Effects of Floating Solar Platforms on the Hydrodynamics and the Ecosystem of a Coastal Sea

Abstract

The effects of floating photovoltaic (PV) installations on the hydrodynamics and the ecodynamics of a coastal sea as the North Sea are analysed, with a coupled physical-biogeochemical 1D column model (GOTM-ERSEM-BFM). The model is calibrated and validated with the use of Smartbuoy observations from three locations in the North Sea. The equations of the model are altered as to include four different effects (ef) of the PV installations, namely: ef1) decreased light conditions due to the shadowing effect of the platforms, ef2) reduced wind stress due to the limitation of the free surface of the water column, ef3) introduction of an additional surface stress experienced by currents, due to friction induced by the platforms, ef4) reduced wave height due to the presence of the platforms. The 1D model is capable of reproducing the main seasonal patterns of ecosystem variables such as chlorophyll a, with performance comparable to a 3D model. Moreover, it proves to be more efficient in open-sea locations where horizontal advection is of less importance. Regarding the individual effects, ef1 is the dominant one. However, some ecosystems may reveal resilience to ef1 for small percentages of coverage. The effect of ef2 on the hydrodynamics and the ecosystem is small in locations with strong tidal currents. This effect can be very important for stratified locations due to its impact on the top mixed layer and thus on primary production. The ef3 can be important for the ecosystem of locations with strong currents. This is evident for small percentages of coverage where ef3 leads to a minimum of suspended sediment near the surface (and maximum of irradiance). The ef4 reduces strongly the concentration of suspended sediment in the water column. However, the reduction occurs mainly at lower depths and out of the photic zone, leading to no significant changes in the light availability of the ecosystem. Overall, the shadowing effect (ef1) of the platforms on the ecosystem is the most important. However, for the case of well mixed locations with high concentration of suspended sediment near the surface, ef1 is partly compensated by the effect of reduced turbidity that follows the other three effects. This is more prominent for small percentages of coverage where ef3 is of comparable importance to ef1, resulting in no significant overall impact of the PV installations on the marine ecosystem. Concluding, well mixed locations with high currents and large concentration of suspended sediment near the surface are more favorable to the installation of a solar power plant. However, this statement is restricted by the assumption that the power plant will not occupy more than 20% of the 1D domain.