# A Novel Accelerated Corrosion Test for Supporting Devices in a Floating Photovoltaic System
## 2 Materials and Methods  
The salt spray test is an accelerated test for corrosion resistance that is not only applicable to metals and their alloys, but also to the surface coverage layer or surface modification layer, for example anodic oxide film, chemical conversion film, electrodeposit, chemical deposit, organic coating layer, and so on. The salt spray test can be categorized into three methods according to corrosivity--neutral salt spray (NSS), acetic acid salt spray (AASS), and copper-accelerated acetic acid (CASS).  
In accordance with ISO 9227 [14], the NSS test consists of a neutral (pH = 6.5-7.2) 5 \(\pm\) 0.5% sodium chloride (NaCl) solution delivered to a nozzle by saturated compressed air. The free falling rate of spray should be controlled within 1.5 \(\pm\) 0.5 mL/h at 35 \(\pm\) 2 \({}^{\circ}\)C. The AASS test consists of an acidic (pH = 3.1-3.3) 5 \(\pm\) 0.5% NaCl solution that is tuned by an acetic acid solution, and thus the corrosion rate of AASS is faster than for NSS. The CASS test contains additional 0.0205 \(\pm\) 0.0015% cuprous chloride (CuCl\({}_{2}\)) added into the acidic (pH = 3.1-3.3) NaCl solution. Because copper ions promoted corrosion reactions to happen faster, temperatures were raised to 50 \(\pm\) 2 \({}^{\circ}\)C, so and CASS had a faster corrosion rate than AASS. The test time was determined by the material property and test demands, and included 2, 6, 24, 48, 96, 168, 240, 480, 720, and 1008 h, or any other specific time and interruption of test time as long as it did not exceed beyond one hour each day. The differences of three salt spray test conditions are listed in Table 1.  
Considering the stronger corrosivity of CASS, in this study, we preferentially utilized the CASS test because of its faster corrosion rate in order to simulate the long-term influence of corrosion for an atmospheric environment on the supporting devices on a water surface. We attempted employing a faster and more effective method to evaluate the durability of the supporting devices in the FPV system, and compared the varying corrosion extent of the supporting devices between NSS, AASS, and CASS. Generally speaking, the extent of corrosion in the one-day NSS test was equivalent to exposure to a coastal environment (level C5+) for 120 days or to a general environment (level C3) for one year. Similarly, the extent of corrosion in the one-day ASS test was equivalent to exposure to a coastal environment (level C5+) for 360 days or to a general environment (level C3) for three years.  
Figure 2: (**a**) Corrosion of metal supports, retainers, and screws, and (**b**) metal corrosion and strong wind loosen solar panels.  
The extent of corrosion in the one-day CASS test was equivalent to exposure to a coastal environment (C5+ level) for 960 days or to a general environment (C3 level) for eight years. It should be noted that aforementioned conversion formulas are merely empirical formulas, and the corrosion rate would be affected by the intrinsic property of metal material, the method of surface treatment, and the different deposit layers or coating layers.  
The CASS test conditions in this study are listed as follows:  
1. Concentration of salt solution: 5 \(\pm\) 0.5% NaCl + 0.0205 \(\pm\) 0.0015% CuCl\({}_{2}\)
2. pH of salt solution: 3.1-3.3
3. Temperature of salt solution and spray chamber: 50 \(\pm\) 2 \({}^{\circ}\)C
4. Pressure of saturated compressed air: 98 \(\pm\) 10 kPa
5. Average fog collection rate for a horizontal collecting area of 80 cm\({}^{2}\): 1.5 \(\pm\) 0.5 mL/h.
6. Test time: depending on the extent of corrosion.  
The test system for the salt spray corrosion used in this study is shown in Figure 3.