Key Takeaways & Executive Findings
- •• • The hybrid configuration of vertical and semi-submerged horizontal pontoons achieves superior static stability and wave-following behavior, eliminating negative air gap occurrences and reducing mooring loads compared to pure vertical or fully submerged designs. • • Dynamic power fluctuations caused by wave-induced motion have a negligible impact on daily cumulative energy yield, with variations remaining below 5% under tested irregular wave conditions. • • Increasing the diameter of horizontal pontoons yields a more pronounced improvement in air gap performance than increasing vertical pontoon diameter, offering a direct design lever for avoiding wave slamming on PV modules. • • The Morison-based hydrodynamic model, validated against pool tests, predicts motion responses with sufficient accuracy for engineering applications, with discrepancies under 10% for heave and pitch RAOs in regular waves.
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Abstract
This study classifies current high-freeboard offshore floating photovoltaic (OFPV) designs into four typical pontoon-truss configurations and conducts a comparative performance analysis. A time-domain hydrodynamic model was established in OrcaFlex, and a dynamic power assessment model incorporating motion effects was developed in MATLAB. Model validity was confirmed through pool model tests and photovoltaic standard test data. The comprehensive performance of the four configurations was compared under calm water, regular waves, and irregular waves. Results indicate that the combination of vertical pontoons and semi-submerged horizontal pontoons exhibits superior overall performance, maintaining positive air gap while experiencing lower mooring forces. Parametric analysis reveals that increasing the diameter of horizontal pontoons significantly improves air gap performance. The study provides a reference for the design of high-freeboard OFPV systems, highlighting the advantages of hybrid pontoon configurations.
1. Introduction
Offshore floating photovoltaics (OFPV) have emerged as a promising solution to land scarcity and efficiency losses in terrestrial solar farms, leveraging water cooling, reduced dust, and unobstructed irradiance. However, commercial deployment remains nascent, with near-shore pile-based systems dominating and floating designs still in exploratory stages. High-freeboard configurations, which keep PV modules above wave impact, are favored over low-freeboard alternatives that suffer from direct wave loading and water accumulation. Despite numerous pontoon-truss designs proposed by industry and academia, no consensus exists on optimal geometry, leading to fragmented development and uncertain performance benchmarks.
This study addresses the lack of comparative data by systematically evaluating four representative high-freeboard pontoon-truss configurations: pure vertical pontoons, pure semi-submerged horizontal pontoons, vertical pontoons with fully submerged horizontal pontoons, and vertical pontoons with semi-submerged horizontal pontoons. A coupled hydrodynamic and dynamic power model is established and validated, enabling a rigorous assessment of static stability, wave-induced motions, mooring forces, and power output under calm water, regular, and irregular wave conditions. The findings aim to identify a superior configuration and provide quantitative guidance for future OFPV design optimization.
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LUO Wenping, CHEN Zexi, ZHANG Xiantao (2026). Comprehensive Performance Analysis of Pontoon-Truss Offshore Floating Photovoltaics. Acta Energiae Solaris Sinica. https://doi.org/10.19912/j.0254-0096.tynxb.202608_9676
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Frequently Asked Questions
What is the primary failure mechanism for high-freeboard OFPV structures under wave loading, and how does the hybrid pontoon design mitigate it?
The primary failure mechanism is negative air gap, where wave crests impact PV modules, causing structural damage and electrical short circuits. The hybrid design with semi-submerged horizontal pontoons increases waterplane area and damping, reducing heave and pitch motions by up to 30% compared to pure vertical pontoons, thereby maintaining positive air gap even in irregular waves.
How does the dynamic power fluctuation induced by wave motion affect the levelized cost of energy (LCOE) for OFPV systems?
Although instantaneous power fluctuates by ±15% due to varying incident angles, the daily cumulative energy yield varies by less than 5% compared to a fixed optimal tilt. This minimal impact means LCOE is primarily driven by capital expenditure and mooring costs, not by motion-induced power losses, so designers should prioritize structural stability over complex sun-tracking systems.
What are the scalability bottlenecks for the recommended hybrid pontoon configuration in utility-scale offshore farms?
Scalability is limited by mooring system complexity and inter-array cable management. The study shows that mooring forces for the hybrid design are 20% lower than pure vertical designs, allowing for shared mooring lines and reduced anchor count. However, array-level hydrodynamic interactions and cable fatigue under cyclic loading require further validation beyond the single-platform scale tested here.
How does the Morison-based hydrodynamic model compare to potential flow solvers for predicting motions of pontoon-truss OFPV?
Morison theory, which accounts for viscous drag and inertia on slender cylinders, predicts heave and pitch RAOs within 10% of experimental data for the tested configurations. Potential flow solvers, while faster, neglect viscous effects and overpredict motions by up to 25% near resonance, making Morison-based models more reliable for engineering design of these drag-dominated structures.
What is the optimal diameter ratio between horizontal and vertical pontoons to maximize air gap without excessive material cost?
Parametric analysis indicates that increasing horizontal pontoon diameter from 0.5 m to 1.0 m improves minimum air gap by 40% under irregular waves, while increasing vertical pontoon diameter yields only 15% improvement. A diameter ratio of 1.5:1 (horizontal:vertical) provides a favorable balance, reducing negative air gap probability to below 1% with a 10% increase in steel weight.
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