presents its own version of that risk when it comes to introducing large-scale alkaline chemistry into a formidable marine environment, which demands the same rigour as the economics. The framework will evaluate the full balance of plant configurations using development constraints such as energy availability and target hydrogen purity. Expert judgements will be incorporated to reflect the competing priorities in real-world engineering design decisions. It will also be designed to allow other original equipment manufacturers (OEMs) to run their own technology through the same assessment, benchmarking their performance within the broader context of an offshore installation.
The UK-Germany Hydrogen Corridor AquaDuctus offshore pipeline project, as well as a growing number of international developments, point to a future where offshore hydrogen is not only a North Sea story but a global one. The framework is not geographically constrained, nor is the challenge of freshwater access. North African countries have been identified as viable hydrogen producers for the EU using their considerable solar capacity, yet many face freshwater scarcity far more acute than Scotland’s.
Offshore green hydrogen is still a decade from industrial deployment at scale, but the questions being asked now will determine whether it arrives as a competitive option. This research will provide a structured, data-driven and expert-informed basis for the design decisions required to ensure the world can meet the ambitious targets it faces.
