New model for offshore floating PV system design

By using a multi-physics framework that integrated mechanical and optoelectric properties of offshore floating PV systems, researchers at TU Delft in the Netherlands investigated structural loads experienced by a variety of floating PV structures and the related electrical power losses.

“Simulations like the ones we performed shine a light on which configurations will perform best before implementing them in a pilot system,” corresponding author Alba Alcañiz Moya told pv magazine, pointing out that the model enabled things like fatigue testing, extreme loading and life cycle analysis of the platform, “all of which are not easily doable on a physical test platform.”

“Finally, developing such a framework enables us to develop a digital twin of the platform,” she said.

Several floater configurations were examined, including single large floaters and multiple small floaters connected with free hinges. Structural design decisions were input, as well as wave movements and weather conditions such as high winds, irradiance, and optoelectronic performance to calculate yield. The optoelectrical formulation was numerically implemented in Python using the PVLIB-Python modeling tool produced by Sandia National Laboratory.

The results revealed a design trade-off for the number of floaters. Fewer floaters appeared to induce less PV motion and achieve better yield, whereas more floaters tended to enable less elastic stress to achieve a more durable structure.

“More floaters increase the stability of the system since the tension is distributed among them and the hinges allow more flexibility of movement. However, this flexibility of movement makes the modules move more, increasing the power mismatch losses,” explained Alcañiz Moya. “This trade-off provides us with an opportunity to identify the optimal balance for each location. Additionally, our study equips us with the tools and insights needed to pinpoint this ideal setup.” The team noted the influence of structural properties on the power mismatch losses in a variety of scenarios. “It is observed that the Young’s modulus of the material only has an impact for longer floaters where the elastic response dominates,” it said. “Conversely, changes in the cross-section fill ratio affect shorter floaters, where the rigid-body response prevails. The floater-beam thickness has the most significant impact across various floater lengths.”

In concluding remarks, the group stressed a “symbiosis” between offshore solar and offshore wind. “Opting for a large number of small floaters leads to a transition from elastic to rigid body response, resulting in minimal elastic stresses. Fortunately, the highest mismatch losses occur on sunny windy winter days, therefore periods of low generation. This lower generation can be compensated for by wind turbines, promoting the symbiosis between the two offshore renewable energy sources,” it said.

The details of the study were reported in “Structural Analysis and Power Losses in Floating Solar Platform in Offshore Environment,” published in Applied Energy.

Looking ahead, the researchers said that the focus will be on 3D analysis, investigating irregularly shaped floating PV platforms and interaction with mooring lines. “Further, the hydro-elastic model will be developed to account for the non-linearity in the ocean waves and the structural response. The exploration of alternative locations and different floating structures, such as membranes, is also worthwhile,” they noted.