| Work Detail |
New Chinese research shows that using rigid connectors instead of polyester ropes in floating PV installations can help reduce the relative motion of floats and simplify the design of the connection system.
Researchers at Harbin Engineering University (China) have studied the use of rigid single-rod connectors in floating photovoltaic configurations and found that these connectors offer a number of advantages over polyester ropes.
The research group performed several numerical simulations with different sizes of floating PV systems, different rod lengths, and different degrees of freedom of movement. “Currently, many floats are connected by polyester ropes,” he explained. “However, as the PV deployment area increases, the number of polyester ropes and the complexity of their arrangement also increase, which poses potential problems. Compared with polyester cables, structural steel connectors offer advantages such as simplification of their arrangement. Therefore, applying structural steel connectors to connect PV floats is a promising approach.”
In their simulation, the scientists assumed that the floating system would be deployed in waters with a depth of 12.68 m. Each PV platform is supported by four small octagonal floats, made of high-density polyethylene (HDPE) and with an outer diameter of 2.8 m and an inner diameter of 1.2 m. A six-line mooring system is also used.
The floats are connected with 1.2 m rigid connectors, namely purely rigid connectors, articulated connectors and gimbal connectors. While purely rigid connectors do not release any degrees of freedom, articulated connectors allow relative rotation. Gimbal connectors allow rotation about two axes, reducing vertical and lateral bending moments, but are prone to self-locking effects under wave action. Each connector type was tested in configurations of two, four or eight PV panels. The case of a two-panel system was further investigated, with additional connector lengths of 0.5 m and 1.9 m.
“It has been demonstrated through validation that the three-dimensional potential flow theory can be well applied to the motion of floating PV systems,” the academics say. “In the rigid connectors between the floats, different joints are simulated by imposing constraints. The connection used in the paper is a single-rod connector. Therefore, constraints are imposed on both sides. In the numerical simulation, the connector joints are simplified into constraints, and different shapes of connectors are simulated by releasing degrees of freedom in different directions.”
Simulation results showed that purely rigid connectors experience significant longitudinal bending moments and vertical loads. In contrast, the release of degrees of freedom leads to a corresponding reduction in bending moments and loads. Cardan connectors experience longitudinal moments 4.86 times lower than purely rigid connectors under specific conditions.
“Importantly, in gimbal connectors, the self-locking effect reintroduces stiffness, generating additional bending moments,” the researchers noted. “This suggests that connectors lacking released degrees of freedom are unsuitable for the harsh offshore environments. To avoid self-locking, gimbal connectors should be used individually in areas with lower wind and wave conditions.”
To conclude their paper, the scientists explained that as the number of floats increases, the loads on the connectors progressively increase, and so does the likelihood of green water on deck. “The peak loads on the connectors in the eight-float and four-float configurations are significantly higher than those in the two-float configuration, and the point of maximum load shifts towards the centre as the float configuration is enlarged,” they stated. “This finding indicates that the central section of the multi-float system is particularly vulnerable.”
The results were presented in “ Hydrodynamic analysis of floating photovoltaic system constrained with rigid connectors,” published in Scientific Reports . Scientists from Chinese offshore specialist Yantai CIMC Raffles participated in the research team. |
