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Hereon study examines the effects of hydrogen production using offshore wind energy for the first time and offers environmentally friendly options for action
Green hydrogen is a key part of the energy transition. In the coming years, it'll be made in wind farms in the German Bight. With recent technology, this process creates waste heat and brine, which are both dumped into the sea. A new study by Helmholtz-Zentrum Hereon shows for the first time that the waste heat of 500-megawatt plant can increase the water temperature locally by up to 2 degrees Celsius, thereby influencing the stratification of the sea. The authors provide groundbreaking recommendations for the environmentally friendly expansion of the planned offshore hydrogen production in the North Sea. The study was recently published in the Nature journal npj Ocean Sustainability.
Almost 80 percent of the energy used worldwide currently comes from fossil fuels such as oil, coal, and gas. As part of the energy transition, these are to be increasingly replaced by environmentally friendly energy sources such as climate-neutral hydrogen. The German Offshore Wind Energy Act (WindSeeG) lays the foundation for producing hydrogen using wind energy in the North Sea in the future. The goal is to install offshore hydrogen plants with a capacity of 10 gigawatts in offshore wind farms in the German Bight. The technologies are currently being tested. Until now, the focus has been primarily on questions of technical feasibility and economic viability. The impact on the environment has only been considered to a limited extent. Using a computer model developed in-house, the new Hereon study analyzes for the first time the potential footprint of offshore hydrogen production in the North Sea and shows how the planned expansion can be achieved in an environmentally friendly manner.
Local temperature increase of 2 degrees Celsius
In offshore hydrogen production, seawater is first desalinated and then split into hydrogen and oxygen through a process called electrolysis. This produces waste heat and brine. According to the current state of technology, both are returned to the sea near the surface. The authors of the Hereon study based their calculations on a thermal process in which the water is desalinated through evaporation. The results of their modeling show that, compared to brine, waste heat has a significantly greater impact on seawater. It causes the water temperature within a 10-meter radius around a 500-megawatt hydrogen plant to rise by up to 2 degrees Celsius on average over the course of a year. The researchers expanded the scenario and calculated the impact for several hydrogen plants located close to each other with a total capacity of 10 megawatts. Even within a radius of 1,000 meters, there was still an average annual temperature increase of 0.1 to 0.2 degrees Celsius. At a distance of 50 kilometers, it was still 0.01 degrees Celsius.
“The decisive temperature changes occur mainly locally and, depending on the scale of production, have an impact on the stratification of the water body,” says lead author Dr. Nils Christiansen from the Hereon Institute of Coastal Systems – Analysis and Modeling. Stratification is the vertical division of the ocean into different water layers with varying density, temperature, and salinity. Colder, denser water with a higher salinity and many nutrients is found at the bottom. Above this is warmer, lighter water with a lower salinity. The warmer layer acts as a barrier and also influences the transport of nutrients from the bottom to the top. The findings of the Hereon study show that this stratification intensifies when the water temperature at the surface rises due to the input of waste heat. This can alter nutrient transport and thus also the productivity of phytoplankton. Phytoplankton is found near the surface and forms the basis for the entire food chain in the sea. In order to reproduce and carry out photosynthesis, it needs nutrients from the deeper layers.
Solutions for environmentally friendly hydrogen production
To minimize the impact of hydrogen production on stratification, the authors of the Hereon study recommend distributing the input of by-products spatially, for example through decentralized solutions. This involves several small electrolysers producing hydrogen at different locations instead of one large electrolyser on a single platform. It also makes sense to distribute the input across the water column, from near the surface to the seabed, or to reduce waste heat through technological solutions. “Our findings help to better understand the impact of green hydrogen production on the oceans and to develop solutions for a sustainable and nature-friendly energy transition at sea at an early stage,” says Nils Christiansen. “Further studies are now needed to investigate other technologies, such as chemical processes, and the exact impact on ecosystems.”
Cutting-edge research for a changing world
Helmholtz-Zentrum Hereon's scientific research aims at preserving a world worth living in. To this end, around 1000 employees generate knowledge and research new technologies for greater resilience and sustainability - for the benefit of the climate, the coast and people. The path from idea to innovation leads through a continuous interplay between experimental studies, modeling and AI to digital twins that map the diverse parameters of climate and coast or human biology in the computer. This is an interdisciplinary approach that spans from the fundamental scientific understanding of complex systems to scenarios and practical applications. As an active member of national and international research networks and the Helmholtz Association, Hereon supports politics, business and society in shaping a sustainable future by transferring the expertise it has gained.
Hydrogen research at Hereon
Several departments at Hereon are dedicated to the research of green hydrogen. At the Institute of Hydrogen Technologies, scientists are developing metal hydrides for the efficient storage of hydrogen and investigating the use of heat in this context. At the Institute of Functional Materials for Sustainability at Hereon's campus in Teltow, researchers are developing the “artificial leaf” that produces green hydrogen based on natural processes.
Dr Nils Christiansen
Scientist
Institute of Coastal Systems - Analysis and Modeling
Tel: +49 (0) 4152 87-2132
Mail: nils.christiansen@hereon.de
Offshore hydrogen production leaves a local hydrographic footprint on stratification in the North Sea
https://statics.teams.cdn.office.net/evergreen-assets/safelinks/1/atp-safelinks....
http://Institute for Coastal Systems - Analysis and Modeling
https://www.hereon.de/institutes/coastal_systems_analysis_modeling/index.php.en
http://Hereon press release: Award for Hereon researcher Nils Christiansen
https://www.hereon.de/institutes/hydrogen_technology/news/116052/index.php.en
Simulations of possible production platforms for offshore hydrogen. Centralized production on a sing ...
Aquaventus Förderverein e.V.
Aquaventus Förderverein e.V.
CORRECTION!
In the press release “Offshore hydrogen production affects the North Sea” dated Tuesday, June 10, 2025, 10:32 a.m., we made an error in the third paragraph, seventh sentence. Instead of “10 megawatts,” it should be “10 gigawatts.”
The correct sentence reads as follows:
The researchers expanded the scenario and calculated the impact for several hydrogen plants located close to each other with a total capacity of 10 gigawatts.
We apologize for this error. Please include this correction in your reporting.
The full press release and the original publication of the study can be found on the website of the Helmholtz-Zentrum Hereon:
https://hereon.de/communication_media/news/118110/index.php.en
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Simulations of possible production platforms for offshore hydrogen. Centralized production on a sing ...
Aquaventus Förderverein e.V.
Aquaventus Förderverein e.V.
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