# A Novel Accelerated Corrosion Test for Supporting Devices in a Floating Photovoltaic System
## 1 Introduction  
Over recent years, the market of photovoltaic systems has been expanding rapidly. In addition to common types of rooftop, ground-mounted, and building-integrated photovoltaic systems, countries from around the world have been actively developing a floating photovoltaic (FPV) system, which is mainly installed on surface of idle waters [1, 2]. The FPV system is highly suitable for countries that are densely populated and are highly dependent on imported energy, and it is expected to solve the development dilemma of insufficient land resources [3, 4]. Single-pile fixed systems or dual-pile fixed systems are suitable for shallow water or small water level changes, while floating systems with support or floating systems without support are suitable for deep water or large water level changes, as depicted in Figure 1. The common materials of supporting devices are hot-dipped galvanized steel or aluminum. Concrete piles are generally used in fixed systems and are piled into the ground directly under water. The materials used in floating systems are mainly engineering plastics, most of which are high density polyethylene (HDPE) [5]. Taiwan is surrounded by seas. A high temperature and humid environment coupled with air pollutants make metal supports, retainers, and screws corrode easily in the atmosphere, as shown in Figure 2a. Because of strong northeast monsoons, some solar panels are loosened and even fall off, as shown in Figure 2b. The corrosivity of the atmosphere is graded by six levels in ascending order, including C1 (very low), C2 (low), C3 (medium), C4 (high), C5 (very high), and CX (extreme) [6]. Based on the grading diagram for the corrosion rate in the Taiwan area in 2016, the atmosphere corrosivity of Taiwan was generally higher than level C3, and in some coastal areas the corrosivity level was greater than level C5, reaching level C5+ (that is level CX) [7]. The best way to evaluate the durability of metal supporting devices is to place them in a known corrosivity area and to apply the field exposure test directly. The corrosion tests of various structural materials (aluminum or coated steels) used in PV structures are conducted by exposing them to the sea, and the durability of materials is periodically evaluated according to the extent of corrosion [8]. Four anti-corrosion approaches can be applied in a marine environment [9], and four different polymeric coatings on 314 SS are introduced to prevent corrosion for marine applications [10]. Nevertheless, this test method takes an enormous amount of time. To evaluate the durability of supporting devices quickly and efficiently, it is practical to artificially produce a highly corrosive environment in order to conduct salt spray tests in the lab. Numerous studies have employed salt spray tests, not only on grounding connections [11], but also on glass [12] and modules [13] in PV systems. The results demonstrate that the presence of ions (Na\({}^{+}\), Cl\({}^{-}\), etc.) in salt water have a much greater effect on the corrosion rate of metal connectors than in just heat and high humidity [11]. As the test conditions of an artificial environment are usually harsher than that of an atmosphere environment, the test time can be reduced dramatically [14; 15]. The visual observation method, area observation method, and weight observation method are recommended to determine the degree of corrosion [16]. Figure 1: Types of floating photovoltaic (FPV) systems. Because environmental conditions on the surface of water are harsher than on the ground; however, regulations or standards relevant to the application of supporting devices in FPV system are insufficient now [17]. Currently, it is being planned that FPV systems in Taiwan will be installed on water areas, such as reservoirs, lakes, ponds, and fish farms, and there are a lack of data about whether the supporting devices will be safe enough to endure long term use [18].