# Wind Loads on a PV Array
## 2 Experimental Setup  
The experiments were performed in a closed-loop wind tunnel at the Architecture and Building Research Institute (Tainan, Taiwan). The wind tunnel has a working cross section of 2.6 m (height) \(\times\) 4 m (width) \(\times\) 36.5 m (length) and a contraction ratio of 4.71. To determine the critical wind loads, a 1/10 scale stand-alone array (nine inclined panels, P1-P9; \(L\) = 168 mm and \(W\) = 900 mm) was constructed, as shown in Figure 1. The origin of the coordinates (\(\chi\)/\(L\) = 0 and \(y\)/\(W\) = 0) is located at the upper left corner of the inclined plate. When the low surface faces the flow, this corresponds to \(\beta\) of 0\({}^{\circ}\). The lift coefficient, \(C_{L}\), is negative in the upward direction. The model sits 10 mm above the tunnel floor and the blockage ratio is up to 1.4%.  
Meteorological data from nearshore buoys in Taiwan (Qigu, Longdong and Hsinchu) were collected [19] to determine the test conditions. The most common values of \(\beta\) for Qigu (23\({}^{\circ}\)05\({}^{\prime\prime}\)42\({}^{\prime\prime}\) N) were 210\({}^{\circ}\)-225\({}^{\circ}\) and 315\({}^{\circ}\)-360\({}^{\circ}\) for the period of 2013-2017. In Longtong (25\({}^{\circ}\)05\({}^{\prime\prime}\)48\({}^{\prime\prime}\) N) and Hsinchu (24\({}^{\circ}\)45\({}^{\prime\prime}\)19\({}^{\prime\prime}\) N), the respective values for \(\beta\) were 0\({}^{\circ}\) and 30\({}^{\circ}\)-45\({}^{\circ}\). The variation in \(\alpha\) for PV panels with respect to wind was \(\pm\)45\({}^{\circ}\). In this study, the value of \(\alpha\) was between 10\({}^{\circ}\) and 80\({}^{\circ}\) (in increments of 10\({}^{\circ}\)) and the value of \(\beta\) ranged from 0\({}^{\circ}\) to 180\({}^{\circ}\) (in increments of 15\({}^{\circ}\)). Note that the angle between the PV arrays and the surface of the sea is fixed for an offshore-type PV system. This is not the case for the wind tunnel tests. However, the experimental results of this study can be used for preliminary structural designs of an offshore PV array and to validate the numerical simulation.  
For an inclined panel for which \(L\)/\(W\) = 2, [PERSON] et al. [12] showed that there is a small increase in wind load when there is an increase in the intensity of the freestream turbulence. Therefore, the experiments for this study used a uniform flow. The freestream velocity was 14.5 \(\pm\) 0.1 m/s, and the turbulence intensity was 0.3%. A Pitot-static tube was positioned at the same height as the front edge of the inclined panels to determine the static, \(p_{\infty}\), and the dynamic pressure, \(q\), for the incoming flow. The Reynolds number, which is based on the length of the inclined panels, was 1.64 \(\times\) 10\({}^{5}\). Note that there is Reynolds number independence for an inclined panel [20]. A total of 434 pressure taps were drilled on the upper and lower surfaces of the model. Flexible polyvinyl chloride tubes of 1.1 mm in diameter and 60 cm in length were connected to SCANIVALVE multichannel modules (Model ZOC 33/64 Px 64-port; Model RAD3200 pressure transducer, Scanivalve Co., Liberty Lake, WA, USA) to measure the mean surface pressure. The full-scale range of the sensors was \(\pm\)2490 Pa, and the accuracy was \(\pm\)0.15% of the full scale. The sampling rate was 250 Hz, and each record had 32,768 data points. The mean pressure coefficient, \(C_{p}\) (= (\(p-p_{\infty}\))/\(q\)), and \(C_{L}\) (= \(\frac{1}{A}\int_{A}\Delta C_{p}\)cos (\(\alpha\))\(dA\)) were calculated. The differential pressure coefficient, \(\Delta C_{p}\) (= \(C_{p,up}-C_{p,low}\)) was determined using the value of \(C_{p}\) for the upper and lower surfaces.  
Figure 1: Test configuration for a stand-alone array.