Turning the North Sea into a world first green power plant

Working with a consortium of transmission system operators, we’re designing a new concept for hydrogen production integrated with electrical power export to the onshore grid. This uses cutting edge hydrogen production technology to support energy recovery from offshore wind on an unprecedented scale across north-west Europe.

The North Sea Wind Power Hub (NSWPH) consortium is developing big plans to realise the North Sea’s green energy potential by combining offshore wind with hydrogen production and supply clean energy − initially into existing markets in the Netherlands, Germany and Denmark, with potential to expand into Belgium, Norway and the UK.

Our work over three phases required extensive supplier engagement to gain the most complete understanding of the market and to look ahead to 2030 to predict how technological advancements might affect the project.

The first phase involved six months of techno-economic comparative evaluation of onshore versus offshore, platform-based hydrogen production – all with grid connections. At first glance onshore production with grid connections may seem easier, but this is not necessarily the case when availability of land, permitting requirements, the impact on local communities and the cost of bringing electricity ashore from distant offshore wind farms are taken into consideration.

The selection of onshore or offshore production considers electricity and hydrogen demand profiles through the energy transition up to 2050, the ultimate cost of electricity and hydrogen production and the flexibility in energy generation that can be achieved.

“At the scale of hydrogen production considered, you can have hydrogen production either on a major onshore facility or installed on the largest offshore platforms currently constructable,” says our project manager Jamie Paul.

Taking hydrogen production to a grand new scale

Working closely with NSWPH was crucial in such a ground-breaking project. “Regular deep dive sessions allowed the team to consider each of the key design decisions efficiently, reaching a consensus on the way ahead,” says Jamie. This included exploration of electrolyser technologies, types of cooling system, platform design and water resources and treatment.

Traditionally hydrogen has been created from natural gas using steam methane reformation. Natural gas is run through a reforming cycle, which consists of a catalyst bed where hydrocarbon (CH4) is cracked into hydrogen and carbon dioxide. By contrast, low-carbon or green hydrogen is generated through electrolysis of water using renewable electricity to separate the hydrogen from oxygen. Currently available technologies include the proton electrolyte membrane (PEM) or alkaline electrolysers.

“One issue is that commercially available hydrogen equipment is of the several megawatt scale. We are looking at gigawatt scales,” says Jamie. This meant creating a team of process experts focused on hydrogen to push the boundaries of current design. From the requirement for hundreds of offshore wind turbines, each equivalent to the height of the Eiffel Tower, to the use of electrolyser modules containing more stacks and cells than ever before in an offshore environment, the project is exploring hydrogen production at a grand new scale.

Electrical equipment challenge

The electrical equipment needs for the project posed a similar challenge. The team needed to scale up components such as transformers and rectifiers and determine how best to integrate them with the electrolysis equipment.

Building on the comparative analysis of onshore and platform-based hydrogen production, the second phase of the project compared offshore hydrogen production platforms with an alternative option of a single, large offshore installation built on an artificial caisson island. The island would support the full offshore hydrogen generation capacity as well as the high voltage electrical equipment required to transmit electricity to shore.

Platforms are expensive to build and therefore tend to be designed to incorporate the smallest and lightest possible equipment. A caisson island can accommodate equipment on a scale more akin to an onshore facility. The use of a caisson for hydrogen production could represent a middle ground between offshore platform and onshore concepts, but also introduces new challenges that can be circumvented with the platform solution.

Modelling the costs

The development of our in-house economic model is key to the assessment of each of the hydrogen production concepts. Integrating with the outputs of the design team and based on a generated power generation profile governed by the wind profile, the model can produce the levelised cost of hydrogen and electricity over the full project lifetime. A key feature is that it allows the assessment of any sensitivities, so that the design can be optimised. It considers the impact of alterations to the project parameters and evaluates the impact of changes in onshore power supply and demand.

“Our technical team built up the costs at a component-by-component level,” says chief economist Guy Doyle. “I take those figures and I turn it into cash flows in a discounted cash flow analysis.”

