Floating PV Systems Mainly Consists of Four Major Systems
Offshore Photovoltaics and Offshore Wind Power: A Complementary Relationship
Offshore photovoltaics and offshore wind power are not in competition. Drawing from the experience of inland wind and solar farms, offshore photovoltaics can be arranged around wind power towers, sharing submarine cables, combiner boxes, transformers, booster stations, and energy storage facilities with offshore wind power. This integration can significantly reduce the investment and maintenance costs of offshore renewable energy projects, thereby improving the return on investment.
The primary difference between floating photovoltaic systems and ground-based photovoltaic power stations lies in the replacement of ground piles and brackets with floating bodies, mooring systems, and anchoring components. Apart from higher specifications for component requirements, the design of other elements remains similar to that of onshore centralized power plants.
Floating Offshore Photovoltaic Power Plants
Floating offshore photovoltaic power plants replace traditional ground piles and brackets with floating bodies, mooring systems, and anchoring components. The floating offshore photovoltaic system primarily consists of four subsystems: the floating PV system, anchoring system, cable laying system, and grounding system.
Floating PV Systems
The floating system includes two parts: the photovoltaic array floating system and the electrical equipment floating system. Both are designed to meet the 25-year service life requirement of the floating PV system.
Floating materials provide buoyancy for photovoltaic power generation equipment and a working surface for construction and operational activities. Their quality is critical to the system's longevity. To withstand years of exposure to sea winds, waves, and marine microorganisms, the materials must meet high-quality standards. Early industry experiments used materials such as bamboo, concrete, stainless steel, fiberglass-reinforced plastic, aluminum-magnesium alloy, and high-density polyethylene (HDPE), with mixed results. After years of development, the industry now predominantly uses modified high-density polyethylene (modified HDPE) as the floating material.
Ordinary HDPE degrades under ultraviolet and high-energy radiation, leading to discoloration, surface cracking, brittleness, and loss of strength, making it unsuitable for a 25-year service life in marine environments. Additionally, during production processes like blow molding and injection molding, issues such as the "shark skin" phenomenon or melt fracture can occur. To meet the requirements of floating offshore photovoltaic power plants, ordinary HDPE must be modified for enhanced weather resistance and toughness. Key properties such as tensile strength, elongation, and impact strength must maintain at least 70% of their original values over a 25-year lifecycle.
Anchoring System
The anchoring system ensures the photovoltaic floating array remains within a specific range, preventing dispersion by sea winds or currents. It is critical for the reliable operation of the floating, laying, and grounding systems. The anchoring system comprises three parts: the counterweight anchoring system, specialized anchor system, and pile anchoring system. These components represent the main challenges in designing a "floating power station on water."
After assembling the photovoltaic array, it is towed to a suitable location for preliminary positioning and connected to the anchoring system. The array generates significant horizontal forces due to wind loads, water currents, and waves. While counterweight and specialized anchoring devices provide limited anchoring force, requiring numerous anchoring points, pile anchoring offers stronger anchoring force with fewer points. Pile anchoring is also suitable for subsidence areas but cannot be used in areas with waterproof layers.
Cable Laying System
The laying system varies depending on the type of cables being installed. It involves the installation of conduits or cables from one location to another and can be divided into AC/DC cable laying and collector line laying.
In floating PV systems, AC and DC cables are laid to facilitate construction and maintenance. Cables in the photovoltaic array area are fixed using floating boxes and cable trays. If collector lines are used, measures must be taken to accommodate water level fluctuations. High-voltage AC cables are first laid on the floating surface, followed by underwater installation. The design must ensure ease of maintenance, with cable lengths adjusted for water level changes. Additionally, the cable sheath material should be selected based on the natural conditions of the water area.
Grounding System
The grounding system consists of a mesh structure of grounding bodies formed by multiple metal electrodes and conductors buried underground. It is divided into the photovoltaic array grounding system and the electrical equipment grounding system. The total grounding grid's resistance must not exceed 4 ohms.
Grounding is crucial for floating power stations on water. The design must account for varying water surface conditions and component selection factors. Grounding downlines should include measures to adapt to water level changes and provide redundancy. A suitable grounding device must be selected to ensure system reliability.
