Model tests in shallow water basin

To validate the numerical simulations, MARIN performed model tests in its shallow water basin. The scale model is equipped with glass fibre optical bending sensors to validate the predicted beam bending. In addition, the relative wave motions and floater motions were measured during the tests. We expect to publish the results of the validation work in a conference paper in 2026.

Structural flexibility

MARIN’s scope in this project addresses the station keeping and seakeeping behaviour of this concept, with the main focus on girder stress and airgap. Both aspects are influenced by the structural flexibility of the girders. Therefore, an Euler-Bernoulli beam model has been implemented in the XMF time domain framework. Implementing FEM types of modelling techniques in XMF resulted in a fast and reliable tool to assess the girder stress and airgap in a variety of sea states. The computational efficiency of the tool was such that a wide variety of OFPV designs could be analysed. The Euler-Bernoulli beam model in XMF is now available for all new projects under the name “Bendy”, referring to “bending dynamics”.

The lily’s structure of radial and tangential girders will be researched and engineered using flexible, eco-friendly Ultra High-Performance Concrete. The concrete girders support a lightweight sheet, which spans the construction like an umbrella, providing sufficient carrying capacity for the PV panels, as well as maintenance technicians.

Water lily inspiration

This sheet will have openings to ensure sufficient sunlight reaches the water surface and will also serve to minimise the risk of uplift and buckling by the wind. To reduce the effect of the waves, the concrete web will be raised well above the water by small diameter floating columns. Elevating the construction above the water surface will prevent wave overtopping and reduces the overall wave excitation and formation of fouling on the PV panels. The conceptual picture of the design is shown in figure 1.

Airgap challenge

In the conceptual design phase, the main challenge addressed was airgap. The solar deck, and particularly the PV modules, are vulnerable to green water. There is no allowance for waves exceeding the solar deck. Initially, the design strategy was to let the platform move up and down with the waves, and to provide sufficient flexibility to allow the structure to bend or curve over the wave crest. This desired behaviour however requires an extremely lightweight structure, which was difficult to obtain in concrete. The inertia of the platform prevents it from moving with the waves. This effect can partially be compensated by more waterplane area (larger column diameter). Eventually, the design strategy was to raise the solar deck with a light truss structure to ensure a dry solar deck.

NaturSea-PV is a project within the Horizon Europe research and innovation programme addressing the need for a sustainable, reliable and competitive energy supply. A water lily-inspired Offshore Floating Photovoltaic (OFPV) solution will be developed.