Hereon: Offshore hydrogen production affects the North Sea

Offshore green hydrogen production in the German Bight may affect the North Sea’s marine environment, according to a new study by German research institute Helmholtz-Zentrum Hereon that highlights how waste heat from electrolysis could alter local water temperatures and sea stratification.

It is understood that almost 80% of the energy used worldwide currently comes from fossil fuels such as oil, coal, and gas, and 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) is said to lay the foundation for producing hydrogen using wind energy in the North Sea in the future. As informed, the goal is to install offshore hydrogen plants with a capacity of 10 gigawatts (GW) in offshore wind farms in the German Bight. According to Hereon, the technologies are currently being tested, with the focus so far primarily on technical feasibility and economic viability. The impact on the environment has only been considered to a limited extent, Hereon claimed, noting that its new 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.”

In offshore hydrogen production, seawater is reportedly first desalinated and then split into hydrogen and oxygen through a process called electrolysis. This is said to produce waste heat and brine. In the Hereon study, authors modeled a thermal desalination process based on evaporation and found that compared to brine, waste heat has a “significantly greater” impact on seawater. As reported, it causes the water temperature within a 10-meter radius around a 500-megawatt (MW) hydrogen plant to rise by up to 2℃ 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 GW and found that even within a radius of 1,000 meters, there was still an average annual temperature increase of 0.1 to 0.2℃. At a distance of 50 kilometers, it was still 0.01℃, Hereon stressed.

Lead Author Nils Christiansen from the Hereon Institute of Coastal Systems – Analysis and Modeling, stated: “The decisive temperature changes occur mainly locally and, depending on the scale of production, have an impact on the stratification of the water body.”

To note, 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, while the warmer, lighter water with a lower salinity is located above, Hereon explained, adding that the warmer layer acts as a barrier and influences the transport of nutrients from the bottom to the top. The Hereon study claims that the stratification intensifies when the water temperature at the surface rises due to the input of waste heat. Reportedly, this can alter nutrient transport and thus also the productivity of phytoplankton, which is found near the surface and is said to form the basis for the entire food chain in the sea.

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 electrolyzers producing hydrogen at different locations instead of one large electrolyzer on a single platform, Hereon said, stressing that 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.”

Christiansen concluded: “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. Further studies are now needed to investigate other technologies, such as chemical processes, and the exact impact on ecosystems.”