Dynamic power cable configuration for lightweight floating photovoltaic systems in the North Sea

Abstract

Floating photovoltaic (FPV) systems offer a way to expand solar power offshore and can potentially be integrated with existing wind farms to diversify energy mix. A key challenge is the design of the dynamic power cable (DPC) that transports electricity from floating units to the seabed while subjected to waves, currents, and wind. This thesis evaluates the structural behaviour and installation feasibility of DPCs for a lightweight FPV concept (Solar@Sea III developed by Bluewater Energy Services) in shallow North Sea conditions at 20 m and 35 m water depth.

In this study, time-domain finite-element simulations in OrcaFlex are used under Ultimate Limit State (ULS) conditions. Two configurations, catenary and lazy-wave, are compared. A parametric study varies hang-off point (HOP) angle, bend-stiffener dimensions, and buoyancy-section characteristics. Decoupled and coupled analyses then assess three integration points within the FPV system: the floater, a corner buoy, and the transverse line. Performance is measured by peak curvature, tension, and seabed clearance.

Curvature is the governing design constraint; tensions remain well below strength limits across cases. Standard bend stiffeners reduce end-region curvature but are not sufficient alone. Combined HOP-angle adjustments and stiffer or longer bend stiffeners are most effective in 20 m water depth. At 35 m, curvature hotspots move away from the ends, and benefits from local end-point adjustments decrease. Lazy-wave configurations increasingly help at 35 m by lowering curvature, distributing it along the cable’s length, and stabilising tensions. At 20 m, however, they provide limited seabed clearance (often <2 m), which is operationally risky without accurate buoyancy calibration and regular inspection.

System integration strongly influences performance. Among the tested connection points, the corner buoy offers the best balance of mechanical response and practicality, acting as an accessible hub that reduces motions at the HOP and eases installation and maintenance. For 20 m depth, a catenary cable connected at the corner buoy is the most reliable and feasible option. At 35 m, the lazy-wave configuration becomes more attractive due to improved curvature and tension margins, though with higher installation complexity.

Overall, reliable DPC design for offshore FPV requires an integrated approach that couples lay-out configuration, connection strategy, installation, and operations from the outset. This initial analysis indicates that a catenary DPC configuration is feasible for lightweight FPV systems in the North Sea, but an increase in cable bending stiffness is preferred to improve curvature control and design margins.