Location of existing wind turbines in the Belgian part of the North Sea (AC), as well as the modeled layout (F) of combined wind turbine monopiles (D) and floating photovoltaic structures (E). Credit: Denis et al, 2025.
Floating solar installations offer a tantalizing vision of sustainable energy, combining wind and solar power in the same offshore space. But according to new research, the seabed could suffer the effects of such ingenuity.
In a Frontiers of Marine Science publication, a team of scientists examined how floating photovoltaic (FPV) structures, deployed in the Belgian part of the North Sea and combined with an offshore wind farm, change the hydrodynamics, in turn affecting currents, turbulence and seabed stress.
The North Sea is already a hotspot for offshore renewable energy, with the proliferation of wind farms and expansion ambitions ranging from currently providing around 25 gigawatts of electricity to 300 gigawatts by 2050.
To optimize the use of this marine real estate, the concept of placing FPV units above or around existing wind turbine areas is gaining ground: solar panels floating on pontoons or mounted on elevated frames can capture sunlight in sunnier, quieter areas while sharing grid connection infrastructure with the wind turbines.
The hope is a win-win: higher total production and more efficient use of offshore space. However, this study warns that even if electricity can flow, other physical consequences can ripple through the ecosystem.
PhD researcher Pauline Denis and her colleagues from the Royal Belgian Institute of Natural Sciences used a high-resolution three-dimensional hydrodynamic model (COHERENS) to simulate several scenarios in a 25 km area around the site of the “Mermaid” wind farm in the Belgian North Sea.
They compared a reference situation without structures to a scenario with only wind turbines and to two mixed cases with wind turbines and FPV, with sparse or dense solar coverage (corresponding to ~126 megawatts and ~252 megawatts of solar capacity, respectively).
They focused on four key hydrodynamic measurements: the amount of obscured sunlight (and how that affects sea surface temperature), changes in current speeds, changes in turbulent kinetic energy (a measure of the amount of turbulence in the water), and differences in bottom shear stress (the force the water exerts on the seafloor).
The shading effect was found to be modest. In summer, they found that installing dense FPVs cooled the sea surface by 0.006°C on average, reaching a maximum of 0.03°C in locations directly beneath the floating units.
In other words, the massive solar panels floating on top of the water did not substantially change the water temperature. This suggests that for this elevated design, shading may not be the greatest concern compared to other designs located directly on the sea surface (although the authors note that their model assumed total light blocking by the panels and did not take into account the heat given off by the panels themselves).
This also means that the effect on photosynthetic organisms in the upper layers of the water column and subsequent impacts on marine food chains may be less than previously thought.
On the other hand, the impacts on currents, turbulence and seabed shear stresses were more significant. Compared to the wind-only scenario, the addition of FPV reduced the average surface current speed in the dense configuration by up to 20.7%.
Floating solar panels not only slow surface currents, but also increase water turbulence, stirring up sediment and changing the way energy flows in the marine environment.
The impact on bottom currents was much less, with a difference of only about 0.5%, but this should not downplay the importance of what is happening on the sea floor. FPV structures introduce significantly more submerged surface area (such as floats, support frames and moorings) than conventional wind turbine foundations, perhaps up to 20 times more submerged surface area per megawatt of installed capacity compared to monopile wind turbines.
This is important because submerged structures act as obstacles to flow: they slow and redirect currents; generate turbulence; change the way sediments are moved, deposited or eroded; and finally affect the lower shear stress. In this case, the model revealed that in the dense FPV scenario, the bottom shear stress was changed locally by up to 63% compared to the wind-only configuration.
Even more striking, the area of the seabed where the bottom shear stress changed by more than a 10% threshold (a guideline used in Belgian monitoring of risks related to benthic habitats, or seabeds), extended up to 1.8 times the size of the wind farm site and more than 23 times the area covered by the FPV units themselves.
In short: the footprint of influence on the seabed was much greater than that of solar panels floating above the water. In fact, the doubling of photovoltaic capacity has more than tripled the area of the seabed affected.
Relative differences in bottom shear stresses in winter (a, b) and summer (c, d) resulting from the sparse and dense arrangement of FPVs along wind turbines, compared to wind turbines alone. Credit: Denis et al, 2025.
Why is this important? The seafloor supports benthic habitats and organisms, and the force with which water moves over sediment plays a central role in the transport, erosion, deposition, and resuspension of sediment. As shear stress increases, sediment can be eroded, so that particles re-enter the water column and change turbidity; as shear stress decreases, sediment can be deposited further, thereby changing the habitat.
Therefore, hydrodynamic changes induced by floating solar could alter the functioning of marine ecosystems by altering biogeochemical cycles, nutrient and carbon deposition, larval dispersal, and sedimentation patterns.
The researchers point out that while the impacts of offshore wind farms have been documented, floating solar remains much less studied. This work therefore highlights how the co-location of floating solar and wind energy deserves greater attention.
The team points out some reservations about its results: the modeling resolution (50 × 50 m grid) cannot resolve very small-scale processes (e.g., vortices swirling behind structures) and the model does not include the effects of waves, mooring systems, or biofouling (organisms growing on structures that would increase drag, such as mussels or barnacles).
They also lack in situ observational data for these processes in offshore conditions, meaning that the model results should be considered an early estimate and not a definitive measurement. Nevertheless, the work offers a pioneering assessment of the hydrodynamic impacts of high FPVs in an offshore wind farm context.
For policymakers, planners and renewable energy developers, the study sends a clear message: integrating floating solar into offshore wind farms may seem like an effective way to optimize marine space, but it is not without environmental costs. The magnitude of hydrodynamic influence on seafloor conditions and benthic ecosystems can be significant and extend well beyond the visible footprint of solar units.
As offshore renewable energy expands, the cumulative effects of multiple installations (wind, solar and wave) must be considered in marine spatial planning, environmental impact assessments and monitoring programs.
In the context of the public debate on marine renewable energy – where the emphasis is on cost-effectiveness, network integration, space use and reduction of carbon emissions – this study serves as a reminder that marine ecological and physical impacts must remain central. The energy transition will necessarily involve offshore engineering, but engineering and ecology must go hand in hand.
While floating solar can still make a valuable contribution to offshore renewables, designers would do well to consider hydrodynamic knock-on effects: designing configurations and densities that minimize flow disruptions, anchoring and mooring systems that limit seabed disturbance, and rigorous monitoring of sediment and benthic responses.
Ultimately, the next generation of floating solar-wind hybrids should not only ask how much energy we can produce, but also how they will reshape the seafloor environment.
Written for you by our author Hannah Bird, edited by Sadie Harley, and fact-checked and edited by Robert Egan, this article is the result of painstaking human work. We rely on readers like you to keep independent science journalism alive. If this reporting interests you, consider making a donation (especially monthly). You will get a without advertising account as a thank you.
More information:
Pauline Denis et al, Hydrodynamic alterations induced by floating solar structures co-located with an offshore wind farm, Frontiers of Marine Science (2025). DOI: 10.3389/fmars.2025.1674859.
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