Green hydrogen pilot will test offshore electrolysis

Most of the offshore windfarms in the Netherlands have been built close to the shore but in the longer term there are plans to build vastly more capacity far from shore.

The transmission costs associated with bringing many gigawatts of electricity ashore from windfarms far offshore – some in excess of 100 km from land – are significant, but another solution exists that could be less expensive.

That solution would also enable existing oil and gas infrastructure to be re-used, and power from offshore wind to be brought ashore not as electrons, but as molecules, in the form of renewable of ‘green’ hydrogen, as TNO energy expert Dr Rene Peters told OWJ.

In fact, Dr Peters and colleagues in the PosHYdon project believe ‘old energy’ infrastructure could play a key role bringing clean energy ashore if platforms and pipelines currently used by the Dutch offshore oil and gas industry could be repurposed. Many such platforms are becoming obsolete as reservoirs are depleted. Legislation dictates that the platforms should be dismantled – which is expensive – so alternatives to dismantling would be welcome.

The green hydrogen would be produced by electrolysers installed on the oil and gas platforms, blended with natural gas and pumped ashore. The power to electrolyse water to produce hydrogen would come from far-from-shore windfarms, and the PosHYdon pilot project will provide a way to test whether the idea works.

“We know that connecting more and more offshore wind to the grid is potentially problematic,” said Dr Peters. “If you go far offshore, you need high voltage DC transmission, which is expensive.

“At the moment, there is not enough grid capacity and the grid on land also needs upgrading. When you look at windfarms that are 100 km or more from shore, it makes more sense to bring the power ashore using another energy carrier such as hydrogen. The feasibility of doing so, and reducing transmission costs for energy from offshore wind, is what we are going to test in PosHYdon.”

Apart from the fact a lot of Dutch offshore oil and gas platforms are reaching the end of their useful lives and either need to be decommissioned or re-used, the plan is also a good fit with growing recognition of the role that green hydrogen will play in decarbonisation and its potential use in industry and other parts of the economy.

Using electrolysers to produce hydrogen on land is a mature technology that is well understood, but it has never been done in the offshore environment. Hence the need for the PosHYdon project, which originated at Nexstep, the Dutch association for decommissioning and reuse, and TNO.

“In the PosHYdon pilot project, we have brought together oil and gas operators, Gasunie, which manages and maintains infrastructure used to transport and store gases in the Netherlands and other industry leaders to see whether it can be done offshore,” Dr Peters explained.

“The offshore platform that has been selected to test the idea, Neptune Energy’s Q13a, is the first fully electrified platform in the Dutch sector of the North Sea. Although it is close to the shore, and not representative of the far-offshore platforms where green hydrogen may one day be produced, it is ideal for the pilot because it has sufficient spare electrical power to operate the electrolyser stack we will install.

“It is an oil platform, but it also handles associated gas. The green hydrogen produced by the electrolysers installed on the platform will be injected into the gas stream from Q13a and sent ashore.”

Marinising the electrolyser stack for use in the offshore environment should be relatively straightforward. What is more interesting and potentially challenging to the project partners is seeing how the electrolysers handle the dynamic load from an offshore windfarm.

For the purposes of the project, the fluctuating load from Eneco’s Luchterduinen offshore windfarm will be simulated, rather than adding to the cost of the pilot project by actually connecting cables from it to the Q13a. That fluctuating load might represent a challenge for some electrolysers but not others.

“Some electrolysers are better than others at handling dynamic loads,” said Dr Peters. “That some of them can do so is clear from solar-powered green hydrogen projects that handle very high loads during the day and none at night.”

For the purposes of PosHYdon, the project partners have opted to use proton exchange membrane (PEM) electrolysers that exhibit fast response when operating dynamically, as when powered by renewable energy such as solar and wind.

Apart from testing the ability of PEM electrolysers to work in an offshore environment and handle dynamic loads, the PosHYdon pilot will also address some of the important safety and regulatory issues around producing hydrogen on an offshore platform. “These include that oxygen is also produced with electrolysis,” Dr Peters explained.

“There is no economic value in that oxygen, but it does need to be dealt with, safely, in an oil and gas environment, when there are hydrocarbons involved and equipment associated with hydrocarbons such as pumps and compressors. We are working with the authorities and the regulators to address these challenges – it is a learning project,” Dr Peters said.

Asked about potential commercial-scale projects and what level of capacity could be installed on a re-used offshore platform such as Q13a, Dr Peters said he anticipated the maximum green hydrogen capacity from an installation of that size would be approximately 250-300 MW. Greater capacity, in the order of 400 MW, would require larger platforms to be used.