# Floating Photovoltaic Plant Monitoring: A Review of Requirements and Feasible Technologies
## 2 PV Floating Plants  
PV modules are generally installed over the ground and rooftops using rigid mounting structures, whose technical and economic issues are well assessed in the literature [13]. However, due to limited land availability, dense populations, and significant deforestation threats, there is increasing interest in installing photovoltaic modules over water bodies such as canals, lakes, reservoirs, and oceans. These installations are generally referred to as water-based photovoltaics (WPVs), which include floating freshwater PV, offshore PV, underwater PV, and canal-top PV systems [14]. Specifically, according to [15], floating photovoltaic systems can be divided into four types: pile-based, floating, tracking systems, and water level variation systems. The first three types are mainly used in shallow water bodies with stable water levels and calm surfaces, such as lakes (including saltwater lakes), rivers, and fishponds. The last category, water level variation systems, is designed for use in reservoirs with significant water level fluctuations, such as pumped storage reservoirs. It is also possible to integrate tracking systems into both floating and pile-based PV systems [16; 17]. It is worth noting that evaporation reduction, in this case, directly translates into energy efficiency savings, for obvious reasons. Recently, there has also been increasing interest in offshore FPV solutions, with the first offshore FPV system established in the Netherlands in 2017, a decade after the first FPV system in Japan [18; 19]. Despite the challenging operating conditions of marine FPV systems, such as high waves, high winds, and a corrosive atmosphere, industrial and research institutions are actively working to develop and enhance various FPV solutions for marine environments. These marine FPV systems differ significantly from freshwater FPV systems and aim to achieve adequate operational safety and cost-efficiency [20]. A schematic view of an FPV system is shown in Figure 1, its key components being a floating platform, mooring and anchoring systems, PV modules, electric cables, and connectors [21]. Notably, a lightning protection system is also present. The threat of lightning to floating photovoltaic power plants arises from several factors. Firstly, their location in open areas, such as the surface of a water reservoir, poses a significant risk. Additionally, the sharp upper edges of the photovoltaic modules, which are mounted at an angle on supporting structures, concentrate the electric field. This concentration can increase the likelihood of a lightning strike hitting one of the modules [22]. The floating platform is the most crucial component of floating photovoltaic systems. It supports all components of PV generators and as well as the supporting structure (when used), and furthermore provides the right buoyancy, including a space for human accessibility, also considering operating conditions (high wind, waves, and when applicable, snow weight). Hence, the choice of the design and related material is fundamental. Floating platforms are mostly made of high-density polyethylene (HDPE), which is UV-resistant, corrosion-resistant, and has a high tensile strength, but there are other materials available, such as medium-density polyethylene (MDPE), fiber-reinforced plastic (FRP), and ferrocement [23; 24]. From the design point of view, floating platforms can be categorized, as reported in [25] as pure float, which is made of shaped floats that can hold PV modules directly, and pontoon plus a metal structure, which uses a metal structure to connect the elements that provide buoyancy by means of metallic elements (the PV modules are held by a metallic structure similar to PV land-based system). As stated in [20], using flexible crystalline silicon-based modules backed with foam may be less expensive than pontoon-based FPV systems. Ocean Sun technology lays rigid crystalline silicon modules on a reinforced flexible membrane.