**1. Introduction**

With a new climate system that replaces the Kyoto Protocol, which expired in 2020, the Paris Climate Agreement has been applied since January 2021, which includes strengthening global warming control targets and reducing greenhouse gas emissions. As follow, various policies have been enacted to encourage the development of new renewable energy sources to reduce greenhouse gas emissions.

In addition to international treaties, South Korea is promoting a "Renewable Energy 3020" policy to increase the ratio of renewable-energy power generation by 2030. The goal of the policy is to increase the renewable energy power generation ratio by 20% or more, and to supply over 95% of the capacity of the newly installed platform with clean energy such as solar and wind power [1]. Since 2012, the Renewable Portfolio Standard (RPS), which mandates a certain percentage of power generation as new renewable energy for industrialization such as solar power, wind power, and hydrogen, has also been enforced [2].

Recently, in the case of solar power generation, the demand for installation on water (e.g., lakes, coasts, and on the sea) is increasing rapidly due to the lack of installation area on land. It is more convenient to secure space on water and in the sea than on land, minimizes the effect of natural disasters, and eases the development large-scale power generation complexes [3].A floating solar power farm system is frequently used as a unified platform considering its installation convenience, expandability, and mobility.

On the other hand, since the coast and sea are exposed directly to natural disturbance (e.g., seawater, wind, and waves), technologies that can minimize the effects of waves and actively reduce fluctuations are needed [4–6]. Owing to the periodic motion of waves, fatigue loads are generated on structures (e.g., floating bodies, supporting frames, panels,

**Citation:** Lee, J.-H.; Paik, K.-J.; Lee, S.-H.; Hwangbo, J.; Ha, T.-H. Experimental and Numerical Study on the Characteristics of Motion and Load for a Floating Solar Power Farm under Regular Waves. *J. Mar. Sci. Eng.* **2022**, *10*, 565. https://doi.org/ 10.3390/jmse10050565

Academic Editor: Eugen Rusu

Received: 31 March 2022 Accepted: 19 April 2022 Published: 21 April 2022

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and coupling devices), and a design is needed for supporting structures considering structural stability. To consider the stability of a floating solar power generation system, experiments and numerical studies on the motion performance and connections between adjacent platforms are still underway.

Oliveira-Pinto et al. [7] provided a literature review on the applicability of floating solar power farms and introduced the technologies currently available, as well as the technical challenges and risk factors when designing studies in the marine environment.

Sahu et al. [8] illustrated the concept and advantages of floating solar power systems and studied each component of solar power systems. The environmental loads can cause deformation and stress in the module, causing microcracks and reducing productivity and durability. The technology of thin-film research was proposed to withstand harsh environmental conditions. It was noted that remote sensing and GIS (geographic information system)-based technologies can be utilized to determine the potential of solar panels.

The floating structure uses individual HDPE (high-density polyethylene), and the floating bodies were connected to a pin. It was said that the connection part was weak due to environmental factors. When this connector is exposed to high wave heights, stress concentration could occur and cause system problems. It was shown that the behavior of floating systems is complex [9,10].

Shi et al. [11] introduced a network modeling method for the dynamic prediction of multimodule floating structures and conducted it experimentally in the wave. The connector was made on three-axis motion, and RAOs (response amplitude operator) were compared at various frequencies through the experiment. Recently, the SCOTRA company developed a connector system that allows floating bodies to have their own motility in all directions.

When waves interact with a floating solar power farm (FSP), the motions of the FSP generate inertial forces and dynamic loads on the structures. Non-linear effects make it difficult to predict what will happen on the platforms. It could increase the motion response complexity exponentially of floating bodies. Therefore, recent studies are trying to predict the motion of the system using the using the computational fluid dynamics (CFD) [12,13].

All previous studies have stated that it is important to predict the load at the design stage due to the non-linear environmental factors that affect the FSP depending on the wave conditions. Also, it is necessary to consider motion response with different FSP components (e.g., connecting method, the type of mooring system, the array of floating bodies, and the position and angle of the solar panel).

In this study, we focused on the motion response and tried to understand the relative motion that may occur in a unit platform. Owing to the establishment of numerical techniques, the simulations were performed for a floating solar power farm in the form of a unit under wave conditions. Uniaxial hinge and catenary techniques were applied to the connector and mooring system to determine the motion performance of the floating solar power farm for six degrees of freedom (6DOF). This was verified by an experiment conducted in the Inha University towing tank (IUTT). It investigated fluid forces such as load and pressure distribution, which are difficult to determine using the experiment.
