Floating solar panels are stressing the seafloor

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 may be feeling the strain of such ingenuity.

In a Frontiers in Marine Science publication, a team of scientists examined how elevated floating photovoltaic (FPV) structures, deployed in the Belgian part of the North Sea and combined with an offshore wind farm, alter hydrodynamics, in turn affecting currents, turbulence, and seabed stress.

The North Sea is already a hotspot for offshore renewable energy, with wind farms proliferating and ambitions for expansion going from supplying approximately 25 gigawatts of power presently to 300 gigawatts by 2050.

To optimize use of this marine real estate, the concept of placing FPV units above or around existing wind turbine zones is gaining traction: solar panels floating on pontoons or mounted on elevated frames can tap sunlight in sunnier, calmer patches while sharing grid connection infrastructure with wind turbines.

The expectation is a win-win for higher total output and more efficient use of offshore space. However, this study cautions that while the electricity may flow, other physical consequences may ripple through the ecosystem.

Ph.D. researcher Pauline Denis and colleagues at the Royal Belgian Institute of Natural Sciences used a high-resolution three-dimensional hydrodynamic model (COHERENS) to simulate several scenarios in a 25km area around the “Mermaid” wind farm site in the Belgian North Sea.

They compared a baseline with no structures to a scenario with only wind turbines and two mixed cases with wind turbines plus FPVs, with either sparse or dense solar coverage (corresponding to ~126 megawatts and ~252 megawatts of solar capacity, respectively).

Their focus was on four key hydrodynamic metrics: how much sunlight was shaded out (and how that affected sea surface temperature), changes in current speeds, changes in turbulent kinetic energy (a measure of how much turbulence is in the water), and differences in bottom shear stress (the force the water exerts on the seabed).

The shading effect turned out to be modest. In summer, they found that the installation of dense FPV cooled the sea surface by an average 0.006°C, reaching a maximum of 0.03°C in spots directly beneath the floating units.

In other words, the massive solar arrays floating above the water didn’t substantially alter water temperature. That suggests that for this elevated design, shading may not be the biggest concern when compared to others sitting directly on the sea surface (though the authors note their model assumes full light blockage by the panels and did not consider heat released by the panels themselves).

It also means there could be less of an effect on photosynthesizing organisms in the upper layers of the water column and subsequent impacts on marine food chains than previously thought.

By contrast, the impacts on currents, turbulence, and seabed shear stress were more significant. Compared to the wind-only scenario, the addition of FPVs reduced average surface current speed in the dense setup by up to 20.7%.

The floating solar panels not only slow surface currents but also increase turbulence in the water, stirring up sediment and altering how energy flows through the marine environment.

The impact on bottom currents was much smaller, only about 0.5% difference—but this shouldn’t minimize the importance of what happens at the seabed. The FPV structures introduce many more submerged surfaces (such as floats, support frames and moorings) than typical wind turbine foundations, perhaps up to 20 times more submerged surface area per megawatt of installed capacity compared to wind monopiles.

This is significant because submerged structures act like obstacles to flow: they slow and redirect currents; generate turbulence; alter how sediment is moved, deposited, or eroded; and ultimately affect the bottom shear stress. In this case, the model revealed that in the dense FPV scenario, bottom shear stress was altered by up to 63% locally compared to the wind-only setup.

More strikingly, the area of seabed where bottom shear stress changed by more than a 10% threshold (a guideline used in Belgian monitoring of benthic, or seabed, habitat risk) extended to 1.8 times the size of the wind farm site, and more than 23 times the surface area covered by the FPV units themselves.

In short: the footprint of influence on the seabed was much larger than the solar panels floating above the water. In fact, doubling the photovoltaic capacity more than tripled the seabed area impacted.

Why does this matter? The seabed is home to benthic habitats and organisms, and the force with which water moves over sediments plays a central role in sediment transport, erosion, deposition, and resuspension. When the shear stress increases, sediments may be eroded so particles re-enter the water column and change turbidity; when shear stress decreases, sediments may settle more, altering habitat.

Therefore, the hydrodynamic shifts induced by floating solar might change how marine ecosystems function by altering biogeochemical cycles, nutrient and carbon deposition, larval dispersal, and sedimentation patterns.

The researchers emphasize that while offshore wind farm impacts have been documented, floating solar remains far less studied, so this work highlights how floating solar plus wind co-location deserves closer attention.

The team do point out some caveats to their findings: the modeling resolution (50 × 50 m grid) cannot resolve very fine-scale processes (for example, vortices swirling behind structures) and the model did not include the effects of waves, anchoring systems, or biofouling (organisms growing on structures which would increase drag, such as mussels or barnacles).

They also lack in-situ observational data for these processes in offshore conditions, meaning the model results must be seen as an early estimate, not a definitive measurement. Nonetheless, the work offers a pioneering assessment of the hydrodynamic impacts of elevated 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 an efficient way to maximize marine space, but it is not without environmental cost. The scale of hydrodynamic influence on seabed conditions and benthic ecosystems can be significant and extend well beyond the visible footprint of the solar units.

As offshore renewables expand, the cumulative effects of multiple installations (wind, solar and wave) need to be factored into marine spatial planning, environmental impact assessments, and monitoring programs.

In the context of the public debate over marine renewables—where much emphasis is placed on cost efficiencies, grid integration, space use, and carbon emission reduction—this study acts as a reminder that ecological and physical marine impacts must remain central. The energy transition will necessarily involve engineering at sea, but engineering and ecology must go hand in hand.

While floating solar may still offer a valuable contribution to offshore renewables, designers would be wise to factor in hydrodynamic ripple effects: designing layouts and densities that minimize flow disruption, 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 just ask how much energy we can generate, but also how they will reshape the seabed environment.

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