The model is iterative, so that as new data is gathered, or designs change, it can be rerun for different scenarios or to test the impact of different equipment or technology selections. It could also be extended to consider an even wider context.

Safety first

As green hydrogen production develops in scale and complexity, understanding any safety impacts associated with hydrogen will remain a critical component of design development. Our team of safety experts combined experience from the oil and gas and nuclear industries to identify the risks and impacts of managing hydrogen, building this into the development of the hydrogen production system design.

“Generally, safety cases for offshore installations are based on oil and natural gas experience,” explains process safety engineer Steven Melens. The starting point therefore was an analysis of the differing properties of the gases and their risks.

Mechanical equipment would need to be designed with emergency procedures such as venting or flaring of gas in mind. “We were looking rigorously at scenarios of venting hydrogen in an emergency, and painstakingly at how hydrogen can leak from high-pressure and low-pressure equipment,” says Steven. For this we used industry-standard consequence analysis software called PHAST. It was vital to consider whether an emergency would create a domino effect on surrounding infrastructure and whether there could be any risk to human safety.

Drawing on data from the European Hydrogen Incidents and Accidents database (HIAD 2.0) collated by the EU Commission Joint Research Centre in the Netherlands, and comparable systems in other sectors, we specified ideal stack heights for proposed safety vents and developed design recommendations for separation distances between the hydrogen stacks and oxygen stacks, as well as other co-located equipment. Firewalls would be needed to prevent the effects of thermal radiation on other infrastructure located on the island.

This work also enabled the client to understand what safety information would need to be obtained from the electrolyser manufacturers.

Hydrogen straight from the turbine?

Work is under way on the third phase of the project, which considers a more novel approach. Rather than having a centralised location to produce hydrogen − whether a series of offshore platforms as in phase one, or a single caisson island as in phase two − phase three would see wind power generation and hydrogen production combined at the turbine. This is being considered both with and without a grid connection.

In theory this allows a smooth switch between using wind energy for hydrogen production or for electricity export. Our design considers the technological challenges associated with this integration as well as the benefits in overall cost and the flexibility to increase total energy export. Greater flexibility offers the potential to increase the total energy export across the hydrogen production profile throughout the project’s lifetime, increasing overall revenues.

New frontier: Subsea hydrogen flowlines

An integral component of bringing the hydrogen generated at the wind turbines ashore are subsea hydrogen flowlines. Hydrogen flowlines have never been designed into offshore wind farms before.

Senior mechanical engineer Martyn Campbell has a decade of experience working in subsea pipeline and cable engineering and is relishing the challenge. “I’m working on the solutions to link all of these turbines using flexible flowlines and determining what sizes we need, what kind of materials are required, and how we are going to install it, potentially alongside array cables,” he says.

Thermoplastic composite flexible flowlines are preferred because of the dynamic environment and the favourable installation methods, which are similar as those for offshore cables. Martyn says the properties of a clean flow of hydrogen allow for a reasonably simple composite structure. Rather than the more complex multi-layer flexible pipeline structures typically used for hydrocarbons, a four-layer system can be used: “You’ve got the liner, a laminate layer, a coating and then an optional weight coating,” he explains.

Hydrogen would be collected by flexible flowlines linking the wind turbines, cumulatively gathering the gas until reaching a central compression platform where supply from all the wind turbines would converge. From here the hydrogen would be exported to shore by a much larger, rigid steel pipe installed on the seabed.

Transforming the future of energy

Findings from all three phases of the project will be used by NSWPH to assess and compare concepts for development.

The results of the project will be publicly available so that they will not only guide governmental policy decision making but provide a guide to sector developments for other stakeholders. It is hard to overstate neither the challenges of this project − which is pushing the boundaries of technological development − nor the enthusiasm with which the team has approached its work to build a legacy in clean and safe offshore energy.

As Jamie says: “This is a global-scale project that could potentially make a material difference as Europe completes its energy transition to net-zero.”